Central Neuroaxial Blockade

Dr Sachin Gaikwad

Applied Anatomy

Vertebral column consist of 33 vertebra

7 cervical , 12 thoracic , 5 lumbar , 5 fused sacral and 4 fused coccygeal vertebra.

Vertebral column curves

4 curvesKypotic curves- Thoracic and sacral

Lordotic curves-lumbar and cervical

Vertebral canal boundaries

Surface landmarks

Epidural Space ( Extradural or Peridural space)

It lies outside duramater.

Extends from foramen magnum to sacral hiatus.

It is triangular in shape with apex dorsomedial

Contents of epidural space

Anterior and posterior nerve root

Epidural veins

Spinal arteries

Lymphatics

Fat

Epidural Veins

Venous plexus of Batson

Valveless veins connecting pelvic veins to cranial veins directly

Accidental injection of air or LA can directly ascend to cranium

These veins directly drains into IVC so whenever there is obstruction to vena caval flow as in pregnancy ,abdominal tumours these veins are engorged reducing the size of epidural space and less dose is required.

Anatomy of Spinal Cord

Extend from medulla oblongata to lower border of L1 in adults.

In infants and neonates it ends at the lower border of L3

Adult level is achieved by 2 yr of age

So in infancy spinal anaesthesia is given at L4-L5 space.

Below L1 vertebral canal is occupied by lumbar,sacral and coccygeal nerve roots in oblique and downward direction forming cauda equina (horse tail).

Divides into 31 pairs of spinal nerves

8 cervical ,12 thoracic,5 lumbar,5 sacral and 1 coccygeal.

Each spinal nerve has anterior and posterior root.

Important dermatological segment levels

T4 Nipples

T6 - Xiphisternum

T10 Umbilicus

L1- Inguinal ligament

S1 to S4 - Perineum

Segmental levels of Spinal reflexes

T7,8 Epigastric

T9-T12- Abdominal

L1,2- cremasteric

L2,3,4- Knee jerk

S1,2 Ankle jerk

S4,5- Anal sphincter

S1,2- Planter

Meninges

Inside to outside by piamater ,arachnoid and duramater.

Duramater extends up to S2 in adults and up to S4 in infants while piamater extends as filum terminale up to coccyx.

Cerebrospinal Fluid

CSF is present between pia and arachnoid mater ie subarachnoid space that is why spinal anaesthesia is also called as subarachnoid block.

Secreted by choroid plexus of 3rd , 4th and lateral ventricles and is absorbed into venous sinuses via arachnoid villi

500 ml in 24 hours.

Volume of CSF at one time is 140ml , half of which is present in cramium and half in spinal canal.

Sp.gravity = 1.003 to 1.009 ( avg 1.004)

.pH 7.35

CSF pressure 100- 150 mm of H2O

Advantage over GA

Cheap

Less risk of pulmonary aspiration

Respiratory complications are obviated like bronco-spasm,post op atelectasis

Systemic effect of GA drugs not seen

Consequences failed intubation avoided

Disturbances of body chemistry are avoided

Bleeding is less because of low mean arterial pressure

Decreased incidence of thromboembolism due to increased vascularity of lower limbs.

Physiological alteration of central Neuroaxial blocks

Cardiovascular SystemMost prominent effect is hypo tension

Venodilation because of sympathetic block

Dilatation of post arteriolar capillaries

Decreased cardiac output

Decreased venous return

Bradycardia

Decreased catecholamine release due paralysis of nerve supply of adrenal glands

Supine hypotension syndrome- compression of IVC and aorta by pregnant uterus,abdominal tumours.

Bradycardia is due toBainbridge reflex decreased arterial pressure because of decreased venous return.

Direct inhibition of cardioacceletor fibres T1 to T4.

Nervous system

Sequence of blockage of nerve fibresAutonomic-> Sensory -> Motor

Recovery in reverse order

Autonomic level is 2 segment higher than sensory which is 2 segment higher than motorThis is called as differential blockage .

Autonomic level is tested by temp.,sensory by pin prick and motor by toe movement.

Respiratory system

Tidal volume , minute volume, arterial oxygen tension are well maintained

Apnea may occur due to severe hypotension causing medullary ischemia. Other causes are High spinal (C3,C4,C5),Total spinal,Accidental injection of LA in systemic circulation

Gastrointestinal system

Contracted gut with relaxed sphincters due to sympathetic block with parasympathetic over activity

Nausea

Vomiting

Liver no impairment

Excretory system and reproductive system

Renal function not impaired unless MAP falls below critical pressure of Kidney for auto-regulation ( 55 mm of Hg)

Urinary retention due blockage of sacral parasympathetic fibres (S2,3,4)

Engorgement of penis

Endocrine system

Stress response to surgery is inhibited

Hypoglycaemia due to augmented response to insulin

Increased in ADH is supressed during surgery

Thermoregulation

Vasodilatation causes hit loss which is compensated by vasoconstriction above the block and shivering

Spinal Anaesthesia

Subarachnoid block

Intrathecal block

Indications

Orthopaedic surgery of lower limb and pelvis

General surgery all pelvic and perineal surgeries , hernia,hydrocele, appendix,testicular surgeries.

Gynaecological and obs hysterectomy,myomectomy, C section, tubectomy,tuboplasty,ovarian surgeries,cervical surgeries

Urology- bladder and ureteric stone,prostate

Procedure

Position lateral ,sitting, prone

Approach mid-line, paramedian, lumbosacral (Taylor)

Under AAP spinal needle is inserted in Sub arachnoid space and after confirmation of free and clear flow CSF LA is injected.

LA mainly act on spinal nerves and dorsal ganglion.

In the horizontal supine position ,hyperbaric local anesthetic solutions injected at the height of the lumbar lordosis (circle) flow down the lumbar lordosis to pool in the sacrum and in the thoracic kyphosis. Pooling in the thoracic kyphosis is thought to explain the fact that hyperbaric solutions produce blocks with an average height of T4-6.

Drugs used for SA

Xylocain 5% made hyperbaric by addition of 7.5% dextrose.

Bupivacaine 0.5% made hyperbaric by addition of 8% dextrose.

Tetracaine - 1% made hyperbaric by addition of 5% dextrose.

Procaine - 10% made hyperbaric by addition of 5 % dextrose.

Opioid-

DrugConcentrationSpecific gravity

Lignocaine5% in 7.5% in D1.0333

Bupivacaineo.5% in 8% in D1.0273

Tetracaine1% in 5% in D1.0203

Procaine10 % in 5% in D1.0203

Spinal Needles

Dura cutting and dura separating

Dura cutting- Quincke- bobcock ,Greene

Dura separating these are pencil tip point end. Whitre ,sporte and pitkin

Incident of Post spinal puncture headache and cost

Factors affecting the height of the block

Volume of drug- greater volume higher level

Baricity it is the ration of sp. Gravity of an agent at body temperature to sp. Gravity of CSF at same temperature.

Hyperbaric technique- common ,outcome is govern by position of patient Hypobaric technique- less common,agent used is tetracaine 0.3% which is made hypobaric by addition of sterile water. Useful in colorectal surgery and applied in prone position where head is lower than buttocks ( Jack Knife position.Isobaric technique- commonly used bupivacaine 0.5% plain.settled at the same level of injection

Position of patient- very important factor eg if Trendelenburg position is given then same volume will produce a much higher block

Intra Abdominal pressure in ascities,pregnancy,abdo tumours decreases volume of subdural space and increases CSF pressure producing higher blocks

Spinal curvature- by affeccting contour of sub arachnoid space can affect the level of block

Patient factors Age -in old age due to reduced spinal and epidural space chances of higher block Obesity affects block due to increase in intra abdo pressureHeight- taller patient have long spine so require more drug and vice versa.

Factores affecting duration of block

Dose

Increased concentration of agent

Pharmacological profile of drug like protien binding ,metabolism

Type of drug used .Bupivacaine vs lignocaine

Addetives- Adrenaline,opiod.

Complications of SAB

1 Hypotension

Most common complication

Mild hypotenison do occure in all patients but in 1/3rd patient BP may fall < 90 systolic

Treatment-

Prophylactic- preloading with 1 to 1.5 L of crystalloid

Curative-

Head low position to increase venous return up to 15 %

Fluids- colloids are better than crystalloids

Vasopressors ephedrine,mephenteramine,methoxamine( sympatho memetic actin

I notropes- Dopamine ,dobutamine improve cardiac output

Oxygen inhalation prevent hypoxia of brain

2 Bradycardia

Treatment IV atropine

3. Respiratory paralysis

Apnea it usually because of hypotension so treat hypotension .if high or total spinal then give IPPV

Slight respiratory difficulty is treated with oxygenation and reassurance

4. Nausea and vomitting

Because of central hypoxia due to hypotension

Treatment treat hypotension,oxygenation, antiemetics

5. Difficulty in phonation

Due to high spinal block involving cervical level

Treatment IPPV

6.Restlessness,anxiety,apprehension

Ruleout hypoxia then reassure and sedate

7 LA toxicity

Due to intra vascular injection

Treat symptomatically

8.Cardiac arrest

May be due to total / High spinal,severe hypotension,LA toxicity/ anaphylaxis

Start CPCR

9 .High spinal /Total spinal

If involving lower inter costal then patient will complain of dysnea, give oxygenation and reassurance

If high to block cardioaccelerator fibres then sever bradycardia & hypotension

If too high to involve cervical fiber then IPPV may required

10. Miscellaneous

Pain during injection

Bloody tap

Broken needle

Post OP complications

Urinary retention due to blockage of S2,S3 S4 .Catheterisation may require

Post spinal headache-Post dural puncture headache

Meningitis- chemical ,infective

Cauda equina syndrome- due direct injury to nerve fibres by needle or LA agent. Mostly seen with continuous spinal with small bore catheter.

Paraplegia- epidural hematoma, abscess

Spinal cord ischemia -severe prolong hypotension, use of vasocontrictors

Local toxicity of LA like chloro procaine can injure spinal cord and can cause paraplegia

Anterior spinal artery syndrome- Epidural haematoma,abscess, epidermoid tumour can lead to compression of anterior spinal artery causing anterior spinal artery syndrome manifested by motor deficit without involving posterior column.

Contraindications

Absolute

Raised intra cranial pressure

Patient refusal

Severe hypo volumic shock

Patient on anti coagulant

Thrombolytic / fibrinolytic therapy

Bleeding disorders / coagulopathies

Septicemia and bacteremia

Infection at local site

Relative

Fixed cardiac output lesions( AS , MS)

Mild to moderate hypo volemia or hypotension

Uncontrolled hyper tension

H/o recent MI,severe ischemic heart disease

Heart blocks and patient on beta blockers

Patients on aspirin

Patients on low dose heparin

Spinal deformity

Previous spinal surgery

History of headache

GIT perforation

Neuropathies

CNS disorders

Spinal anaesthesia in children

Should be given in low space L4-L5

Preloading is not require as children less than 8 years are virtually free of heamodynamic side effects

Use of narcotics is contra indicated

Chances of systemic toxicity is high

EPIDURAL ANAESTHESIA

Indications

All surgeries under spinal block can be performed under epidural block.

Mainly used for controlling post op pain

Painless labour

To control chronic pain

To control pain due to cancer

Acute occlusive vascular conditions

Blood patch for post spinal headache

Epidural needle

Most common is Tuophys needle

It is blunt bevel with curve of 15 to 30 degree at tip.This curve is called as Huber Tip.

Weiss is winged

Crawford straight blunt bevel with no curve

Technique

Like in spinal it can be given in sitting or lateral.Usually epidural space is encountered 4 to 5 cm from skin and it has negative pressure .

Methods to locate epidural space

Loss of resistance technique after piercing ligamentum flavum there is loss of resistance.

Hanging drop technique ( Guttierrezs sign)- drop of saline in hub sucked in due to negative pressure .

MacIntosh extradural space indicator

Movement of bubble on Odoms indicator

Confirmation

Test dose of 1ml of hyperbaric lignocaine with adrenaline is given if in 5 min there is no evidence of either spinal block or intravascular injection further dose can be given

Then epidural catheter is passed through the needle and 3 to 4 cm of catheter should be in epidural space. Microfilter is attached to prevent contaminationOnset of action 15 to 20 min

Successful block is assessed by absence of knee jerk and pain by pin prick

Site of action of drug

Mainly Anterior and posterior nerve roots

Mixed spinal nerve

Drug diffuses through dura and arachnoid and inhibits descending pathways in spinal cord

Drugs used

NO Drugsconcentration

1Lignocaine1-2 %

2Bupivacaine0.25- 0.5 %

3Chloroprocaine2-3 %

4Mepivacaine1-2 %

5Prilocaine2-3 %

LA

OpioidsMorphine- 4 to 6 mg Fentanyl- 100 mcg ( diluted in 10ml NS) onset within 10 min last for 2 to 3 hours

Fentanyl + bupivacaine for post op analgesia and painless labour.

Advantage of opioid Only sensory block

Long lasting effect

No sympathetic block

Disadvantage

Respiratory depression

Urinary retention

Pruritus

Nausea and vomiting

Sedation

Factors affecting level

Volume of drug

Age

Gravity

Intra abdominal tumours, pregnancy

Speed of injection

Level of injection

Length of vertebral column

Conc of LA

Complications

Inadequate block

Hypotension

Apnea

Total Spinal

Dural puncture

Subdural block

Intravascular injection

LA toxicity

Horners syndrome

Epidural heamatoma

Epidural abscess

Anterior spinal artery syndrome

Direct injury to cord

Brocken catheter

Meningitis

Advantage of epidural anaesthesia

Less hypotension

No post spinal headache

Level of block can be changed

Any duration of surgery can be performed

Comparison

Spinal Epidural

1 costCheaper Expensive

2 onset of action Early Delayed

3 TechnicallyEasier Difficult

4 Duration of actionLess Prolonged

5 Quality of blockExcellent May be patchy

6 Change of level Not possible after fixationCan be possible

7 Block failure rateLessHigh

8 Post dural puncture headacheSeen Not seen

9 epidural HeamatomalessHigh incidence

10 Total spinalrareHigh

11 intravascular injrareHigh chance

12 drug toxicitylesshigh

13 Catheter complicationsNot seenpresent

Thank you