Local Anesthetic Techniques

Prepared by Dr. Mahmoud Abdel-Khalek

Jan 2015

Local Anesthetic Techniques

Local Anesthetic Drugs Regional Anesthesia

– Spinal Anesthesia– Epidural Anesthesia– Brachial Plexus Block– Bier’s Block

Local Anesthetic Drugs

Definition and Mode of Action LA are drugs that block the generation and

propagation of impulses in excitable tissues: nerves, skeletal muscle, cardiac muscle, brain

LA substances bind to a Na+ channel receptor on the cytosolic side of the Na+ channel (i.e. must be lipid soluble), inhibiting Na+ flux and thus blocking impulse conduction

LA must convert to an ionized form to properly bind to receptor

Different types of nerve fibres undergo blockade at different rates

Mechanism of Action Un-ionized local anesthetic diffuses into nerve axon

& the ionized form binds the receptors of the Na channel in the inactivated state

Local AnestheticsEsters

◦Procaine◦Chloroprocaine◦Tetratcaine◦Cocaine

Metabolism◦Hydrolysis by

pseudo- cholinesterase enzyme

Amides◦Lidocaine◦Mepivacaine◦Bupivacaine◦Etidocaine◦Prilocaine◦Ropivacaine

Metabolism◦Liver

Local Anesthetics & Baracity

Hyperbaric– Typically prepared by mixing local with

dextrose– Flow is to most dependent area due to gravity

Hypobaric– Prepared by mixing local with sterile water– Flow is to highest part of CSF column

Isobaric– Neutral flow that can be manipulated by

positioning– Very predictable spread– Increased dose has more effect on duration

than dermatomal spread

Absorption, Distribution, Metabolism

LA readily crosses the blood-brain barrier (BBB) once absorbed into the blood stream

Ester-type LA (procaine, tetracaine) broken down by plasma and hepatic esterases; metabolites excreted via kidneys

Amide-type LA (lidocaine, bupivicaine) broken down by hepatic mixed function oxidases (P450 system); metabolites excreted via kidney

Choice of LA depends on Onset of action –influenced by pKa (lower the

pKa, the higher the concentration of the base form of the LA and the faster the onset of action)

Duration of desired effects – influenced by protein binding (long duration of action when the protein binding of LA is strong)

Potency – influenced by lipid solubility (agents with high lipid solubility will penetrate the nerve membrane more easily)

Unique needs (e.g. sensory blockade with relative preservation of motor function, for pain management)

Potential for toxicity

Always be aware of the maximum dose for the particular LA used

Maximum dose usually expressed as (mg of LA) per (kg of body weight) and as a total maximal dose (adjusted for young/elderly/ill)

lidocaine maximum dose: 5 mg/kg (with epinephrine: 7mg/kg)

chlorprocaine maximum dose: 11 mg/kg (with epinephrine: 14 mg/kg)

Bupivacaine maximum dose: 2.5 mg/kg (with epinephrine: 3 mg/kg)

Maximum Dose of LA

Systemic Toxicity Occurs by accidental intravascular injection, LA

overdose, or unexpectedly rapid absorption Systemic toxicity manifests itself mainly at CNS and

CVS CNS effects first appear to be excitatory due to

initial block of inhibitory fibres; subsequently, block of excitatory fibres

CNS effects (in approximate order of appearance): Numbness of tongue Perioral tingling Disorientation Drowsiness Tinnitus Visual disturbances Muscle twitching Tremors

Convulsions Seizures Generalized CNS

depression Coma respiratory arrest

Systemic Toxicity

Treatment of LA systemic toxicity

Use the A, B, C’s for the management of local anesthetic toxicity

A= airway Maintain a patent airway, administer 100% oxygen

B= breathing May need to be assisted with positive pressure ventilation or intubation

C= circulation Check for a pulse If no pulse, initiate CPR

Seizures Diazepam in doses of 5 mg, or alternatively sodium pentothal in doses of 50-200 mg will decrease or terminate seizures

Treatment of LA systemic toxicity

Hypotension: – Rapid infusion of IV fluids– Place the patient in a head down position

(Trendelenburg)– Phenylephrine shots or infusion– Ephedrine (typically 5 mg shots)– If refractory treat the patient with epinephrine (5-

10 mcg shots) – Repeat and escalate the dose as necessary

The use of lipids in the treatment of local anesthetic toxicity has shown promise There are currently no established methods and research continues

Neuraxial Blocks

Anatomy The vertebrae are 33

number, divided by structural into five region: cervical 8, thoracic 12, lumber5, sacral 5, coccygeal3

Anatomy The vertebrae

are joined together by strong anterior and posterior longitudinal ligaments

Anatomy The spinal cord lies within the spinal canal

surrounded by meninges; Dura mater, subarachnoid space, then pia matter, end by Cauda equina (Hoarse tail)

The spinal cord receives blood supply from anterior and posterior spinal arteries

Spinal cord extends to L2, Dural sac to S2 Nerve roots (Cauda equina) from L2 to S2 Needle inserted below L2 should not

encounter cord, thus L3-L4 and L4-L5 interspace are commonly used for spinal anesthesia

Spinal Meninges

Dura Mater◦Outer most layer◦Fibrous

Arachnoid◦Middle layer◦Non-vascular

Sub Arachnoid Space◦Lies between the

arachnoid and piaPia

◦Inner most layer◦Highly vascular

Indications of Spinal/ Epidural Full stomach Anatomic distortions of upper airway TURP surgery Obstetrical surgery (T4 Level for CS) To relieve post-operative pain

Absolute Contraindications to Spinal/ Epidural Anesthesia

Lack of proper equipment or properly trained personnel

Patient refusal Lack of IV access Allergy to LA Infection at puncture site or underlying

tissues Uncorrected hypovolemia Coagulation abnormalities Raised ICP

Relative Contraindications to Spinal/ Epidural Anesthesia

Bacteremia Preexisting neurological disease Aortic/mitral valve stenosis Previous spinal surgery Back problems Severe/unstable psychiatric disease

or emotional instability (Uncooperative)

Spinal Anesthesia Technique

Preparation & Monitoring◦EKG◦NBP◦Pulse Oximeter

Patient Positioning◦Lateral decubitus◦Sitting◦Prone (hypobaric

technique)

Spinal Anesthesia Technique Midline Approach

– Skin– Subcutaneous tissue– Supraspinous ligament– Interspinous ligament– Ligamentum flavum– Epidural space– Dura mater– Arachnoid mater

Paramedian or Lateral Approach– Same as midline excluding

supraspinous & interspinous ligaments

Spinal Anesthesia Levels

Spinal Injection Sympathetic block is 2-6 dermatomes higher than sensory block Motor block is 2 dermatomes lower than sensory block

Complications of Spinal Anesthesia

Failed block Backache Hypotension, bradycardia if block reaches

T2-T4 (sympathetic nervous system block) Post-spinal headache

More common in women ages 13-40 Larger needle size increase severity (use

G23 or smaller) Onset typically occurs first or second day

post-op Treatment: Bed rest, Fluids, Caffeine, Blood

patch

Complications of Spinal Anesthesia

Extensive spread of anesthetic ("high spinal")

Persistent paresthesia (usually transient) Epidural or subarachnoid hematoma Spinal cord trauma Infection

Complications of Spinal Anesthesia Failed block Back pain (most common) Spinal headache

– More common in women ages 13-40– Larger needle size increase severity– Onset typically occurs first or second day

post-op– Treatment:

Bed rest Fluids Caffeine Blood patch

Blood Patch Effective treatment for postspinal

headache Increase pressure of CSF by placing blood

in epidural space If more than one puncture site, use lowest

site due to rostral spread May be done more than one time 95% success with first patch Second patch may be done 24 hours after

first

Epidural Anesthesia Larger dose of LA used

(12- 20 mL) LA deposited in epidural

space (potential space between ligamentum flavum and dura)

Widest at Level L2 (5-6mm)& Narrowest at Level C5 (1-15mm)

Safest point of entry is midline lumbar

Epidural Anesthesia Solutions injected

spread in all directions of the potential space; SG of solution does not affect spread

Initial blockade is at the spinal roots followed by some degree of spinal cord anesthesia as LA diffuses into the subarachnoid space through the dura

Epidural Anesthesia

Test Dose: 1.5% Lidocaine with Epinephrine 1:200,000◦Tachycardia (increase >30bpm over resting HR)◦High blood pressure ◦Light headedness◦Metallic taste in mouth◦Ring in ears◦Facial numbness◦Note: if beta blocked will only see increase in BP

not HRBolus Dose: Preferred Local of Choice

◦10 mL for labor pain◦20-30 mL for C-section

Epidural Anesthesia

Distances from Skin to Epidural Space– Average adult: 4-6cm– Obese adult: up to 8cm– Thin adult: 3cm

Assessment of Sensory Blockade– Alcohol swab

Most sensitive initial indicator to assess loss of temperature

– Pin prick Most accurate assessment of overall sensory

block

Complications of Epidural Anesthesia

Inadvertent dural puncture Inadvertent IV administration Hypotension (nausea & vomiting) Headache Backache Infection

Caudal Epidural Anesthesia Anatomy

– Sacrum Triangular bone 5 fused sacral

vertebrae Needle Insertion

– Sacrococcygeal membrane

– No subcutaneous bulge at site of injection after 2-3ml

Caudal Epidural Anesthesia

Dosages– S5-L2: 15-20ml– S5-T10: 25ml

Post Operative Problems– Pain at injection site is most common– Slight risk of neurological complications– Risk of infection

Brachial Plexus Block

Musculocutaneous Nerve

Median Nerve Ulnar Nerve Radial Nerve

Axillary approach of BPB

Advantages– Provides anesthesia for forearm & wrist– Fewer complications than a supraclavicular

block Limitations

– Not for shoulder or upper arm surgery– Musculocutaneous nerve lies outside of the

sheath and must be blocked separately Complications

– Intravascular injection– Elevated bleeding time increases risk for

hematoma

Axillary Approach Position

– Head turned away from arm being blocked

– Abduct to 90º– Forearm is flexed to

90º– Palpate axillary

artery for pulse The needle is

inserted adjacent to the artery

Axillary Block Dosing

– Lidocaine 1% 30-40ml

– Etidocaine 1% 30-40ml

– Bupivacaine 0.5%30-40ml

Note 40mL is most common vollume

Local Intravenous Anesthesia(Bier’s Block)

Suitable for upper limb below elbow& lower limb below knee surgeries

Advantages: Easy to administer, rapid onset, muscle relaxation and rapid recovery

Limitation Time! Ideal for procedures lasting 40-60 minutes Maximum time limit is 90 minutes Tourniquet pain generally starts after 20-30

minutes

Contraindications

Raynaud’s disease Sickle cell disease Crush injuries Young Children Must have a reliable/operative

tourniquet! If this can not be guaranteed then this technique should not be used due to risk of toxicity!

Mechanism of Action

Not clearly understood Local anesthetics, ischemia,

asphyxia, hypothermia, and acidosis all may play a role

Equipment

Operative and reliable double tourniquet Running IV in non-operative arm Resuscitation equipment Eschmarch bandage

Local Anesthetic Choice 0.5% lidocaine or 0.5% prilocaine Max dose is 3 mg/kg for either NEVER USE EPINEPHRINE CONTAINING

SOLUTIONS Complication of prilocaine is methemoglobinemia

in doses of > 10 mg/kg Treat with 1-2 mg/kg of 1% methylene blue given

over 5 minutes

Technique IV catheter in operative arm as distally

as possible

Technique IV catheter in operative arm as distally as

possible Double tourniquet on the operative arm

Proximal Cuff

Distal Cuff

Technique Have patient hold

arm up Use Eschmark

bandage to exsanguinate the arm

Exsanguinate the arm from distal to proximal

Inflate the proximal tourniquet to 150 mmHg over the patients systolic pressure

Proximal Cuff

Distal Cuff

Confirm the absence of a radial pulse

Inject your local (0.5% lidocaine or prilocaine in a dose of 3 mg/kg)

Remove IV catheter, hold pressure and have OR staff prepare arm Onset of anesthesia should occur in 5 minutes

When the patient complains of pain you can inflate the distal tourniquet and then deflate the proximal

tourniquet

Proximal Cuff

Distal Cuff 1st

2nd

Minimum time for tourniquet inflation

The tourniquet should be up for at least 25 minutes…releasing it before this may result in toxicity

Releasing the tourniquet in cyclic deflations (10 second intervals) will decrease peak levels of local anesthetic

Complications

Tourniquet discomfort Rapid return of sensation after

tourniquet release and subsequent surgical pain

Toxic reactions from malfunctioning tourniquets or deflating the tourniquet prior to the 25 minute limit

Thank You