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
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Mechanism of Action
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Un-ionized local anesthetic diffuses into nerve axon & the
ionized form binds the receptors of the Na channel in the
inactivated state
Local Anesthetics
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Esters
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Procaine
Chloroprocaine
Tetratcaine
Cocaine
Metabolism
◦ Hydrolysis by pseudocholinesterase enzyme
Amides
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Lidocaine
Mepivacaine
Bupivacaine
Etidocaine
Prilocaine
Ropivacaine
Metabolism
◦ Liver
Local Anesthetics & Baracity
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Hyperbaric
– Typically prepared by mixing local with dextrose
– Flow is to most dependent area due to gravity
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Hypobaric
– Prepared by mixing local with sterile water
– Flow is to highest part of CSF column
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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
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Maximum Dose of LA
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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)
Systemic Toxicity
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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):
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Numbness of tongue
Perioral tingling
Disorientation
Drowsiness
Tinnitus
Visual disturbances
Muscle twitching
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Tremors
Convulsions
Seizures
Generalized CNS
depression
Coma
respiratory arrest
Systemic Toxicity
Treatment of LA systemic
toxicity
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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
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Neuraxial Blocks
Anatomy
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The vertebrae are 33
number, divided by
structural into five
region: cervical 8,
thoracic 12, lumber5,
sacral 5, coccygeal3
Anatomy
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The vertebrae are
joined together by
strong anterior and
posterior
longitudinal
ligaments
Anatomy
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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
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Dura Mater
◦ Outer most layer
◦ Fibrous
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Arachnoid
◦ Middle layer
◦ Non-vascular
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Sub Arachnoid Space
◦ Lies between the arachnoid
and pia
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Pia
◦ Inner most layer
◦ Highly vascular
CSF
Indications of Spinal/ Epidural
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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
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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)
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Spinal Anesthesia Technique
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Preparation & Monitoring
◦ EKG
◦ NBP
◦ Pulse Oximeter
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Patient Positioning
◦ Lateral decubitus
◦ Sitting
◦ Prone (hypobaric
technique)
Spinal Anesthesia Technique
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Midline Approach
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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
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Spinal Injection
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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
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 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
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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
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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
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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 (1220 mL)
 LA deposited in epidural
space (potential space
between ligamentum
flavum and dura)
 Widest at Level L2 (56mm)& Narrowest at Level
C5 (1-1.5mm)
 Safest point of entry is
midline lumbar
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Epidural Anesthesia
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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
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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
HR
Bolus Dose: Preferred Local of Choice
◦ 10 mL for labor pain
◦ 20-30 mL for C-section
Epidural Anesthesia
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Distances from Skin to Epidural Space
– Average adult: 4-6cm
– Obese adult: up to 8cm
– Thin adult: 3cm
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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
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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
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Caudal Epidural Anesthesia
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Dosages
– S5-L2: 15-20ml
– S5-T10: 25ml
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Post Operative Problems
– Pain at injection site is most common
– Slight risk of neurological complications
– Risk of infection
Brachial Plexus Block
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Musculocutaneous
Nerve
Median Nerve
Ulnar Nerve
Radial Nerve
Axillary approach of BPB
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Advantages
– Provides anesthesia for forearm & wrist
– Fewer complications than a supraclavicular block
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Limitations
– Not for shoulder or upper arm surgery
– Musculocutaneous nerve lies outside of the sheath
and must be blocked separately
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Complications
– Intravascular injection
– Elevated bleeding time increases risk for hematoma
Axillary Approach
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Position
– Head turned away from
arm being blocked
– Abduct to 90º
– Forearm is flexed to 90º
– Palpate axillary artery
for pulse
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The needle is inserted
adjacent to the artery
Axillary Block
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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
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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!
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Mechanism of Action
Not clearly understood
 Local anesthetics, ischemia, asphyxia,
hypothermia, and acidosis all may play a
role
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Equipment
Operative and reliable double tourniquet
 Running IV in non-operative arm
 Resuscitation equipment
 Eschmarch bandage
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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
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Technique
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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
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Proximal Cuff
Distal Cuff
Technique
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Have patient hold arm
up
Use Eschmark bandage
to exsanguinate the arm
Exsanguinate the arm
from distal to proximal
Inflate the proximal tourniquet to 100 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
2n Proximal Cuff
d
1s Distal Cuff
t
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
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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
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Thank You