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?