LOCAL ANESTHETICS
AND REGIONAL
ANESTHESIA
Dr Walid Zuabi
FCA RCSI
Local Anesthetics- History
◼ 1860 - cocaine isolated from erythroxylum coca.
◼ Koller - 1884 uses cocaine for topical anaesthesia.
◼ Halsted - 1885 performs peripheral nerve block with LA.
◼ Bier - 1899 first spinal anesthetic .
Local Anesthetics - Definition
A substance which reversibly inhibits nerve conduction when applied directly to tissues at non-toxic concentrations.
◼ Local anesthetics block generation, propagation, and oscillations of electrical impulses in electrically excitable tissue.
By: acting on Na channels.
PHARMACOLOGY AND
PHARMACODYNAMICSClinically used local anesthetics consist of lipid-
soluble, substituted benzene ring linked to amine group via alkyl chain containing an amide or ester linkage.
• Type of linkage separates local anesthetics into either aminoamides (metabolized in liver) or aminoesters (metabolized in liver or by plasma cholinesterase).
PHARMACOKINETICSSystemic toxicity depends on blood levels of LA:
• End organs of main concern for toxicity are CV and CNS.
• Determinants of systemic absorption:
» Site of injection (intercostal > caudal > brachial plexus > sciatic/femoral)
» Dose.
» Physiochemical properties (lipid solubility, protein binding)
» Addition of epinephrine
Local anesthetics - Mechanism
Limit influx of sodium, thereby limiting
propagation of the action potential.
Local Anesthetics - Classes
Esters
Local anesthetics - Classes
Esters
Cocaine
Chloroprocaine
Procaine
Tetracaine
Amides
Bupivacaine
Lidocaine
Ropivacaine
Etidocaine
Mepivacaine
Bupivacaine
Amide
• Infiltration: use 0.25%, fast onset, 2- to 8-hr
duration, max dose 175 mg (225 mg with
epinephrine)
• Peripheral nerve block: use 0.25-0.5%, slow
onset, 4- to 12-hr duration, max dose 175 mg
(225 mg with epinephrine
Bupivacaine
Epidural anesthesia: Use 0.5-0.75%, moderate
onset, 2- to 5-hr duration, max dose 175 mg
(225 mg with epinephrine)
• Spinal anesthesia: Use 0.5-0.75%, fast onset, 1-
to 4-hr duration, max dose 20 mg
◼ levo (-) bupivacaine less cardiotoxic than
racemic bupivacaine, same profile.
Lidocaine
Amide
• Infiltration: use 0.5-1%, fast onset, 2- to 8-hr
duration, max dose 300 mg (500 mg with
epinephrine)
• Peripheral nerve block: use 1.0-1.5%, fast onset,
1- to 3-hr duration, max dose 300 mg (500 mg
with epinephrine)
Lidocaine
Epidural anesthesia: use 1.5-2%, fast onset, 1- to 2-hr duration, max dose 300 mg (500 mg with epinephrine)
• Spinal anesthesia: use 1.5-2%, fast onset, 0.5- to 1-hr duration, max dose 100 mg
• Topical anesthesia: use 4%, fast onset, 0.5- to 1-hr duration, max dose 300 mg
• IV regional: Use 0.25-0.5%, fast onset, 0.5-1 hr duration, max dose 300 mg
Ropivacaine
Amide
• Infiltration: use 0.2-0.5%, fast onset, 2- to 6-hr duration, max dose 200 mg
• Peripheral nerve block: use 0.5-1.0%, slow onset, 5- to 8-hr duration, max dose 250 mg
• Epidural anesthesia: Use 0.5-1.0%, moderate onset, 2- to 6-hr duration, max dose 200 mg
• less cardiac toxicity than bupivacaine
Local anesthetics - FormulationBiologically active substances are frequently administered as very dilute solutions which can be expressed as parts of active drug per
100 parts of solution (grams percent)
Ex.: 2% solution =
_2 grams__ = _2000 mg_ = __20 mg__
100 cc’s 100 cc’s 1 cc
Local Anesthetics - Allergy
◼ True allergy is very rare.
◼ Most reactions are from ester class - ester hydrolysis (normal metabolism) leads to formation of PABA - like compounds.
◼ Patient reports of “allergy” are frequently due to previous intravascular injections.
Local Anesthetics - Toxicity
Tissue toxicity - Rare
◼ Can occur if administered in high concentrations (greater than those used clinically)
◼ Usually related to preservatives added to solution
Systemic toxicity - Rare
◼ Related to blood level of drug secondary to absorption from site of injection.
◼ Range from lightheadedness, tinnitus to seizures and CNS/cardiovascular collapse
Local anesthetics - Duration
◼ Determined by rate of elimination of agent from the site injected
◼ Factors include lipid solubility, dose given, blood flow at site, addition of vasoconstrictors (does not reliably prolong all agents)
◼ Some techniques allow multiple injections over time to increase duration, e.g. epidural catheter
Local anesthetics - vasoconstrictors
Ratios
Epinephrine is added to local anesthetics in extremely
dilute concentrations, best expressed as a ratio of
grams of drug:total cc’s of solution. Expressed
numerically, a 1:1000 preparation of epinephrine
would be
1 gram epi
1000 cc’s solution
1000 mg epi
1000cc’s solution=
1 mg epi
1 cc=
Local anesthetics - vasoconstrictors
Therefore, a 1 : 200,000 solution of epinephrine would be
1 gram epi
200,000 cc’s solution=
1000 mg epi
200,000 cc’s solution
or
5 mcg epi
1 cc solution
Local anesthetics - vasoconstrictors
Vasoconstrictors should not be used in the following locations
◼ Fingers
◼ Toes
◼ Nose
◼ Ear lobes
◼ Penis
REGIONAL ANESTHESIA
Regional anesthesia - Definition
Rendering a specific area of the body, e.g. foot, arm, lower extremities,
insensate to stimulus of surgery or other instrumentation
Regional anesthesia - Uses
◼ Provide anesthesia for a surgical procedure
◼ Provide analgesia post-operatively or during labor and delivery
◼ Diagnosis or therapy for patients with chronic pain syndromes
Regional anesthesia - types
◼ Topical
◼ Local/Field
◼ Intravenous block (“Bier” block)
◼ Peripheral (named) nerve, e.g. radial n.
◼ Plexus - brachial, lumbar
◼ Central neuraxial - epidural, spinal
Topical Anesthesia
◼ Application of local anesthetic to mucous membrane - cornea, nasal/oral mucosa
◼ Uses :
• awake oral, nasal intubation, superficial surgical procedure
◼ Advantages :
• technically easy
• minimal equipment
◼ Disadvantages :
• potential for large doses leading to toxicity
Local/Field Anesthesia
◼ Application of LA subcutaneously to anesthetize distal nerve endings
◼ Uses:
• Suturing, minor superficial surgery, line placement, more extensive surgery with sedation
◼ Advantages:
• minimal equipment, technically easy, rapid onset
◼ Disadvantages:
• potential for toxicity if large field
IV Block - “Bier” block
◼ Injection of local anesthetic intravenously for anesthesia of an extremity
◼ Uses
• any surgical procedure on an extremity
◼ Advantages:
• technically simple, minimal equipment, rapid onset
◼ Disadvantages:
• duration limited by tolerance of tourniquet pain, toxicity
Peripheral nerve block
◼ Injecting local anesthetic near the course of a named nerve
◼ Uses:
• Surgical procedures in the distribution of the blocked nerve
◼ Advantages:
• relatively small dose of local anesthetic to cover large area; rapid onset
◼ Disadvantages:
• technical complexity, neuropathy
Plexus Blockade
◼ Injection of local anesthetic adjacent to a plexus, e.g cervical, brachial or lumbar plexus
◼ Uses :• surgical anesthesia or post-operative analgesia in
the distribution of the plexus
◼ Advantages:• large area of anesthesia with relatively large dose
of agent
◼ Disadvantages:• technically complex, potential for toxicity and
neuropathy.
Central neuraxial blockade - “Spinal”
◼ Injection of local anesthetic into CSF
◼ Uses:
• profound anesthesia of lower abdomen and extremities
◼ Advantages:
• technically easy (LP technique), high success rate, rapid onset
◼ Disadvantages:
• “high spinal”, hypotension due to sympathetic block, post dural puncture headache.
Central Neuraxial Blockade -
“epidural”
◼ Injection of local anesthetic in to the epidural space at any level of the spinal column
◼ Uses:
• Anesthesia/analgesia of the thorax, abdomen, lower extremities
◼ Advantages:
• Controlled onset of blockade, long duration when catheter is placed, post-operative analgesia.
◼ Disadvantages:
• Technically complex, toxicity, “spinal headache”
TOXICITY OF LOCAL ANESTHETICS
Rx of systemic toxicity is primarily supportive:
» Stop injection
» Administer oxygen
» Support ventilation
» Tracheal intubation and control ventilation if necessary
» Suppress seizure activity (thiopental, midazolam, propofol)
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