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LOCAL ANESTHETICS AND REGIONAL ANESTHESIA
LOCAL ANESTHETICS AND REGIONAL ANESTHESIA
Local Anesthetics- HistoryLocal Anesthetics- History
• 1860 - cocaine isolated from erythroxylum coca• Koller - 1884 uses cocaine for topical anesthesia• Halsted - 1885 performs peripheral nerve block
with local• Bier - 1899 first spinal anesthetic
Local Anesthetics - DefinitionLocal Anesthetics - Definition
A substance which reversibly inhibits nerve conduction when applied directly to tissues at non-toxic concentrations
Local anesthetics - MechanismLocal anesthetics - Mechanism
Limit influx of sodium, thereby limiting propagation of the action potential.
Local Anesthetics - ClassesLocal Anesthetics - Classes
Esters
Local anesthetics - Classes (Rule of “i’s”)
EstersCocaineChloroprocaineProcaineTetracaine
Am”i”desBupivacaineLidocaineRopivacaineEtidocaineMepivacaine
Local anesthetics - Formulation
Biologically 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 enough 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 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
Vasoconstrictors
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 local 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”
QUESTIONS?