Transcript LOCAL ANESTHETICS AND REGIONAL ANESTHESIA

LOCAL ANESTHETICS AND REGIONAL
ANESTHESIA
Local 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 - Definition
A substance which reversibly inhibits
nerve conduction when applied directly to
tissues at non-toxic concentrations
Local anesthetics - Mechanism
Limit influx of sodium, thereby limiting propagation of the
action potential.
Local Anesthetics - Classes
Esters
Local anesthetics - Classes (Rule of “i’s”)
Esters
Cocaine
Chloroprocaine
Procaine
Tetracaine
Am”i”des
Bupivacaine
Lidocaine
Ropivacaine
Etidocaine
Mepivacaine
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
=
or
5 mcg epi
1 cc solution
200,000 cc’s 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
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•
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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, postoperative analgesia.
• Disadvantages:
– Technically complex, toxicity, “spinal headache”
QUESTIONS?