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Chapter 12

Spinal, Epidural, and Caudal Anesthesia:Anatomy, Physiology, and Technique

Cynthia A. Wong, M.D.

Naveen Nathan, M.D.

David L. Brown, M.D.

ANATOMY 223

Obstetric Pain Pathways 223

Anatomic Changes of Pregnancy 223

Vertebral Anatomy 224

PHYSIOLOGY 227

Physiology of Neural Blockade 227

TECHNIQUE 227

Patient Position 227

Choice of Drug 229

Equipment and Needle and Catheter Placement 230

COMPLICATIONS OF NEURAXIALTECHNIQUES 238

Unintentional Dural Puncture 238

Unintentional Intravascular or SubarachnoidInjection 239

Inadequate Anesthesia 240

Equipment Problems 241

Resuscitation of the Obstetric Patient 242

Regional anesthesia is used extensively for obstetricpatients. Of the estimated 4 million women that givebirth in the United States each year, approximately 60%receive regional anesthesia. Of these, the overwhelmingmajority receive spinal or epidural analgesia or anesthesia.The purpose of this chapter is to review the anatomy, phy-siology, and techniques relevant to the administration ofneuraxial anesthesia in obstetric patients. Technical fea-tures represent only one element of the successful use ofspinal or epidural anesthesia. Conversely, sound medicaljudgment is of little benefit if a physician uses inadequatetechnique.

ANATOMY

Obstetric Pain Pathways

Pain during the first stage of labor results primarily fromchanges in the lower uterine segment and cervix. Pain istransmitted by visceral afferent nerve fibers that accompanythe sympathetic nerves and enter the spinal cord at the T10to L1 segments. During the late first stage and second stageof labor, pain results from distention of the pelvic floor,vagina, and perineum. Pelvic pain is transmitted by somaticnerve fibers, which enter the spinal cord at the S2 to S4segments (Figure 12-1).

During cesarean delivery, additional nociceptive path-ways are involved in the transmission of pain. Most cesar-ean deliveries are performed with a horizontal (e.g.,Pfannenstiel) skin incision, which involves the infraumbili-cal T11 to T12 dermatomes. During surgery, stretching ofthe skin may involve dermatomes two to four levels higher.Intraperitoneal manipulation and dissection involve poorlylocalized visceral pain pathways. Visceral pain may betransmitted by pathways as high as the celiac plexus.Additional somatic pain impulses may occur as a result ofdiaphragmatic stimulation, because the intercostal nervesinnervate a portion of the peripheral diaphragm.

Anatomic Changes of Pregnancy

The normal anatomic changes of pregnancy affect the useof neuraxial anesthesia techniques. Uterine enlargementand vena caval compression result in engorgement of theepidural veins. Unintentional intravascular cannulation andinjection of local anesthetic are more common in pregnantpatients than in nonpregnant patients. In addition, the ver-tebral foraminal veins, which are contiguous with the epi-dural veins, are enlarged and obstruct one of the pathwaysfor anesthetic egress from the epidural space during admin-istration of epidural anesthesia. The enlarged epidural veinsalso may displace cerebrospinal fluid (CSF) from the thora-columbar region of the subarachnoid space, as does the

Chapter 12 Spinal, Epidural, and Caudal Anesthesia: Anatomy, Physiology, and Technique 223

greater intra-abdominal pressure of pregnancy; this dis-placement partly explains the lowered dose requirementfor spinal anesthesia in pregnant women.2 Subarachnoiddose requirements are also affected by the lower specificgravity of CSF in pregnant patients than in nonpregnantpatients.3

The hormonal changes of pregnancy affect the periver-tebral ligamentous structures, including the ligamentumflavum. The ligamentum flavum may feel less dense and‘‘softer’’ in pregnant women than in nonpregnant patients;thus, feeling the passage of the epidural needle through theligamentum flavum may be more difficult. It may also bemore difficult for a pregnant woman to achieve flexion ofthe lumbar spine. Progressive accentuation of lumbarlordosis alters the relationship of surface anatomy to thevertebral column (Figure 12-2). At least three changes mayoccur. First, a pregnant woman’s pelvis rotates on the longaxis of the spinal column; thus, the line joining the iliaccrests assumes a more cephalad relationship to the verte-bral column (e.g., this imaginary line might cross the ver-tebral column at the L3 to L4 interspace rather than the L4to L5 interspace). Second, there is less space between adja-cent lumbar spinous processes during pregnancy. It may bemore difficult to use the midline approach to identify theepidural or subarachnoid space in pregnant women. (Thusthe often-heard comment, ‘‘She has a narrow interspace.’’)Third, magnetic resonance imaging has shown that theapex of the lumbar lordosis is shifted caudad during preg-nancy, and the typical thoracic kyphosis in women isreduced during pregnancy.4 These changes may influencethe spread of intrathecal anesthetic solutions in supinepatients (Figure 12-3). Finally, labor pain makes it moredifficult for some women to assume and maintain anideal position while the anesthesia provider performsneuraxial anesthesia.

Vertebral Anatomy

The administration of neuraxial anesthesia requires a com-plete understanding of the lumbar and sacral vertebral andperivertebral anatomy. Local anesthetics ultimately produceanesthesia through their effects on the spinal cord andnerve roots. The cephalad aspect of the spinal cord is con-tinuous with the brainstem through the foramen magnum.In women of childbearing age, the spinal cord terminates asthe conus medullaris at the level of the lower border of thefirst lumbar vertebral body. The conus medullaris isattached to the coccyx by means of a neural-fibrous bandcalled the filum terminale, which is surrounded by thenerves of the lower lumbar and sacral roots, known as the

L4

Intercrestline

FIGURE 12-2 The surface anatomy used toestimate the lumbar vertebral level. In pregnantwomen, the interiliac crest line (Tuffier’s line) maybe slightly higher in relation to the lumbarvertebral axis because of the difficulty in flexingthe lumbar spine.

T10

L1

S2

S3

S4

T12

T11

FIGURE 12-1 Pain pathways during labor and delivery. The afferentpain pathways from the cervix and uterus involve nerves thataccompany sympathetic fibers and enter the neuraxis at T10 to L1.The pain pathways for the pelvic floor and perineum include thepudendal nerve fibers, which enter the neuraxis at S2 to S4.

224 Part IV Foundations in Obstetric Anesthesia

cauda equina (Figure 12-4). Within the bony vertebralcolumn are three membranes: the pia mater, the arachnoidmater, and the dura mater. The pia mater is a highly vas-cular membrane that closely invests the spinal cord anddistally forms the filum terminale. The arachnoid mater isa delicate nonvascular membrane closely attached to thethird and outermost layer, the dura. The subarachnoidspace, located between the pia mater and arachnoidmater, contains (1) cerebrospinal fluid (CSF), (2) spinalnerves, (3) a trabecular network between the two mem-branes, (4) blood vessels that supply the spinal cord, and(5) lateral extensions of the pia mater—the dentate liga-ments (these ligaments supply lateral support from thespinal cord to the dura mater). Although the spinal cordends at the level of the bodies of L1 and L2 in mostpatients,5 the subarachnoid space continues to the S2level. At the end of the spinal cord, the cauda equinabegins and continues to the level of S2.

The outermost membrane in the spinal canal is a longi-tudinally organized fibroelastic membrane called the duramater. This layer is a direct extension of the cranial duramater and extends from the foramen magnum to S2, wherethe filum terminale blends with the periosteum of thecoccyx. A potential space (i.e., the subdural space) existsbetween the dura and the arachnoid mater. The duralborder cells have lower collagen content and few cell junc-tions, allowing for easy shearing after needle penetrationand fluid injection.6 This ‘‘space’’ is not used intentionallyby anesthesia providers. Unintentional subdural injectionmay explain some cases of failed spinal anesthesia; it mayalso explain the rare, slow-to-develop cases of high spinalanesthesia after the negative epidural test dose result andinjection of additional local anesthetic.

Immediately external to the dura mater is the epiduralspace, which extends from the foramen magnum to thesacral hiatus. The posterior longitudinal ligaments formthe anterior boundary of this space. The pedicles andintervertebral foramina form the lateral boundaries, andthe ligamentum flavum forms the posterior boundary.The contents of the epidural space include nerve roots,fat, areolar tissue, lymphatics, and blood vessels, includingthe well-organized venous plexus of Batson. The epiduralspace is segmented and discontinuous; it is not the uniformcylindrical space many writers have described. As shown inFigure 12-5, the shape and contents of the epidural spacevary with the level of cross section.7

Epiduroscopy and epidurography suggest the presence ofa dorsal median connective tissue band in some individuals.Anatomic dissection and computerized tomographic epidu-rography have also suggested the presence of epidural spacesepta. This band (or these septa) may provide an explana-tion for unilateral or incomplete epidural anesthesia.8

However, some investigators have suggested that thedorsal median band is an artifact of epidural space disten-tion or an anatomic manifestation of the previouslyunappreciated epidural space segmentation.9

T7L4-5

T8

L4

FIGURE 12-3 The curvature of the spinal column in the pregnantfemale (top) and nonpregnant female (bottom). The large and smallwhite arrows indicate the uterus and fetal head, respectively. Theapex of the lumbar lordosis moves caudad (triangular arrow), and thethoracic kyphosis is reduced and moves cephalad (triangular arrow) inthe pregnant woman. (Reprinted with permission from Hirabayashi Y,Shimizu R, Fukuha H. Anatomical configuration of the spinal columnin the supine position. II. Comparison of pregnant and non-pregnantwomen. Br J Anaesth 1995; 75:6-8.)

L4

L5

S1Internal filum

terminale

Ligamentumflavum

Duramater

Conusmedullaris

Caudaequina

Epiduralspace

Distaldural sac

S2

L2

L1

L3

FIGURE 12-4 Distal centroneuraxis anatomy. In pregnant women,the spinal cord ends at the lower border of the first lumbar vertebralbody. The subarachnoid space continues to the second sacralvertebral level.


The ligamentum flavum lies posterior to the epiduralspace. Historically some physicians have described the lig-amentum flavum as a single ligament. In actuality, however,it is composed of two curvilinear ligaments that join in themiddle and form an acute angle with a ventral opening(Figure 12-6).9,10 The ligamentum flavum is not uniformfrom skull to sacrum; indeed, it is not uniform evenwithin a single intervertebral space. The thickness of the

ligamentum flavum varies with vertebral level and posi-tion,11 as does the distance between the skin and the epi-dural space (Table 12-1).12,13 Hormonal changes may causethe ligamentum flavum to feel ‘‘softer’’ in pregnant womenthan in nonpregnant patients.

The lamina, the spinous processes of the vertebralbodies, and the interspinous ligaments lie posterior to theligamentum flavum. Posterior to these structures are thesupraspinous ligament (which extends from the externaloccipital protuberance to the coccyx), subcutaneoustissue, and skin (Figure 12-7).

Successful administration of caudal epidural anesthesia iscomplicated by widespread variations in sacral anatomy.Developmentally, the five sacral vertebrae fuse to formthe sacrum. The sacral hiatus results from the failure ofthe laminae of S5, and usually part of S4, to fuse in themidline. The sacral hiatus is covered posteriorly by the pos-terior sacrococcygeal ligament, which is the functionalcounterpart to the ligamentum flavum. The shape of thebony defect varies from a narrow, slit-like opening to awide-based, inverted ‘‘V.’’ The sacral hiatus is absent inapproximately 5% of all adult patients, and such an absenceprecludes the administration of caudal anesthesia.14 Thesacral hiatus is less likely to be absent in obstetric patients

Ligamentumflavum

Epiduralspace

A

B

FIGURE 12-5 A, Sagittal section of the epidural space demonstratesthat the contents of the epidural space depend on the level of thesection. B, Three-dimensional drawing of the epidural space shows thediscontinuity of the epidural contents. However, this potential spacecan be dilated by the injection of fluid into the epidural space.(Redrawn from the Mayo Foundation. From Stevens RA. Neuraxialblocks. In Brown DL, editor. Regional Anesthesia and Analgesia.Philadelphia, WB Saunders, 1976:323.)

Ligamentumflavum

Supraspinousligament

Interspinousligament

FIGURE 12-6 A horizontal section of the ligamentum flavum andassociated neuraxis structures is shown next to an oblique parasagittalsection of the lumbar vertebral neuraxis. The horizontal sectionillustrates the posterior ligamentous structures of the spinal column.The ligamentum flavum is composed of two leaves that meet in themidline at 90 degrees. The interspinous and supraspinous ligaments lieexternal to the posterior portion of the ligamentum flavum.

TABLE 12-1 Distance from the Skin to the Epidural Spacein 1000 Parturients

Distance (cm)

LumbarInterspace Median

5thPercentile

95thPercentile

L1-2 4.23 3.12 6.33L2-3 4.86 3.29 7.32L3-4 4.93 3.57 7.44L4-5 4.78 3.25 6.75

From Harrison GR, Clowes NWB. The depth of the lumbar epidural

space from the skin. Anaesthesia 1985; 40:685-7.

Ligamentum flavum

Subcutaneous fat

Skin

Dura mater and arachnoid

Interspinous ligament

Supraspinous ligament

FIGURE 12-7 Midline sagittal anatomy of the vertebral column. Whena needle is placed into the cerebrospinal fluid, it must pass throughskin, subcutaneous fat, the supraspinous ligament, the interspinousligament, the ligamentum flavum, the epidural space, and finallythe dura mater and arachnoid.


than in older patients, because ossification of this openingseems to increase with age.

The interior of the sacrum contains the sacral canal,which in turn contains the terminal portion of the duralsac. The dural sac terminates cephalad to a line joining theposterior superior iliac spines at the level of the secondsacral segment. The sacral canal also contains a venousplexus, which is part of the valveless internal vertebralvenous plexus.

PHYSIOLOGY

Safe, successful administration of neuraxial anesthesia inpregnant women requires an understanding of the normalphysiologic changes of pregnancy (see Chapter 2).Anesthesia providers, obstetricians, and nurses must appre-ciate the potential for aortocaval compression during spinaland epidural anesthesia. Only 10% of unanesthetized preg-nant women manifest clinical evidence of the supine hypo-tension syndrome.15,16 However, the sympathectomy andvasodilation that accompany neuraxial anesthesia causewomen to be more susceptible to the effects of aortocavalcompression. These undesirable hemodynamic changes canbe mitigated by avoidance of aortocaval compression, par-ticularly during the maintenance of spinal or epidural anal-gesia or anesthesia. Physicians and nurses should maintainleft uterine displacement during labor or when performinga vaginal examination or placing a fetal scalp electrocardio-gram (ECG) electrode or urethral catheter.

The greater oxygen consumption and diminished func-tional residual capacity associated with pregnancy result ina faster onset of hypoxemia during maternal apnea.Aortocaval compression hastens the onset of cardiovascularcollapse during high/total spinal anesthesia, and resuscita-tion is more difficult. Anesthesia providers should admin-ister spinal or epidural anesthesia only in a physical settingin which complications, such as unintentional intravenousor subarachnoid injection of local anesthetic, can be rapidlyand efficiently managed. In cases of cardiovascular collapse,endotracheal intubation may be necessary to facilitatemechanical ventilation and oxygenation and to protectthe lungs from aspiration of gastric contents. Equipmentand supplies necessary for laryngoscopy, intubation, andmechanical ventilation should be immediately available.

Physiology of Neural Blockade

Hormonal changes, anatomic changes, and decreases inCSF specific gravity likely are responsible for the lowerlocal anesthetic dose requirements during spinal anesthesiain pregnant women.3,17 Local anesthetics produce conduc-tion blockade primarily by blocking sodium channels innerve membranes, thereby preventing the propagation ofneural impulses. Differential blockade is manifested as dif-ferences in the extent of cephalad blockade of temperaturediscrimination and vasomotor tone, sensory loss to pin-prick, sensory loss to touch, and motor function.18

Temperature discrimination and vasomotor tone areblocked to the greatest extent (i.e., most cephalad level),and motor function to the least extent. During spinalanesthesia, local anesthetics act directly on neural tissuein the subarachnoid space. Regression of anesthesia can

be explained by the simple vascular uptake of localanesthetic from the subarachnoid space and spinal cord.19

Epidural anesthesia has a much smaller zone of differen-tial motor-sensory-sympathetic blockade; this differencesuggests that the mechanism of epidural anesthesia mustinvolve more than simple diffusion across the dura. Formany years, nerve fiber size was presumed to be the pri-mary determinant of susceptibility to local anesthetic block-ade (i.e., smaller fibers are blocked more readily than largerfibers). However, later studies have shown that the length ofnerve fiber exposed to local anesthetic is as important as thesize of the nerve fiber. Fink18 hypothesized that the lengthof nerve fiber exposed to local anesthetic affects the extentof the differential zone of motor and sensory blockade.With spinal anesthesia, the local anesthetic concentrationrequired to block sufficient sodium channels to affectmotor, sensory, and sympathetic function is less than thatneeded for the better-protected nerves found in the epidu-ral space; thus, a wider band of differential blockade occursduring spinal anesthesia than during epidural anesthesia.

The understanding of the mechanisms of spinal and epi-dural anesthesia likely remains oversimplified. Nonetheless,it seems clear that spinal anesthesia results primarily fromthe effects of local anesthetic on the spinal cord, whereasepidural anesthesia results from the effects of local anes-thetic on nerve tissue within both the epidural andsubarachnoid spaces.

TECHNIQUE

Contraindications for neuraxial techniques include the fol-lowing: (1) patient refusal or inability to cooperate; (2)increased intracranial pressure as a result of a masslesion, which may predispose the patient to brainstem her-niation after dural puncture; (3) skin or soft tissue infectionat the site of needle puncture; (4) frank coagulopathy; (5)uncorrected maternal hypovolemia; and (6) inadequatetraining or experience in the technique. Whether mild orisolated abnormalities in tests of blood coagulation precludethe use of regional anesthesia is controversial. However, it isclear that the prophylactic administration of low-molecu-lar-weight heparin is a clinical risk factor that mandatescaution in the administration of neuraxial anesthesia.20

The anesthesia provider should weigh the risks and benefitsof neuraxial anesthesia for each patient.

Patient Position

Pregnant women have an exaggerated lumbar lordosis, andit is more difficult for them to flex the lumbar spine.However, most pregnant women are young, and youth usu-ally allows sufficient flexibility to facilitate the insertion of aneedle into the epidural or subarachnoid space. Whetherthe block is initiated in the lateral or sitting position is amatter of provider and patient preference. Most obstetricpatients may assume the lateral decubitus position comfort-ably during the administration of spinal or epiduralanesthesia; this position likely has less adverse effect onvenous return and cardiac output than the sitting positionand may allow easier fetal monitoring. Vincent andChestnut21 performed a study in which they observedthat neither the sitting nor the lateral position was


consistently superior with regard to patient comfort.However, pregnant women who preferred the left lateraldecubitus position weighed less and had lower body massindices than women who preferred the sitting position.

An assistant should be present to help the patient andmonitor the fetus. If possible, the fetus should be monitoredduring, or at a minimum, immediately after all procedures.Equipment and drugs should be easily at hand and checkedin advance of the procedure. Meticulous sterile techniqueincludes thorough hand washing and the donning of ahat, mask, and sterile gloves by the anesthesia provider; theapplication of a skin disinfectant over a wide area of the lowerback; and the use of a sterile barrier or drape. The donningof a sterile gown by the anesthesia provider is controversial.

When spinal or epidural anesthesia is performed withthe patient in a lateral position, the patient’s back shouldlie at, and parallel to, the edge of the bed, for at least tworeasons. First, the edge is the most firm section of themattress. If the patient lies away from the edge of thebed, the patient’s weight will depress the mattress, andthe anesthesia provider must work in a ‘‘downhill’’ direc-tion. Second, this position allows anesthesia providers tokeep their elbows flexed, facilitating control of fine handand wrist muscle movements. The plane of the entireback should be perpendicular to the mattress. Whenasked to flex the lower back, patients typically roll thetop shoulder forward, an action that rotates the spine(which is undesirable) but does not flex the lower back.

Similarly, patients positioned sitting should have theirfeet supported by a stool with the backs of their kneesagainst the edge of the bed, a maneuver that helps positionthe patient’s back closer to the anesthesia provider. Theshoulders should be relaxed symmetrically over the hipsand buttocks. Beds in obstetric units often break at thefoot, and the split in the mattress encourages the patient’sseat to slope downhill if she is straddling the mattress split;this position will cause spine rotation and may make theprocedure more difficult.

The sitting position is likely associated with a higherincidence of orthostatic hypotension and syncope.However, the sitting position is preferred—and may berequired—in obese parturients, in whom identification ofthe midline is significantly easier with the sitting position.Further, morbidly obese women may experience hypoxemiawhen placed in the lateral decubitus position. One studydemonstrated a greater reduction in maternal cardiacoutput with maximal lumbar flexion in the lateral decubitusposition than in the sitting position during identification ofthe epidural space.22 The investigators in this study specu-lated that maximal lumbar flexion in the lateral decubitusposition results in concealed aortocaval compression.

When spinal anesthesia is performed, the patient’s pos-ture relative to anesthetic baricity should be considered, asit influences the extent of blockade, the latency of blockade,and the incidence of hypotension. The incidence, timing,and extent of hypotension in the period immediately afterinitiation of the block depend on the type of block(i.e., spinal, epidural, or combined spinal-epidural), drugcharacteristics (e.g., baricity, concentration), patient posi-tion during the procedure, and patient position in theperiod following the procedure. For example, when spinalanesthesia is initiated with a hyperbaric solution for instru-mental vaginal delivery, it often makes sense for the patient

to be sitting to ensure the rapid onset of sacral anesthesia.Conversely, spinal anesthesia for cervical cerclage can beinitiated in the steep lateral Trendelenburg position witha hypobaric anesthetic solution.

Posture has less influence on the spread of epidural anes-thesia.23-25 During epidural anesthesia, a unilateral blockmore likely results from the malposition of the catheter(or perhaps an anatomic barrier within the epidural space)than from patient position, particularly after a bolus injec-tion. Norris et al.25 observed that gravity did not augment thespread of anesthesia in patients receiving epidural anesthesiafor cesarean delivery, and they concluded that posture doesnot need to be manipulated to ensure adequate bilateralepidural anesthesia. At least two studies have noted thatthe use of the sitting position is not necessary for the devel-opment of good sacral anesthesia when large volumes ofepidural local anesthetic are given for cesarean delivery.24,25

However, Reid and Thorburn24 observed that use of thesitting position appeared to delay the spread of anesthesiato the midthoracic dermatomes. In comparison with thebolus administration of epidural local anesthetic, theextent of blockade may be more gravity dependent whenthe anesthetic is administered as a continuous infusionover a prolonged period.

Caudal anesthesia is used infrequently in modern obstet-ric anesthesia practice. However, there remain some cir-cumstances in which a caudal technique is useful and/oradvantageous. It is a good choice for the second stage oflabor in selected patients in whom the lumbar epiduralapproach is hazardous or contraindicated (e.g., fusion orinstrumentation of the lumbar spine). In most cases,caudal anesthesia can be successfully performed with thepatient in a lateral decubitus position. Anatomic variationmay require use of the knee-chest position in some patients.

ULTRASONOGRAPHIC GUIDANCETraditionally, surface anatomy visualization and palpationhave been used to assess landmarks prior to initiation of theneuraxial procedure. Anesthesia providers are now begin-ning to use ultrasonography as a tool to help assess neu-raxial anatomy. The use of ultrasonography has been shownto decrease both the number of attempts and the number ofbony contacts.26 In children, ultrasonography was shown toaid in verification of both local anesthetic spread and cath-eter placement.27 Color Doppler has also been used toassess epidural vascularity in parturients,28 and the skin–epidural space distance can be estimated.26,29 Unlike forvascular access and peripheral nerve block techniques,ultrasonography for neuraxial techniques is not utilized inreal time. Rather, it is a preprocedural tool to aid the oper-ator in the assessment of needle insertion site, needle angle,and estimated depth of the epidural space.

A low-frequency (2- to 5-Hz) curvilinear probe allows visu-alization of neuraxial structures beneath the skin. The ultra-sound beam can be used to identify first the spinous processesif these are not palpable, then the interspinous spaces, andfinally, ligamentous structures. The ligamentum flavum anddura mater are dense tissues and will appear hyperechoic, likebone, whereas the less dense epidural and subarachnoidspaces will appear hypoechoic (Figure 12-8). Transverse andmedian longitudinal as well as paramedian longitudinalapproaches have been documented. With the median longi-tudinal approach, the spinous process will produce a shadow


when the beam is placed directly over it, thus reducing theability to appreciate any ligaments beyond it.

Choice of Drug*

SPINAL ANESTHESIAAnesthesia providers may give spinal anesthesia for cer-clage, nonobstetric surgery during pregnancy, instrumentalvaginal delivery, cesarean delivery, removal of a retained pla-centa, or postpartum tubal ligation. Spinal analgesia may beused for labor analgesia. Cesarean delivery represents themost common indication for spinal anesthesia in pregnantwomen. Most anesthesia providers administer a hyperbaricsolution of local anesthetic for spinal anesthesia in obstetricpatients. Use of a hyperbaric solution results in a faster onsetof block and a higher maximum sensory level with a shorterduration of blockade.30 The urgency and anticipated dura-tion of surgery dictate the choice of local anesthetic agent.The most common choice in the United States is bupiva-caine. Other agents include lidocaine and tetracaine.Ropivacaine and levobupivacaine may be used but are not

approved for spinal administration in the United States,and levobupivacaine is not available in the United States.Lidocaine provides a short to intermediate duration ofaction. Bupivacaine, tetracaine, levobupivacaine, and ropiva-caine provide intermediate to long durations of action.

Anesthesia providers often add an opioid to the localanesthetic to improve the quality of anesthesia, particularlywith regard to visceral stimulation, and to provide post-operative analgesia.31,32 The addition of an opioid to thelocal anesthetic decreases the incidence of intraoperativenausea and vomiting.31 The short-acting, lipid-solubleopioids (i.e., fentanyl, sufentanil) contribute to intraopera-tive anesthesia, and morphine is often administered forpostoperative analgesia. Epinephrine may be added to pro-long block duration and perhaps improve block density.It was hoped that other adjuncts (e.g., clonidine, neostig-mine) might allow for the administration of a lower dose oflocal anesthetic and thereby minimize sympatholytic sideeffects and hasten recovery. Side effects from theseother adjuncts, however, have precluded their wide use inobstetric anesthesia practice (see Chapters 26 and 28).

EPIDURAL ANESTHESIALocal anesthetic agents available for epidural administrationin obstetric patients include 2-chloroprocaine, lidocaine,

Skin

SP

B

Sacrum

Skin

LF

AP

L5L4L3

VB

A

Skin

LF

AP

TP

VB

C

FIGURE 12-8 Ultrasonographic images of the lumbar spineobtained with use of a low-frequency curvilinear probe.A, Paramedian longitudinal plane. The typical ‘‘saw sign’’ isseen. The skin is at the top of the image. AP, articular process;LF, ligamentum flavum; VB, vertebral body. B, Transverse plane.The spinous process (SP) is seen as a hyperechoic signalimmediately beneath the skin (top of image), generating a longvertical acoustic shadow. C, Transverse plane. The elements ofthe interspace include midline structures such as the ligamentumflavum and the vertebral body, and paramedian structures suchas the transverse process (TP) and the articular process on eachside. (Images courtesy of Jose Carvalho, M.D.)

*Chapter 13 contains a detailed discussion of anesthetic agents

used for neuraxial anesthetic techniques.


mepivacaine, bupivacaine, ropivacaine, and etidocaine.Mepivacaine and etidocaine are used infrequently in obstet-ric anesthesia practice.

Bupivacaine remains the most popular local anestheticfor analgesia during labor and vaginal delivery because of itsdifferential sensory blockade, long duration of action,low frequency of tachyphylaxis, and low cost. Anesthesiaproviders infrequently administer bupivacaine for cesareandelivery because of the risk of cardiac toxicity and mater-nal mortality after unintentional intravascular injectionof the drug.

Ropivacaine has gained popularity as an agent for epi-dural analgesia and anesthesia because it may result in lesscardiac toxicity and greater differential sensory blockadethan bupivacaine.33 Levobupivacaine, although not avail-able in the United States, also has a more favorable safetyprofile than bupivacaine. Clinical trials have shown thatropivacaine and levobupivacaine have potency34 and anal-gesic qualities similar to those of bupivacaine,35,36 with theprobable exception of less motor nerve block.35,37

Bupivacaine, ropivacaine, and levobupivacaine all havelonger durations of action than lidocaine, and they maybe preferred over shorter-acting agents when longer dura-tion of anesthesia or analgesia is desirable. They are morecommonly used for maintenance of epidural labor analge-sia, whereas the shorter-acting agents are used for epiduralsurgical anesthesia. Despite some variation among reports,published clinical studies suggest no more than slight dif-ferences in onset and potency, and no differences in qualityor duration of neural blockade, among the three drugs.However, bupivacaine is more cardiotoxic than the otheragents in vitro and probably after unintentional intravascu-lar administration.38 It would seem prudent to use ropiva-caine or levobupivacaine rather than bupivacaine when abolus dose of a concentrated solution is being given. Whenadministered as a low concentration infusion, improvedsafety has not been demonstrated with ropivacaine andlevobupivacaine compared with bupivacaine.

The most popular choice of local anesthetic for epiduralanesthesia for cesarean delivery is 2% lidocaine with epi-nephrine. The addition of epinephrine (5 mg/mL) causes amodest prolongation of the block. The major advantage ofepinephrine is that it improves the quality of epidural lido-caine anesthesia. Lam et al.39 have shown that epidurallabor analgesia can be extended to surgical anesthesia forcesarean delivery in 5.2 ± 1.5 minutes with the addition ofbicarbonate and fentanyl to 2% lidocaine with epinephrine.

Many anesthesia providers reserve 2-chloroprocaine forcases in which rapid extension of epidural anesthesia forvaginal delivery or urgent cesarean delivery is necessary.The onset of surgical anesthesia was several minutes fasterwith 2-chloroprocaine compared with lidocaine with freshlymixed epinephrine and sodium bicarbonate in the setting ofurgent casarean delivery after epidural labor analgesia.40

Therefore, when time is of the essence, 2-chloroprocaine isthe drug of choice. Typically, in an emergency, a largevolume of concentrated local anesthetic solution is injectedquickly. An additional advantage of 2-chloroprocaine in thissituation is that it is rapidly metabolized by plasma esterases.Therefore, the unintentional intravascular injection of alarge volume of 2-chloroprocaine may be less likely to haveserious adverse consequences. A potential disadvantage of2-chloroprocaine is that it may interfere with the subsequent

actions of opioids41 and bupivacaine,42 although this possi-bility is controversial.43

As in spinal anesthesia, epidural opioids work synergis-tically with local anesthetics. Fentanyl 50 to 100 mg orsufentanil 5 to 10 mg is frequently added to an amidelocal anesthetic for both labor analgesia (allowing a lowerdose of local anesthetic and less motor block) and cesareandelivery (resulting in a denser block with better blockade ofvisceral stimulation). Sodium bicarbonate may be addedto lidocaine44 and 2-chloroprocaine45 (1 mEq/10 mL localanesthetic) to decrease latency.

CAUDAL ANESTHESIAThe drugs used for caudal epidural anesthesia are identicalto those used for lumbar epidural block. However, a muchlarger volume (e.g., 25 to 35 mL) of local anesthetic solutionmust be administered to extend a caudal block for cesareandelivery or labor analgesia. Such large volumes entail agreater risk of systemic local anesthetic toxicity.

Equipment and Needle and Catheter Placement

SPINAL ANESTHESIAThe first equipment decision involves determining whetherto perform a single-shot or continuous technique.Continuous spinal anesthesia is not a new technique;indeed, some physicians gave continuous spinal anesthesia50 years ago. Currently, a large-bore epidural needle andcatheter must be used for continuous spinal anesthesia,because the U.S. Food and Drug Administration rescindedapproval for the use of small-bore catheters in 1992.46

Therefore, the risk of post–dural puncture headache is sig-nificant. This technique is useful after unintentional duralpuncture with an epidural needle. In the morbidly obesepatient, it may be easier to manipulate and advance arigid epidural needle than a more flexible spinal needle;thus, the technique is useful for establishing continuousanalgesia or anesthesia in this patient population, particu-larly when the need for anesthesia is urgent. However, formost obstetric patients, a single-shot technique is preferredfor spinal anesthesia.

The primary equipment choice for spinal anesthesia con-cerns the type and size of the spinal needle. Cutting-bevelneedles (e.g., Quincke) are rarely used in obstetric anesthesiapractice today because of the unacceptably high incidenceof post–dural puncture headache associated with theiruse.47 Instead, non-cutting needles (e.g., Whitacre, Sprotte,Greene) are used almost exclusively (Figure 12-9). Someanesthesia providers refer to the Whitacre and Sprotte nee-dles as ‘‘pencil-point needles.’’ It is now believed that thepencil-point needles cause more trauma to the dura, whichthen results in a more intense inflammatory response thanoccurs with cutting-bevel needles. Presumably, the inflam-mation results in edematous closure of the dural defect.48

Needle size must also be determined. In general, the‘‘ease-of-use’’ advantages associated with larger needlesmust be balanced against a lower incidence of post–duralpuncture headache with smaller needles. For most anesthe-sia providers, the two curves cross at the use of a 25-gaugeneedle (i.e., with smaller needles, the technical difficultiesincrease enough to offset the small reduction in the inci-dence of post–dural puncture headache). However, anes-thesia providers should make individual decisions based on


their own skills, practice setting, and patient. The urgencyof the procedure may also influence the choice of needlesize. For example, a 27-gauge needle might be chosen forspinal anesthesia for an elective procedure, and a larger(e.g., 22-gauge) needle might be chosen when the subarach-noid space must be entered quickly because of severe fetalcompromise.

With a small-gauge needle (i.e., 24-gauge or smaller),use of an introducer needle is preferable. The introducerneedle allows for more accurate introduction of the spi-nal needle than is possible with use of a small-gaugespinal needle alone. The introducer needle also aidswith skin puncture; it is often difficult to puncture theskin with non-cutting needles.

Either the midline or the paramedian approach can beused to enter the subarachnoid space. The midlineapproach requires the patient to reduce her lumbar lordosisto allow access to the subarachnoid space between adjacentspinous processes (usually L3 to L4, sometimes L4 to L5 orL2 to L3). The interspinous space may be identified withone (usually the thumb or index finger) or two fingers(usually the index and middle fingers) of the anesthesiaprovider’s nondominant hand. The single finger ‘‘slides’’along the skin in the midline from cephalad to caudaduntil it ‘‘settles’’ into an interspinous space. The two fingersidentify the interspinous space by palpating the caudadborder of the more cephalad spine. The fingers identifythe midline by rolling in a medial-to-lateral direction(Figure 12-10). Next, the anesthesia provider injects localanesthetic intradermally and subcutaneously. The intro-ducer needle is inserted into the substance of the interspi-nous ligament. It is helpful if the introducer needle isembedded in the interspinous ligament; therefore, obesepatients may require a longer needle. The introducerneedle should lie in the sagittal midline plane. It is thengrasped and steadied with the fingers of the nondominanthand while the dominant hand holds the spinal needle like adart. The fifth finger may be used as a tripod against thepatient’s back to prevent patient movement from causing

FIGURE 12-9 Spinal needle assortment often used in parturients. Each needle is shown in an open-bevel view and an oblique orientation.The Whitacre and Sprotte needles have cone-shaped bevels, whereas the Quincke has a cutting bevel. (Other sizes are available insome of these needle designs.)

Palpate medial-to-lateraland cephalad-to-caudad

Introducerinsertion

Spinal needleinsertion

FIGURE 12-10 The midline approach for spinal needle insertionrequires accurate identification of a lumbar interspinous space.The palpating fingers are rolled in a medial-to-lateral andcephalad-to-caudad direction; an introducer is then insertedthrough the interspinous space almost perpendicular to the lumbarspinous process. Once the introducer is seated in the interspinousligament, the spinal needle is inserted; the needle is stabilized ina tripod fashion during insertion (much like a dart being thrown).


unintentional needle insertion to a level deeper thanintended, and to ‘‘brake’’ the needle. As the needle passesthrough the ligamentum flavum and the dura, characteristicchanges in resistance are noted. A ‘‘pop’’ is often perceivedas the needle tip traverses the dura mater. The stylet isremoved, and CSF should appear in the needle hub. IfCSF does not appear, the stylet is replaced, and theneedle is advanced a few millimeters and again checkedfor CSF flow. If CSF does not appear at this point andthe needle is at an appropriate depth for the patient,the needle and introducer are withdrawn, and the processis repeated.

The most common reason for lack of CSF flow is inser-tion of the needle away from the midline. If the anesthesiaprovider achieves good anesthesia of the skin and subcuta-neous tissues, correct use of the midline approach is almostpainless. Significant pain suggests that the needle is directedaway from the midline; indeed, a patient often indicates thatthe pain is localized to either the left or right side of themidline. In such cases, correct direction of the needle shouldbe confirmed. Redirection of the needle often eliminates thepatient’s pain and results in the successful identification ofthe subarachnoid space.

Needle contact with bone also mandates redirection ofthe needle. If the needle is in the midline, the bone is eitherthe cephalad or caudad spinous process, and the needleshould be angled up or down in the sagittal midlineplane. If the needle tip is angled off the midline or punc-tures the skin off the midline, the bone is probably thelamina of the vertebral arch. Needle contact with bone isusually painful. Again, the patient is often able to articulatewhether she feels pain on the right or left side, or in themidline, allowing the anesthesia provider to make needleadjustments in the appropriate direction.

Once CSF is freely dripping from the needle hub, thedorsum of the provider’s nondominant hand steadies thespinal needle against the patient’s back while the syringewith local anesthetic is attached to the needle. After aspir-ating to ensure the free flow of CSF, the anesthesia pro-vider injects the local anesthetic at a rate of approximately0.2 mL per second. After completion of the injection, the

anesthesia provider again aspirates approximately 0.2 mLof CSF and reinjects it into the subarachnoid space. Thislast step reconfirms the needle location and clears theneedle of the remaining local anesthetic. The patient isthen repositioned as appropriate.

For most patients, the midline approach is faster and lesspainful than the paramedian approach. The midlineapproach is also easier to teach than the paramedianapproach, because it requires mental projection of the anat-omy in only two planes, whereas the paramedian approachrequires appreciation of a third plane and estimation ofthe depth of the subarachnoid space from the skin(Figure 12-11). Nevertheless, the paramedian approach isa useful technique that allows for the successful identifica-tion of the subarachnoid or epidural space in difficult cases.The paramedian approach does not require that the patientfully reduce her lumbar lordosis. This approach exploits thelarger target that is available when the needle is insertedslightly off the midline.

A common error that is made with the paramedianapproach is the insertion of the needle too far off the mid-line; the vertebral lamina then becomes a barrier to needleinsertion. With the paramedian approach, the palpatingfingers should again identify the caudad edge of the morecephalad spinous process. A skin wheal is raised 1 cm lat-eral and 1 cm caudad to this point; a longer needle is thenused to infiltrate the deeper tissues in a cephalomedialplane. This step contrasts with the midline approach, inwhich the local anesthetic is not injected beyond the sub-cutaneous tissue. The spinal introducer is then inserted10 to 15 degrees off the sagittal plane in a cephalomedialdirection, and the spinal needle is advanced through theintroducer needle toward the subarachnoid space.Another common error is to use an excessive cephaladangle with initial needle insertion. When the needle isinserted correctly and contacts bone, it is redirected slightlycephalad. If bone is again encountered, but at a deeper level,the slight stepwise increase in cephalad angulation is con-tinued, and the needle is ‘‘walked’’ up and off the lamina.As with the midline approach, the characteristic feel of theligamentum flavum and dura can be appreciated. The aim

L3

10°–15°

1 cm

1 cmFIGURE 12-11 Vertebral anatomy of midline and paramedianapproaches for spinal and epidural anesthesia. The midlineapproach requires anatomic projection in only two planes,sagittal and horizontal. The paramedian approach alsorequires consideration of the oblique plane. However, theparamedian approach requires less patient cooperation inreducing lumbar lordosis to allow for successful needleinsertion. The paramedian needle insertion site is made 1 cmlateral and 1 cm caudad to the caudad edge of the morecephalad spinous process. The paramedian needle is insertedapproximately 10 to 15 degrees off the sagittal plane (inset).


of the paramedian approach is to puncture the dura in themidline, even though the needle is inserted off the midline.Use of the paramedian approach requires insertion of agreater length of needle. Once CSF is obtained, the blockis performed as it is with the midline approach.

The Taylor approach is a variation of the paramedianapproach using the L5 to S1 interspace, which has the larg-est interlaminar space in the lumbosacral region. A 5-inchspinal needle is inserted in a cephalomedial plane from asite 1 cm medial and 1 cm caudad to the lowermost prom-inence of the posterior superior iliac spine. If bone isencountered on the first needle insertion, the needle isredirected in small steps cephalad to walk off the sacrumand into the subarachnoid space.

During the performance of any nerve block technique,needle advancement should stop if the patient complains ofpain. If pain is the result of inadequate soft tissue anesthe-sia, additional local anesthetic should be injected. Pain orparesthesias may also result from needle contact with cen-tral nerves or the spinal cord. Patient perception of par-esthesias during the initiation of spinal anesthesia mayindicate that the needle tip is in the subarachnoid space.The anesthesia provider should remove the stylet and checkfor CSF. If the paresthesia has resolved, the local anestheticmay be injected. If the paresthesia persists, however, theneedle should be withdrawn and repositioned. In anycase, the anesthesia provider should never inject the localanesthetic if the patient is complaining of paresthesias orlancinating pain, either of which may signal injection into anerve or the spinal cord.

EPIDURAL ANESTHESIASpecial equipment for epidural analgesia or anesthesiaincludes an epidural needle, an epidural catheter (for a con-tinuous technique), and a loss-of-resistance syringe (for theloss-of-resistance technique to identify the epidural space).Single-shot epidural anesthesia is rarely used in obstetricpractice, because the major advantage of epidural overspinal anesthesia is the ability to provide continuous anes-thesia or analgesia without puncturing the dura with a largeneedle. Most anesthesia providers use the loss-of-resistancetechnique to identify the epidural space; therefore a syringeis necessary. An epidural needle with a lateral opening (e.g.,Hustead, Tuohy) is most commonly used because it allows acatheter to be threaded through its orifice (Figure 12-12).

Several types of single-use, disposable epidural cathetersare available. Catheters are made from plastic materials anddiffer as to the degree of ‘‘stiffness.’’ Wire-embedded cathe-ters are more flexible and are associated with a lower inci-dence of paresthesias and intravascular placement duringcatheter insertion.49,50 The single-orifice catheter has oneopening at its tip, whereas the multi-orifice catheter has aclosed ‘‘bullet’’ tip with 3 lateral orifices between 0.5 and1.5 cm from the tip (Figure 12-13). The proposed advantageof single-orifice, open-end catheters is that the injection ofdrugs is restricted to a single anatomic site. In theory, thisarrangement should facilitate the detection of intravenousor subarachnoid placement of the catheter. Likewise, atheoretical disadvantage of multi-orifice, closed-end cathetersis that local anesthetic may be injected into more than oneanatomic site (e.g., both the epidural and subarachnoidspaces). A catheter initially placed in the epidural space canmigrate into a vein or the subdural or subarachnoid space.

Fortunately, this does not seem to be a common clinicalproblem. Regardless of the choice of catheter, aspirationshould be performed before each dose of local anesthetic isinjected.

An advantage of the multi-orifice catheter over thesingle-orifice catheter is the consistent ability to aspiratefluid (either blood or CSF) when the catheter is in avessel or the subarachnoid space.51 Multi-orifice cathetersmay lead to more even distribution of local anesthetic and alower incidence of ‘‘patchy’’ or unilateral anesthesia whenthe anesthetic is injected as a bolus.52 However, during aninfusion into the epidural space, the solution exits only themost proximal hole,53 and multi-orifice catheters thusbehave like single-orifice catheters.

FIGURE 12-12 Epidural needles often used in parturients. Eachneedle is shown in an open-bevel view and an oblique orientation.The 18-gauge Hustead and 17-gauge Tuohy needles have lateral-facing openings, which direct epidural catheters to enter the epiduralspace more easily than if a single-shot Crawford needle design is used.(Other sizes and needle designs are available for obstetric epiduralanesthesia.)

A B C

15cm 20cm10cm

FIGURE 12-13 Epidural catheters. A, Single-orifice catheter;B, multi-orifice catheter with bullet tip; C, coiled wire reinforcedcatheter. Bottom, Epidural catheter with centimeter markings alongdistal end and Luer-Lok connector at proximal end. (Drawing byNaveen Nathan, M.D., Northwestern University Feinberg Schoolof Medicine, Chicago, IL.)


Two methods are used to identify the epidural spaceduring needle advancement: (1) hanging drop methodand (2) loss-of-resistance method. The majority ofanesthesia providers use the loss-of-resistance method(Figure 12-14). The traditional loss-of-resistance syringe isa finely ground glass syringe with a Luer-Lok connector.Plastic syringes are now available, and the choice is gener-ally a matter of the anesthesia provider’s preference. Thesyringe is filled with 2 to 4 mL of saline, air, or saline with asmall air bubble. There is some controversy regarding theuse of air versus saline for detecting the point of loss ofresistance.54 Saline causes some syringe plungers to stickand may be confused with CSF during initiation of com-bined spinal-epidural anesthesia. Conversely, injection ofair into the epidural space may contribute to patchyanesthesia,55 and unintentional pneumocephalus mayincrease the risk of post–dural puncture headache.56 Weprefer that the syringe contain both saline and a small(e.g., 0.25 mL) compressible bubble of air, although manyanesthesia providers successfully use air.

Regardless of the technique used, success depends oncorrect placement of the needle tip within the ligamentumflavum. The needle should be advanced well into the inter-spinous ligament, or even into the ligamentum flavum,before the syringe is attached or before the hanging dropof solution is placed into the needle hub. This approach hasat least three advantages. First, it encourages the anesthesiaprovider to use proprioception while directing and advan-cing the needle. Second, it shortens the time required forsuccessful identification of the epidural space. Third, itlowers the likelihood of a false-positive loss of resistance.

Undoubtedly, this false-positive identification of the epidu-ral space is responsible for many cases of unsuccessful epi-dural anesthesia; it is even possible to insert a catheterbetween the interspinous ligament and the ligamentumflavum.

During advancement of the needle-syringe assembly, theneedle should be moved toward the epidural space bythe provider’s nondominant hand while the thumb of thedominant hand applies constant pressure on the syringeplunger, thereby compressing the 0.25-mL air bubble.Alternatively, the intermittent, oscillating technique istypically employed when using loss of resistance to air.When the needle enters the epidural space, the pressureapplied to the syringe plunger causes the solution or airto flow easily into the epidural space (see Figure 12-14).

In most obstetric cases, the anesthesia provider inserts acatheter and uses a continuous technique. The providermust decide whether to insert the catheter before or afterthe test and therapeutic doses of local anesthetic. Mostpractitioners insert the catheter before injecting local anes-thetic, to allow for the slow, incremental injection of localanesthetic and the more controlled development of epiduralanesthesia. However, there is little evidence that the incre-mental injection of local anesthetic through the catheterresults in less significant hemodynamic change than incre-mental injection through the needle (followed by insertionof the catheter); also, injection through the needle mayshorten the time to complete anesthesia or analgesia.Nonetheless, if the principal reason for using an epiduraltechnique is the provision of continuous analgesia, it seemsmost practical to insert the catheter before injecting the

Compressedair bubble

L3

L3

L4

L4

FIGURE 12-14 Loss-of-resistance technique for identifying theepidural space. The needle is first inserted into the interspinousligament or ligamentum flavum, and a syringe containing an airbubble in saline is attached to the hub. After compression of theair bubble by pressure on the syringe-plunger, the needle iscarefully advanced until a loss of resistance to syringe-plungerpressure is noted as the needle enters the epidural space.


therapeutic dose of local anesthetic so that correct catheterplacement can be verified promptly. Alternatively, bothtechniques can be combined, in that a small dose of localanesthetic is injected through the needle and the remainderof the dose is injected through the catheter.

If the catheter is placed before the test and therapeuticdoses of local anesthetic, it may be helpful to inject 5 to10 mL of saline before threading the catheter, as this mayreduce the incidence of epidural vein cannulation,57,58 par-ticularly when using stiffer epidural catheters. Rolbin et al.59

noted that there was no advantage to the injection of 3 mLof fluid into the epidural space before insertion of the epi-dural catheter.

Six to eight centimeters of catheter are threaded intothe epidural space before the epidural needle is removed.The catheter may then be pulled back until it is at thedesired distance at the skin. Occasionally, the anesthesiaprovider will have difficulty advancing the catheter pastthe tip of the epidural needle. This difficulty may indicatethat the epidural needle tip is not in the epidural space.However, if the provider is convinced that the needle iscorrectly placed, several maneuvers may facilitate catheteradvancement. Often, having the patient take a deep breathallows catheter advancement. Saline may be injectedthrough the epidural needle if this has not been done.Although some providers rotate the epidural needle inan attempt to successfully advance the catheter, we donot recommend this maneuver, because it may increasethe risk of dural puncture. Instead, the epidural needleshould be withdrawn 0.5 to 1 cm, and again advancedinto the epidural space.

Many techniques are available for securing the epiduralcatheter at the skin entry site. If a catheter will be used forprolonged intrapartum or postoperative analgesia, careproviders should be able to assess the skin surroundingthe catheter. A transparent, sterile adhesive dressingapplied over the catheter after application of skin adhesivegenerally works well, and the periphery of the dressing canbe reinforced with tape. The position of the epidural cath-eter may change significantly with patient movement fromthe sitting-flexed to the sitting-upright or lateral decubitusposition.60 D’Angelo et al.61 found that the risk of catheterdislodgement was higher when catheters were inserted2 cm into the epidural space, but the risk of unilateralblockade was higher when catheters were inserted 6 to8 cm. Therefore, if the catheter is to be used for a shortperiod (e.g., cesarean delivery), it should be left 2 to 4 cminto the epidural space. In contrast, if the catheter will beused for many hours (e.g., labor), it should be left 4 to6 cm into the space. To minimize catheter movementat the skin, the patient should be positioned sittingupright or in the lateral position before the catheter issecured.60

The potential for the contamination of local anestheticsolutions has prompted the use of micropore filters duringthe administration of continuous epidural anesthesiafor labor. There is no evidence that filters decreasethe rate of infection or of injection of undesirable for-eign substances.62 Additionally, filters may reduce thereliability of aspiration63 and absorb local anesthetic solu-tion, unless they are primed.64 We believe that microporefilters have little utility in clinical obstetric anesthesiapractice.

COMBINED SPINAL-EPIDURAL ANESTHESIACombined spinal-epidural (CSE) anesthesia combines theadvantages and mitigates the disadvantages of single-shotspinal anesthesia and continuous epidural anesthesia(Box 12-1). Anesthesia is initiated with a subarachnoid injec-tion of local anesthetic and maintained via an epidural cath-eter. It is useful for both cesarean delivery anesthesia andlabor analgesia. The injection of the smaller dose of localanesthetic required for spinal (compared with epidural)anesthesia is inherently safer with regard to the possibilityof unintentional intravascular injection. Additionally, theanesthesia provider can inject a local anesthetic dose thatis lower than the ED95 (effective dose in 95% of cases) with-out fear of inadequate anesthesia. If surgical anesthesia isinadequate, the block can be ‘‘rescued’’ with epidural admin-istration of local anesthetic. Lower intrathecal local anes-thetic doses reduce the risk of maternal hypotension.65

Compared with conventional epidural anesthesia for cesar-ean delivery, CSE anesthesia is associated with a more rapidonset of surgical anesthesia, less intraoperative pain and dis-comfort (e.g., a more dense block), better muscle relaxation,and less shivering and vomiting.66

During labor, CSE analgesia is associated with a fasteronset of analgesia.67 Studies differ as to whether CSE anal-gesia is associated with higher maternal satisfaction andfewer requests for supplemental analgesia. A 2007 system-atic review comparing CSE analgesia with epidural laboranalgesia concluded that onset was faster with the CSEtechnique but that there was no evidence for differencesin maternal satisfaction, mode of delivery, ability to ambu-late, or incidence of hypotension between the two tech-niques.68 Several studies have found a lower incidence offailed epidural analgesia after the initiation of analgesiawith a CSE technique.69,70 Presumably, verification of the

BOX 12-1 Advantages of Combined Spinal-EpiduralAnesthetic Technique

Compared with Epidural Anesthesia� Lower maternal, fetal, and neonatal plasma

concentrations of anesthetic agents� More rapid onset of analgesia and anesthesia� More dense sensory blockade� Complete early labor analgesia with opioid alone

(no local anesthetic necessary)� Lower failure rate

Compared with Spinal Anesthesia� Technically easier in obese individuals: The epidural

needle acts as an introducer for the spinal needle (it iseasier to advance a rigid epidural needle).

� Ability to titrate anesthetic dose (Start with lowsubarachnoid dose, and titrate to effect using epiduralinjection.)

� Results in less hypotension� Ability to extend the extent of neuroblockade

(Spinal anesthesia for forceps delivery may be extendedto epidural anesthesia for cesarean after failed forcepsdelivery.)

� Continuous technique: ability to extend duration ofanesthesia


correct placement of the spinal needle by visualization ofCSF increases the likelihood that the tip of the epiduralneedle is correctly placed in the epidural space.

A disadvantage of the CSE technique is that the correctplacement of the epidural catheter in the epidural spacecannot be verified until spinal anesthesia wanes.Therefore, if a functioning epidural catheter is importantto the safe care of the mother and fetus (e.g., in the settingof a suspected difficult airway or nonreassuring fetal status),a CSE technique is not the technique of choice.

There are several techniques for CSE anesthesia.71 Themost popular is the needle-through-needle technique, inwhich the epidural needle is sited in the epidural spaceand serves as an introducer for the spinal needle. Thespinal needle passes through the epidural needle to punc-ture the dura. After injection of the intrathecal dose, thespinal needle is removed and the epidural catheter isthreaded through the epidural needle. An alternative tech-nique uses two skin punctures and two different inter-spaces: The spinal needle and epidural needle andcatheter are introduced sequentially in two differentinterspaces.

The needle-through-needle technique requires a longspinal needle. Typically, a small (25-gauge or smaller)non-cutting needle is used in order to minimize the riskof post–dural puncture headache. The tip of the spinalneedle must protrude 12 to 17 mm beyond the tip of theepidural needle when the two needles are fully engaged(Figure 12-15). Failure to puncture the dura and visualizeCSF occurred in 25% of patients when the spinal needleprotruded 9 mm, compared with no patients when theneedle protruded 17 mm.72 A 127-mm spinal needle iscommonly used with a standard 9-cm epidural needle.However, because of differences in hub configurationsamong needles, the two hubs may not ‘‘mesh,’’ and spinalneedle protrusion may vary with specific needle combina-tions. Alternatively, manufacturers now sell CSE needle‘‘kits,’’ in which the spinal needle is designed for a specificepidural needle. An additional small non–Luer-Lok syringe(1 to 3 mL) is required for the spinal dose.

CSE anesthesia is initiated much like epidural anesthe-sia. The epidural needle is sited in the epidural space(Figure 12-16). The spinal needle is introduced throughthe epidural needle with the anesthesia provider’s domi-nant hand, while the nondominant hand is anchoredagainst the patient’s back to serve as a brake for furtheradvancement of the spinal needle. The provider usuallyperceives the tip of the spinal needle passing the tip ofthe epidural needle as a slight increase in resistance. Spinalneedle advancement should stop immediately after theanesthesia provider perceives the dural puncture ‘‘pop.’’Dural puncture is verified by visualization of CSF afterremoval of the spinal needle stylet. The provider’s non-dominant hand is anchored on the patient’s back, and thespinal and epidural needle hubs are grasped togetherbetween the thumb and index finger of this hand. Thedominant hand attaches the spinal syringe and injectsthe drug. We do not attempt to aspirate CSF, because itmay not be possible to do so through long, small-boreneedles and because attempted aspiration may result inmovement of the spinal needle. After removal of thespinal syringe and needle as a unit, the epidural catheteris threaded in the usual fashion.

Failure to puncture the dura with the spinal needle mayoccur in several circumstances (Figure 12-17). The epiduralneedle tip may not be located in the epidural space, or theneedle tip may be correctly placed, but the spinal needlemay fail to puncture the dura or may not reach the durabecause of the depth of the posterior epidural space.Alternatively, the epidural needle may be angled awayfrom the midline or in a sagittal plane off the midline,and the spinal needle may traverse the lateral epiduralspace without puncturing the dura. In this latter circum-stance, the anesthesia provider may elect to abandon theCSE technique and continue with epidural anesthesia(if convinced that the epidural needle tip is in the epiduralspace) or to reposition the epidural needle and reattemptthe CSE technique.

CAUDAL ANESTHESIAEquipment for caudal anesthesia is similar to that used forlumbar epidural techniques, except that a needle with alateral-faced opening is not needed. A blunt-tipped needleis satisfactory even when a catheter is used, because theangle of needle insertion allows insertion of the catheter.Successful administration of caudal anesthesia requires theaccurate identification of the sacral hiatus. The sacrococcy-geal ligament (an extension of the ligamentum flavum)overlies the sacral hiatus between the sacral cornua.Identification of the posterior superior iliac spines facilitates

FIGURE 12-15 Combined spinal-epidural needle configuration.Top, Spinal needle exits the epidural needle through the normalepidural needle bevel. Because the epidural needle bevel openingfaces sideways, the spinal needle exits the epidural needle at a slightangle to the long axis of the epidural needle. Bottom, Spinal needleexits the epidural needle through a special orifice. The axes of thespinal and epidural needles are aligned. The spinal needle mustprotrude from the tip of the epidural 12 to 17 mm when the hubsare engaged, or the ability to puncture the dura with the spinal needleis compromised. (Drawing by Naveen Nathan, M.D., NorthwesternUniversity Feinberg School of Medicine, Chicago, IL.)


A C

B D

FIGURE 12-16 Needle-through-needle combined spinal-epidural technique. A, The epidural needle is sited in the epidural space. B, The longspinal needle is passed through the epidural needle and punctures the dura mater. C, The operator’s nondominant hand stabilizes the spinal andepidural needles, and the spinal needle stylet is withdrawn. Cerebrospinal fluid is seen spontaneously dripping from the spinal needle. D, Thesyringe is attached to the spinal needle, and the intrathecal dose is injected.

Continued


the identification of the sacral cornua; the location of thesacral hiatus is approximated by using the line betweenthem as one side of an equilateral triangle (Figure 12-18).Once the sacral hiatus is identified, the palpating fingers areplaced on the cornua, the skin is anesthetized, and thecaudal needle is inserted with the hub at an angle approx-imately 45 degrees from the skin. A decrease in resistance isnoted when the needle enters the caudal canal. The needleis advanced until it contacts bone (i.e., the dorsal aspect ofthe ventral plate of the sacrum). Next, the needle is with-drawn slightly and redirected so that the angle of insertionrelative to the skin surface is decreased. In pregnantwomen, the final angle is approximately 15 degrees froma plane parallel to the sacrum.

Accurate placement of the caudal needle is verifiedprimarily from the ‘‘feel’’ of the needle passing throughthe sacrococcygeal ligament. An additional maneuver mayhelp providers with less experience to verify correctneedle placement: Once the needle is believed to bewithin the caudal canal, 5 mL of saline is rapidly injectedthrough the needle while the anesthesia provider’s otherhand is placed over the dorsum of the sacrum. If theneedle is placed correctly, no mass or pressure wave isdetected over the midline of the sacrum. Conversely, ifthe needle is malpositioned (often posterior to the cau-dal canal), a fluid mass or pressure wave is felt by thepalpating hand.

The needle should be advanced only 1 to 2 cm into thecaudal canal. Dural puncture or unintentional intravascularcannulation is more likely to occur with deeper insertion.A test dose similar to that used during administration oflumbar epidural anesthesia should be administered.

COMPLICATIONS OF NEURAXIAL TECHNIQUES

Unintentional Dural Puncture

Unintentional dural puncture with an epidural needleoccurs at a rate of approximately 1.5% in the obstetric pop-ulation.73 Approximately 52% of women will experience apost–dural puncture headache after puncture with an epi-dural needle. Techniques to minimize the incidence ofunintentional dural puncture include the following: (1) iden-tification of the ligamentum flavum during epidural needleadvancement; (2) understanding the likely depth of theepidural space in an individual patient; (3) advancementof the needle between contractions, when unexpectedpatient movement is less likely; (4) adequate control ofthe needle-syringe assembly during advancement of theneedle; and (5) clearing the needle of clotted blood orbone plugs. Norris et al.74 observed that post–dural punc-ture headache after unintentional dural puncture was lesslikely to result in headache if the epidural needle bevel facedlateral rather than cephalad. In contrast, Richardson et al.75

found no difference between the two orientations. An invitro study using cadaver dura found that fluid leakage ratethrough dural tears was not dependent on the orientation ofthe dura relative to the needle bevel.76 We prefer to insertthe epidural needle with the bevel oriented in a cephalad

E

FIGURE 12-16 cont’d E, The spinal needle is withdrawn, and theepidural catheter is threaded through the epidural needle into theepidural space. (Drawing by Naveen Nathan, M.D., NorthwesternUniversity Feinberg School of Medicine, Chicago, IL.)

Ligamentumflavum

Spinalneedle

Dura

Ligamentumflavum

Spinalneedle

Dura

Ligamentumflavum

Spinalneedle

Dura

A B C

FIGURE 12-17 Reasons for failure of the combined spinal-epidural technique. A, The spinal needle tents the dura but does not puncture it.B, The spinal needle does not reach the dura. C, The spinal needle passes to the side of the dural sac. (Redrawn with permission from Riley ET,Hamilton CL, Ratner EF, Cohen SE. A comparison of the 24-gauge Sprotte and Gertie Marx spinal needles for combined spinal-epidural analgesiaduring labor. Anesthesiology 2002; 97:574.)


direction so that there is no need to rotate the needle bevelwithin the epidural space. Cephalad bevel orientationalso increases the likelihood of successful epiduralanesthesia.75,77

The management of unintentional dural puncturedepends on the clinical setting. One option is to site theepidural catheter within the subarachnoid space and to usea continuous spinal anesthetic technique. Evidence is con-flicting as to whether the insertion of an epidural catheterthrough the dural puncture site decreases the incidence of

post–dural puncture headache.78-80 Continuous spinalanesthesia is an attractive option if identification of theepidural space has been difficult, or if the anticipated dura-tion of epidural anesthesia or analgesia is relatively short(e.g., cesarean delivery, or vaginal delivery in parouswomen). The major disadvantage of an intrathecal catheteris the risk that it may be mistaken for an epidural catheter.Given that the local anesthetic dose required for epiduralanesthesia is many times greater than that required forspinal anesthesia, unintentional administration of an epidu-ral dose into the subarachnoid space will lead to total spinalanesthesia. Therefore, on a busy labor and delivery unitwhere multiple providers are giving anesthesia care, itmay be safer to use an epidural catheter rather than anintrathecal catheter in women in whom prolonged analge-sia is anticipated.

The new catheter should be placed in another lumbarinterspace, if possible. Even if the second catheter is cor-rectly placed in the epidural space, anesthesia providersmust be wary of an unexpectedly high level of anesthesiaafter administration of usual doses of local anesthetic.81,82

Leach and Smith82 reported a patient who had an extensiveblock after unintentional dural puncture and subsequentepidural injection of bupivacaine. They presented radiologicevidence of the spread of local anesthetic from the epiduralspace to the subarachnoid space. The extent to which adural tear affects the movement of substances from theepidural space to the subarachnoid space depends on thesize of the hole, the lipophilicity of the drug (highly lipo-philic drugs cross quickly regardless of the presence of ahole, whereas water-soluble drugs cross more quickly in thepresence of a hole),83 and whether the drug is administeredinto the epidural space as a bolus or an infusion.

Unfortunately, there is no reliable method to decreasethe risk of post–dural puncture headache once dural punc-ture occurs. Obese patients appear to be at lower risk forthe development of headache.84 A prophylactic blood patch(injection of autologous blood before removal of the epidu-ral catheter and before onset of a headache) does notreduce the risk of post–dural puncture headache.85

Unintentional Intravascular or Subarachnoid Injection

The unintentional injection of drugs into blood vessels or thesubarachnoid space can lead to catastrophe. The incidenceof intravascular catheter placement varies according tocatheter type,49 patient population,86 and proper placementof the epidural needle tip in the midline. Pregnant womenare at higher risk for unintentional intravenous cannulation.Because the unintentional intravascular or subarachnoidinjection of large doses of local anesthetic can be life-threatening, several precautions should be taken to reducethe chances and risks of intravascular injection. Theseinclude aspiration before each injection, incrementaladministration of small amounts of drug, use of an infu-sion when appropriate, and administration of an epiduraltest dose.

EPIDURAL TEST DOSEThe purpose of the test dose is to help identify uninten-tional cannulation of a vein or the subarachnoid space. Thetest dose should contain a dose of local anesthetic and/oranother marker sufficient to allow the recognition of

1

2

3 Insertion45°

15°

FIGURE 12-18 The location of the sacral hiatus for caudal anesthesiais facilitated by the identification of the posterior superior iliac spines.The posterior superior spines are marked, and a line drawn betweenthem forms one edge of an equilateral triangle. If the triangle iscompleted as illustrated, the sacral hiatus should underlie the caudadtip of the equilateral triangle. Inset, Once the sacral hiatus isidentified, the needle is inserted by insertion and withdrawal in astepwise fashion from an initial 45-degree angle off the coronal plane.In pregnant women, the needle eventually enters the caudal canal atan angle approximately 15 degrees off the coronal plane. If theneedle is placed properly, no subcutaneous ‘‘lump’’ develops after theinjection of the local anesthetic solution. (Redrawn from Brown DL.Spinal, epidural, and caudal anesthesia. In Miller RD, editor.Miller’s Anesthesia. 6th edition. Philadelphia, Churchill Livingstone,2005:1653.)


intravenous or subarachnoid injection but not so large as tocause systemic toxicity or total spinal anesthesia. The mostcommon intravascular test dose contains epinephrine, asrecommended by Moore and Batra.87 Intravenous injectionof epinephrine 15 mg consistently causes a transientincrease in heart rate during the first minute after injectionin nonpregnant subjects.

The epinephrine test dose is not without detractors.Some anesthesia providers fear that intravenous injectionof epinephrine may decrease uteroplacental perfusion andprecipitate fetal compromise.88-90 Counterargumentsinclude the fact that changes in uterine blood flow afterintravenous injection of epinephrine in pregnant laboratoryanimals were transient.88 Similar transient declines in per-fusion undoubtedly occur during normal uterine contrac-tions, and the adverse maternal and fetal consequences ofintravenous injection of a large therapeutic dose of localanesthetic would likely be more severe. There has beenno report of adverse neonatal outcome after intravenousinjection of an epinephrine-containing test dose.

The epinephrine test dose is less specific in laboringwomen because cyclic changes in maternal heart rate com-plicate interpretation of its effects.91,92 For this reason, thetest dose should be given immediately after a uterine con-traction so there is less confusion as to whether tachycardiais caused by pain or intravenous epinephrine.93 Anotherargument against routine use of a test dose is that aspirationof multi-orifice catheters is 98% sensitive in identifyingtheir intravascular location.51 Finally, because modern epi-dural labor analgesia involves the infusion of a low concen-tration of local anesthetic, unintentional intravascularadministration is not likely to result in cardiovascularcollapse.

Others argue that the epinephrine test dose still has arole in obstetric anesthesia practice.94 Large volumes of aconcentrated local anesthetic solution are still routinelyadministered for urgent cesarean delivery. Lee et al.95 sum-marized injuries associated with regional anesthesia inthe American Society of Anesthesiologists (ASA) Closed-Claims Database and identified unintentional intravascularinjections as the second most common damaging event inobstetric claims. All events were associated with epidural orcaudal anesthesia, and 75% resulted in cardiac arrest.Although a test dose was used in the majority of cases,only 30% of the test doses contained epinephrine.

Other methods of detecting intravascular injection arethe injection of subtoxic doses of local anesthetic and theinjection of isoproterenol,96,97 a small volume of air,98 orfentanyl99,100 (Table 12-2).

It is imperative that the anesthesia provider take the timeto look for evidence of intrathecal injection of local anes-thetic. Intrathecal injection of lidocaine 30 to 45 mg orbupivacaine 5 to 7.5 mg is likely to produce objective evi-dence of spinal anesthesia within 5 minutes.101,102 Askingthe patient whether or not she can wiggle her toes severalminutes after the test dose injection is not adequate. In onestudy, the presence of lower extremity warmth andimpaired pinprick response was only 93% sensitive forintrathecal injection, whereas impaired leg raise 4 minutesafter test dose injection had 100% sensitivity for intrathecalinjection.103

Finally, every anesthesia provider should remember thatno single test dose regimen can exclude every case of

unintentional intravenous or subarachnoid injection.104,105

Box 12-2 summarizes steps that may be taken to decreasethe risk of unintentional intravenous or subarachnoidinjection of local anesthetic.

Inadequate Anesthesia

Pain during anesthesia represents a higher proportion ofobstetric malpractice claims than of nonobstetricclaims.106 During labor, inadequate epidural analgesia mayresult from the inadequate extent of sensory blockade, non-uniform blockade, or inadequate density of blockade. Whencalled to evaluate breakthrough pain, the anesthesia pro-vider should first evaluate the extent of bilateral sensoryblockade in both the cephalad and caudad directions.Particularly if labor is progressing quickly, the extent ofsacral blockade may not be adequate. In this case, epiduralinjection of a large volume of local anesthetic may improvesacral blockade. In contrast, if the extent of sensory block-ade is adequate but the patient is still experiencing pain, the

TABLE 12-2 Test-Dose Regimens Designed to IdentifyUnintentional Intravascular Injection

Test Component* Response

Epinephrine 15 mg87 15- to 20-bpm increase inheart rate

Isoproterenol 5 mg96,97 15- to 20-bpm increase inheart rate

Local anesthetic alone: Tinnitus, circumoralnumbness, ‘‘dizziness’’Lidocaine 100 mg

Bupivacaine 25 mg2-Chloroprocaine

90 mgAir 1 mL98 Mill-wheel murmur over

right heart (use fetalDoppler probe to monitor)

Fentanyl 100 mg99,100 Dizziness, drowsiness

*Superscript numbers indicate references listed at the end of this

chapter.

BOX 12-2 Steps to Decrease Risk of UnintentionalIntravenous or Subarachnoid Injection of Local Anesthetic

� Lower the proximal end of the catheter below the siteof insertion. Observe for the passive return of bloodor cerebrospinal fluid.

� Aspirate before injecting each dose of local anesthetic.� Give the test dose between uterine contractions.� Use dilute solutions of local anesthetic during labor.� Do not inject more than 5 mL of local anesthetic as

a single bolus.� Maintain verbal contact with the patient.� If little or no block is produced after the injection of

an appropriate dose of local anesthetic, assume that thelocal anesthetic was injected intravenously, and removethe catheter.


density of blockade may be insufficient. In this case, theprovider should reestablish and maintain analgesia using amore concentrated solution of local anesthetic.

Total block failure usually results from failure to identifythe epidural space correctly or from malposition of thecatheter tip outside the epidural space (e.g., in a neurofora-men). A unilateral block may occur despite the use of goodtechnique. Unilateral block can often be prevented by limit-ing the length of catheter within the epidural space to 3 cmor less. The problem with limited insertion of the catheter isthat, in some patients, the catheter tends to migrate out-ward over time. (Patients undergoing surgery remain still;by contrast, laboring women change position frequently.)Obese women seem to be at higher risk for outward migra-tion of the catheter tip. Prospective studies suggest that 4 to6 cm is the optimal depth of epidural catheter insertion inlaboring women.60,61,107

Whether or not catheter withdrawal in the setting ofbreakthrough pain is beneficial is not clear. Beilin et al.108

compared catheter withdrawal followed by injection oflocal anesthetic with injection of local anesthetic withoutcatheter withdrawal for the treatment of breakthroughpain. The ability to rescue analgesia was not differentbetween the groups. Additionally, Gielen et al.109 per-formed a radiologic study in which they observed no con-sistent relationship between catheter position and theasymmetric onset of sympathetic blockade. Unilateral orpatchy sensory blockade likely results from the nonuni-form distribution of local anesthetic solution in the epi-dural space.110 Injection of a large volume of dilute localanesthetic solution into the epidural space usually correctsthis problem, regardless of the location of the tip of theepidural catheter (provided it is actually in the epiduralspace). If analgesia cannot be rescued with a second injec-tion, the catheter should be removed and replaced atanother interspace.

The management of inadequate anesthesia is more prob-lematic during cesarean delivery. Failure of spinal anesthe-sia may result from the maldistribution of local anestheticwithin the subarachnoid space.111,112 If inadequate spinalanesthesia is noted before incision, the anesthesia providermay perform a second spinal anesthetic procedure and giveadditional local anesthetic. However, in the ASA Closed-Claims Database, Drasner and Rigler112 identified threecases of cauda equina syndrome complicating spinal anes-thesia. In two cases, ‘‘failed spinal’’ anesthesia had occurred,followed by a repeat injection of local anesthetic. Theresearchers recommended that anesthesia providers deter-mine the presence of anesthesia in the sacral dermatomesbefore giving additional local anesthetic into the subarach-noid space. Additionally, they stated that if CSF was aspi-rated during the original procedure, it should be assumedthat local anesthetic was delivered into the subarachnoidspace, and the total dose of local anesthetic be limited tothe maximum dose a clinician would consider reasonable toadminister in a single injection.112 If partial blockade ispresent (even if it is limited to the sacral dermatomes),the second dose should be reduced accordingly. It mayalso be advisable to perform the second procedure at adifferent interspace or make other changes to the originalprocedure (e.g., alter the patient’s position, use a local anes-thetic with different baricity, or straighten the lumbosacralcurvature).

If the patient complains of pain after incision, the anes-thesia provider must decide between the administration ofinhalation or intravenous analgesia and the administrationof general anesthesia. Supplemental analgesia may be pro-vided by giving 60% nitrous oxide in oxygen, small incre-mental boluses of ketamine (0.1 to 0.25 mg/kg), or smallboluses of intravenous opioid. Supplemental infiltration ofthe wound with local anesthetic is sometimes helpful, espe-cially when spinal anesthesia regresses near the end of anunexpectedly long operation. The anesthesia provider mustensure that the patient remains sufficiently alert to protecther airway. In most cases, severe pain unrelieved by modestdoses of analgesic drug requires rapid-sequence inductionof general anesthesia, followed by endotracheal intubation.

In some cases, inadequate epidural anesthesia resultsfrom failure to give a sufficient dose of local anesthetic orfailure to wait a sufficient time after its administration.For example, after 0.5% bupivacaine is given epidurally,approximately 20 minutes must pass to achieve an adequatelevel of anesthesia, and additional local anesthetic may beneeded to achieve an adequate density of blockade. Inurgent cases or in cases with a ‘‘missed’’ segment, localinfiltration with a local anesthetic often results in satisfac-tory anesthesia. Sometimes it is difficult to separate thebeneficial effect of the local infiltration from the beneficialeffect of waiting for the obstetrician to obtain, prepare, andinject the local anesthetic solution. Finally, the anesthesiaprovider should exercise caution when initiating spinalanesthesia after failure of epidural anesthesia because of ahigher incidence of high spinal anesthesia in this setting.113

Presumably, the large volume of local anesthetic within, ornear, the epidural space results in decreased lumbar CSFvolume, which predisposes to high spinal anesthesia. It maybe advisable to reduce the dose of intrathecal local anes-thetic, particularly in the presence of partial epiduralblockade.

Equipment Problems

The frequency of major equipment malfunction is very lowduring the administration of neuraxial anesthesia. Mostanesthesia providers in the United States use disposableneedles, and the plastic needle hubs are attached to theneedles’ shafts with epoxy. Rarely, a needle breaks at thehub-shaft junction.114 If a needle should break, the portionof the needle that remains in the patient should beremoved, because it may migrate and cause injury.115

An epidural or spinal catheter may shear and break off ifthe catheter is withdrawn through a needle; thus an epidu-ral or spinal catheter should never be withdrawn in thismanner. Rather, if the catheter must be withdrawn, theneedle and catheter should be withdrawn as a unit. It isalso possible to break a catheter during attempts at remov-ing it, although this is rare. If resistance to catheter removalis encountered, the patient should assume a position thatreduces lumbar lordosis, thereby lessening the kinking ofthe catheter between perivertebral structures. If positionchange is not successful, the catheter should be tapedunder tension to the patient’s back and left undisturbedfor several hours. The catheter usually works its way outand is then easy to remove. Once the catheter has beenremoved successfully, it should be examined to ensurethat it has been removed completely. Complete removal


of the catheter should be documented in the medicalrecord.

Rarely, catheters do break on removal. We favor aggres-sive attempts to remove broken spinal catheters. However,it may be unnecessary to remove broken epidural catheters;rather, in these circumstances, the patient can be informedof the complication and observed over time. The incidenceof catheter migration or other delayed sequelae appears tobe low. Computed tomography may help identify theprecise location of a broken catheter, if necessary.116

During use, an epidural catheter occasionally becomesdisconnected from the catheter connector. Optionsinclude replacing the epidural catheter or reconnectingthe connector to the catheter. Langevin et al.117 used anin vitro model to investigate whether microbial contami-nation precludes reconnection. They found that an area ofthe interior of the catheter distal to the disconnection mayremain sterile for up to 8 hours if the fluid column withinthe catheter remains static (i.e., if ‘‘fluid does not movewithin the catheter when it is raised above the level of thepatient’’117). Therefore, they concluded that it may be safeto decontaminate the exterior of the catheter, cut thecatheter with a sterile instrument, and reconnect it to anew sterile connector. However, given the potential cata-strophic consequences of neuraxial infection, we recom-mend replacing the catheter. Also, wire-embeddedcatheters cannot be cut.

Resuscitation of the Obstetric Patient

Intravenous, spinal, or epidural injection of local anestheticmay rarely precipitate maternal cardiac arrest. If this eventoccurs before delivery, left uterine displacement must bemaintained and aortocaval compression avoided duringmaternal resuscitation. Initially, the ABCs of resuscitationare important; these include (1) the establishment andprotection of the patient’s airway, (2) the provision of ade-quate ventilation, and (3) the restoration and maintenanceof circulation.

The American Heart Association (AHA) has reviewedcardiopulmonary resuscitation in pregnant women.118 TheAHA guidelines state that standard algorithms and phar-macologic therapy should be used without modification forpregnancy. Left uterine displacement should be maintainedduring the resuscitation. If initial resuscitative efforts areunsuccessful, the obstetrician should consider emergencyhysterotomy (cesarean delivery), because it may be impos-sible to resuscitate the mother until adequate venous returnis restored. The decision to proceed with delivery dependson several factors, including gestational age, features of thecardiac arrest (e.g., duration of arrest and hypoxemia), andthe professional setting (skills of surgeon, anesthesia provi-der, neonatologist, and presence of support personnel). Ifgestational age is less than 20 weeks, a hysterotomy may beperformed to facilitate maternal resuscitation, but the fetuswill not be viable. After 24 weeks’ gestation, chances ofsurvival for both the mother and baby may be improvedwith delivery. The resuscitation team leader should con-sider emergency delivery as soon as the arrest occurs,because best infant survival has been observed when deliv-ery occurs within 5 minutes of the maternal arrest.118

Hysterotomy should therefore begin within 4 minutes ofthe arrest.

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KEY POINTS

� Physiologic changes of pregnancy alter neuraxialanatomy; alterations include accentuation of lumbarlordosis, a ‘‘softer’’ ligamentum flavum, anddecreased space in the spinal canal due to vascularengorgement of epidural veins.

� Physiologic changes of pregnancy cause a morepronounced response to neuraxial anesthesia–induced sympathetic blockade than is seen innonpregnant patients. These include higher baselinesympathetic tone and aortocaval compression.

� Pregnant women, particularly those with neuraxialblockade, should not be cared for in the supineposition but rather in lateral tilt or in the full lateralposition.

� Correct patient positioning, equipment, andtechnique are important to the success and safetyof neuraxial techniques.

� The midline approach is faster and less painful thanthe paramedian approach to the epidural orsubarachnoid space. However, the paramedianapproach may allow for the successful identificationof the subarachnoid or epidural space in difficultcases.

� Use of a non-cutting (‘‘pencil-point’’) needlefor spinal anesthesia reduces the incidence ofpost–dural puncture headache.

� Combined spinal-epidural (CSE) anesthesia has theadvantages of both spinal anesthesia and epiduralanesthesia.

� Approximately 20% to 30% less local anesthetic isrequired for epidural and spinal anesthesia inpregnant patients than in nonpregnant patients.

� Multiple techniques (e.g., test dose, aspiration,incremental dose injection) should be used to reducethe incidence and risk of unintentional subarachnoidor intravascular injection, because no one techniquewill completely exclude all cases of malpositionedneedles or catheters.

� During maternal cardiac arrest, resuscitation followsnormal guidelines but must be performed with thepatient in a left lateral tilt position. Earlyconsideration should be given to emergencyhysterotomy and evacuation of the uterus.


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