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PERIPHERAL NERVE BLOCKS

DR.MU

SHTAQ

AHMA

D

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INTRODUCTION

Local anesthetic induced blockade of peripheral nerve impulses from a targeted body part with preserved level of consciousnessInjecting local anesthetic near the course of a named nerve •Surgical procedures in the distribution of the blocked nerve

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STRUCTURE OF NERVE4

CLASSIFICATION

Regional anaesthesiaCentral neuraxial blocks

Subarachnoid

epidural

Peripheral blocksTruncal

Plexus

Distal

Field & topicall

IV regional anaesthesia

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ADVANTAGES

Avoids general anaesthesia complications

• Safer than GA especially when anaesthetist is inexperienced

Pt remains awake .....pt will & helpfull for suegeon----feedback

Postops analgesia----continue / catheter

Less PONV-----less opiods need

Less post ops sedation------less confision(cognitive functions) in elderly

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Faster return to street fitness & early discharge

Cheep & relatively safe in remote location

hemodynamic stability than neuraxial & GA

Sole anesthetic technique , supplemented with monitored anesthesia care (moderate sedation) or with a "light" general anesthetic

Preemptive analgesia

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Less immunosuppressive than GA

• Hemodynamically compromised• Too ill to tolerate GA• MH• PONV is risk

Excellent alternative to GA

• Modern equipments—USG,Nerve stimulator ect

Growing popularity of RA & PNB

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DISADVANTAGES

TIME DELAY

• 15-30 MIN –Procedure & onset

PATIENT FACTORS

• Discomfort due to procedure & positioning & awake during surgery• Distress due to paralysis & numbness---postops• Managed easily—benzodiazepine & opiods

SURGEON FACTORS

• Irritated by awake & conversation with surgeon

ANAESTHETIST FACTORS

• Skill, knowledge & proper equipments

BLOCK FAILURE

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NERVE DEMAGE

• Chronic paresthesias• Permanent N damage

FAILURE RATE-----10%

• If No catheter----GA

SURGERY OUTLASTS THE BLOCK

• Respiratory failure-phrenic N Block• Seizures ---intra-arterial injection

LOCAL ANAESTHETIC TOXICITY

SPECIFIC COMLPICATIONS RELATED TO NERVE BEING BLOCKED

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CONTRAINDICATIONS OF PNB

COTRAINDICATIONS

ABSOLUTE RELATIVE

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ABSOLUTE COTRAINDICATI

ONS Patient refusal• Hemophilia• DIC• Anticoagulant drugs

Inexperienced ,incompetent anaesthetist

Major coagulation disorders & drugs

Infection at site

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Related to specific N Block

• Interscalene block• with contra lateral phrenic N paralysis• Severe pulmonary disease

Increased risk of LA toxicity

• Bilateral axillary Block• Multiple intercostal blocks

LA Allergy-anaphylaxis

• Penile block,toes,fingers etc

Ring block at site---end arteries---LA containing Adrenaline

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RELATIVE COTRAINDICATI

ONSDemented , combative & uncooperative patients

Pediatric patients

Placing block under GA

Surgeons who feel uncomfortable

Uncertain duration of surgery

Bloodstream infection

Preexisting peripheral neuropathy

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COMPLICATIONS

Local anaesthetic toxicity

Nerve damage

Vasoconstrictor problems

Infection

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Haematoma• Bleeding disorder• Anticoagulant drugs

Wrong drug• supra &infra clavicular• inter costal block

Pneumothorax• Vasovagal –mistaken as LA toxicity• Anxious pt--sedate

Psychological reaction

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1.LA TOXICITY

Immediate or delayed-----signs & symptoms (CNS & CVS)

• Maintain IV line before• Have resuscitation equipments & drugs• Always aspirate before injecting• Inject slowly & aspirate after every 3-5 ml• Stabilize needle ……short fine bore plastic tubing b/w needle & syringe (isolated needle technique)• Observe pulse,ECG & sign of IV injection

Prevention ---always

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UNIPOLAR INSULATED

NEEDLE19

2.NERVE DAMAGE

Direct by needle or by injection of LA

• Withdraw 1-2 mm after eliciting paraesthesia-before injection

Eliciting paraesthesia technique -----can damage

• 1 in 1000 blocks• Most dysaesthesiasis & paresis resolve—few months• 1 in 10000 blocks=permanent demage

Incidence---experienced anaesthetist

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RECOMMENDATIONS TO REDUCE RISK OF

NERVE DAMAGE

Use short B- bevel needle

• STOP –undo resistance & severe pain-----withdraw & then reinject

Use nerve stimulator & insulated short bevel needle

Avoid rapid,forceful injection

Avoid block under GA

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4.VASOCONSTRICTOR PROBLEM

General rule—epinephrine should not be used in concentration > 1:200000 (5ug/ml) in PNB

• Skin ----- 1:300000 or 1:400000 sufficient• Dentist –1:80000 but in small vol

Never use----areas of endarteries

Careful-----ischemic areas---varicose leg ulcer

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H/O IHD-----avoid/reduce dose---- can cause palpatation,angina,HTN• Adding sodium bicarbonate• Felypressin in stead of epinephrine• Warming the sol to body tempPregnancy-----epinephrine in significant quantity reduce placental circulation -----avoid /reduce dose

Max recommended dose of epinephrine--- 4 ug/kg

Epinephrine sol-----lower Ph--pain on injection-----can be reduced by

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INFECTION

Aseptic technique

• 1% chlorhexidine in 75% alcohol—allergic to iodine

No needle prick through infected skin except abscess

Use antiseptic Alcoholic Betadine(povidone/ iodine in ethanol)

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PREPARATION

FEW GOLDEN RULES

• Designed procedure room—block room• Insert an intravenous lin e before • Monitor (pulse oximetry,EG G , BP • Practice proper aseptic technique .• Resuscitation equipments at hand • Patients informed consent• Adequate knowledge of the correct

tehnique an d know how to handle complications

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PREMEDICATION

Anxiolysis with Benzodiazepines and/or opiods

Light sedation----elicitation of paraesthesia technique

Deep sedation----nerve stimulator

O2 supplementation----heavy sedation

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EQUIPMENTS

Nerve stimulator—ECG Electrode• different lengths ( 25- 150 mm)and (20 to 25G).• tip may angled at 15 or 30 degrees.• catheters

Unipolar insulated B-Bevel needles

Ultrasounds machine

Syringes

Local anaesthetic

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BLOCK ROOM28

EQUIPMENTS FOR PNB

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CurrentDuration

frequency

DIAL

ANODE

CATHODE

NERVE STIMULATOR

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Cathode-connectected with needle

Anode to patientThrough ECG

electrode

IDEAL ELECTRICAL CHARACTERISTICS OF A

PNS

Constant current (DC)generator • circuit disconnection alert, • impedence alerts, • low battery and • malfunction alert

Monophasic rectangular output pulse i.e. the current flows in one direction only.

Ability to vary pulse duration (0.1 - 1ms)

Digital display of actual flowing current

Safety features like

Leads should be clearly marked to avoid confusion as to which is cathode and anode

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NERVE STIMULATOR

Current range from 0.1-6.0 mA

• Linear & constant• Low output

Pulse Frequency

• 1 Hz -Mixed nerve• 2 Hz - Sensory nerve

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SETTINGS OF PNS

Desired initial---USUALLY

• current (1 - 2mA),• pulse duration (0.1ms) and • frequency (2hz).

A threshold current of less than 0.5ma usually results in a successful block

current less than 0.2ma, increased resistance on injection or pain on injection may suggest intraneural needle placement

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WHY PATIENT DOES NOT FEEL PAIN DURING PNS?

Chronaxie is the length of time the current must be applied to the nerve to initiate an impulse

F aster conducting nerves like the A α motor nerve fibres have a smal ler chronaxie due to a shorter refractory period than the slower conducting sensory nerves like Aδ or the unmyelinated C sensory nerve fibres.

possible to stimulate a motor nerve but not the sensory nerve by using a current of smaller chronaxie (shorter time) . Th is means a motor response can be seen without producing pain-----however patient still feels TINGLING.

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CHRONAXIE OF DIFFER ENT NERVES

NERVE FEATURE CHRONAXIE-ms

C Unmyelinated 0.40

Aδ myelinated 0.17

Aα myelinated 0.05 - 0.10

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WHAT IS HZ ?

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Cycles/second

STIMULATION AND INJECTION

TECNIQUEInitial current

2-3 mAFrequency

1-2 Hz

Threshold current 0.3- 0.5 mA

Aspirate– inj LA 1-2 ml----no pain &

resistance

Aspiration test 5- 10 ml LA injected

slowly

Increase the current to initial

level

No stimulatory response -inject the remaining

drug

Recurring response - May

indicate intraneural needle

position

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USING NERVE STIMULATOR

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UNIPOLAR B-BEVEL NEEDLES

less-experienced practitioners, the shortest recommended needle is generally safest

longer needle (up to 5 cm) may also be indicated in morbidly obese or very muscular patients.

approach and the patient population--e.g., adult vs. pediatric,

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25-150 mm20-25G

INSULATED B-BEVEL NEEDLE

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TOUHY SET FOR CATHETERIZATION

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TOUHAY SET FOR PERIPHERAL NERVE CATHETERIZATION

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Stimulating catheter

CURRENT ADJUSTABLE INSULATED NEEDLE SET

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CONTINUOUS PNB SYSTEM

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ELASTOMERIC BALOON PUMP

MEDIAN NERVE CATHETER

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postoperative pain relief after hand surgery. Continuous infusion of levo-bupivacaine 0,125% - 2-5 ml/h

ULTRASOUND MACHINE

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LAPTOP U

LTRASOU

ND

MACH

INE

Direct visualization of nerves & other structures

Visualization of LA spread

Re-position of needle in case of misdistribution of LA

Avoidance of side effect- due to excess dose of LA

ADVANTAGES OF USG

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Avoidance of painful muscle contractions due to PNS

Faster onset

Longer duration of blocks

Improved quality

Blocks under GA

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Short Axis (SAX) –

• probe is aligned perpendicular to the axis of the nerve, the nerve is seen in cross section

Long Axis (LAX) –

• probe is aligned parallel to the axis of the nerve

Short Axis View is preferred due to easy identification of nerves, more stable view & allows to visualize circumferential spread of LA------ “Doughnut” sign

BASIC VIEWS ON USG53

Ultrasound scanned image obtained in the infragluteal fossa midway between the greater trochanter and ischial tuberosity with the probe oriented along the long axis of the sciatic nerve. The sciatic nerve is

seen as a long tubular structure located deep to the muscles

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Ultrasound scanned image of the femoral nerve surrounded byHypoechoic (dark) local anesthetic (L) creating a “doughnut” sign

Doughnutsign

In plane (IP) – long axis of the needle is oriented to the long axis of the probe

• Entire needle can be seen

Out of plane (OP) – the long axis of the needle is the oriented perpendicular to long axis of the probe

• Only part of the needle is seen

NEEDLE APPROACHES

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Schematic representation of the views and needle approaches for nerve blocks with ultrasound imaging. A. Short axis view of a nerve with an out-of-plane needle approach. B. Short axis view of a nerve with an in-plane needle approach. C. Long axis view of a nerve with an out-of-plane needle approach. D. Long axis view of a nerve with

an in-plane needle approach. Modified6.

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Picture showing the orientation of the ultrasound probe and the needle for placement of an interscalene block with

the in-plane needle approach

VIEW SHORT /LONG ?

TECHNIQUES

Single injection

• Intermittent dose• Continuous

Multiple injections---axillary block

• Large vol of LA in general location of cutaneous N• Minor/superficial surgery• Supplement to PNB & Neuraxial blocks

Using catheters

Field block---superficial cervical plexus block

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FEMORAL NERVE CATHETERIZATION

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CHOICE OF LOCAL

ANAESTHETICSPurpose of block

• Anaesthesia or analgesia

Onset

Duration of block

Site & area of block—vol

Degree of sensory Vs motor block

Maximum toxic dose

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LA USED FOR PNB64

CONCENTRATION

ANAESTHESTHETIC BLOCK

• 1.5-2% Plain Lignocaine----------max 3 mg / kg • 1.5-2% Lignocaine with adrenaline--- 7mg / kg • 0.5% Bupivacaine---------max 2 mg / kg• Mepivacaine 2%• o.75 % Ropivacaine-------max 2-3 mg / kg

ANALGESIC BLOCK

• 0.125% Bupivacaine, 0.2% Ropivacaine, • Opiods, Clonidine.

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PNB PLACEMENT TECHNIQUES

Anatomy

Evoked paraesthesia

Nerve stimulator (goal 0.2-0.5 mA)

Ultrasound guided

Percutaneous electrical guidance

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OTHERS1.Droppler2.CT3.MRI

LA-- in Perineural

area

CONCLUSION

Not as a first case

Centralize your equipment

Select proper block

Good knowledge of anatomy

Know about potential complications on treatment

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Select right patient

Pick the right surgeon

Be confident about your block

But still if you fail--Failures are the stepping stones for success

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QUESTION 1

Anaesthetist was performing a peripheral nerve block with help of nerve stimulator & ultrasound ……he introduces insulated short bevel 22G needle at location…….& observe muscle contractions in nerve related area at 0.3 mA(n=0.2-o.5 mA).after injecting 1ml of LA muscle cotractions disappear.He injects rest of 10ml sol in incremental doses.Surgeon strat surgery after5 minutes but Pt feels pain……..Anaesthetist is quite sure about block……WHY Pt. feels pain ??

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QUESTION 2

Anaesthetist introduced insulated long bevel needle to block a peripheral nerve & observes muscle contractions at 0.2 mA ……….while he injected 1ml of LA ,……he had to stop the injection due to severe pain………moreover muscle contraction did not disappeared ..

• WHY SEVERE PAIN ON INJECTION…?• WHY MUSCLE CONTRACTIONS DID NOT DISAPPEAR ON INJECTING

LA….?• WHAT SHOULD BE THE ACTION OF ANAESTHETIST NOW…?

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THANKS

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