Principles of Anesthetics
Bucky Boaz, ARNP-C
Background
Carl Koller 1884 Freud colleague Eye surgery
Background
William Halsted 1885 Local injection of
cocaine for surgery Nerve block
Background
1884 Hall – Dentistry
1884 Zenfel – Ear
1890 Ritsert –
Benzocaine
1905 Einhorn and Braun –
Procaine 1930
Chlorprocaine 1941
Nils Lofgren Synthesized Xylocaine Changed to lidocaine
Physiochemical PropertiesAromaticSegment
Hydrophilic Segment
Amino-amine
Amino-ester
“Esters”
“Amines”
IntermediateChain
Amino-esters (“Esters”) Older class of drugs Derivatives of PABA (p-aminobenzoic acid) Hydrolyzed by serum cholinesterase
Examples Procaine (Novocaine) Cocaine Tetracaine Benzocaine
Physiochemical Properties
Amino-amines (“Amines”) Newer class of drugs Derivatives of aniline Hepatic degradation
Examples Lidocaine Bupivocaine (Marcaine, Sensoricaine, Polocaine) Mepivocaine (Carbocaine) Etidocaine Prilocaine
Physiochemical Properties
Physiologic Basis
Prevention of sodium influx across the nerve membrane
Sufficient anesthetic present prevents firing threshold from being obtained
Prevents action potential from forming No action potential, no impulse, therefore
conduction blockade End result is local anesthesia
Mechanism of ActionMechanism of Action
Onset
Dura
tion P
ote
ncy
Lipid solubility
Vasodilatation
Tissue pH
Concentration of drug
Protein binding
Vasodilatation
Mode of administration
Presence of vasoconstrictor
Inherent pKa
Myelination
Interspersed tissue
Dosage of drug
Ideal Anesthetic
Immediate onset Reversible Appropriate duration No permanent damage No tissue irritation / pain Wide therapeutic range Effective regardless of application
Topical Anesthesia
Intact Skin
Epidermis Avascular layer measuring
0.12 to 0.7 mm Barrier to diffusion of
topicals Dermis
Support structure Contains blood vessels
and nerve endings Anesthetic’s targeted site
of action
Agents
Lidocaine Cream EMLA Ethyl Chloride
Uses
Intact skin procedures Venopuncture Punch biopsies Lumbar puncture
Lidocaine Cream
30% lidocaine cream Saturated on gauze pad adherent to an elastic
patch 45 minutes minimum application time ½ hour anesthetic duration = 2 hour
application Effective and safe, but not practical
EMLA (Eutectic Mixture of Local
Anesthetics) 2.5% lidocaine and 2.5%
prilocaine 1-hour application time Maximum dose at 2-3 hours Depth of anesthesia
correlated to duration of application
Duration of 1-2 hours after removal
Hypersensitivity and systemic toxicity rare
Ethyl Chloride (C2H5CL)
Not an anesthetic, but a vapocoolant
Immediate anesthesia, but limited duration
Spray for 3 to 7 seconds Used for injections and
lancing small abscesses or boils
Not used for punch biopsies
Mucous Membranes
Nose, mouth, throat, tracheobronchial tree, esophagus, and genitourinary tract
Agents
Tetracaine Lidocaine Cocaine Benzocaine
Tetracaine
Effective and potent agent Long duration of action Downside = high toxicity Maximum adult dose of 50mg
Lidocaine
2% solution Swished inside the mouth then expectorated
5% liquid Applied with a swab
5% ointment Applied with a sterile gauze pad
Lidocaine
Indicated for painful, irritated, or inflamed mucous membranes of the mouth
2% good for aph-thous stomatitis and as adjunct before infraoral nerve block
5% ointment good for reducing pain during oral injection
Lidocaine
Precautions Impaired swallowing Numbness of the tongue Expectorate excess to avoid toxicity
Cocaine
Topical preparations available in 4% and 10% solutions and viscous formulations
Safe dose of 200mg (2 to 3 mg/kg) Apply for 5-6 minutes Works by vasoconstriction Coronary vasoconstriction with 2mg/kg
applied to the nasal mucosa
Benzocaine
Available in 14% to 20% liquid, gel, or spray Used to relieve pain in canker sores, cold
sores, other minor inflammation Very short duration and more allergenic Can be used prior to infraoral nerve block
Ophthalmic Anesthetics
Agents
Proparacaine Tetracaine
Proparacaine
0.5% solution Indicated for removal of
superficial foreign body 1 to 2 drops before
procedure Onset within 30 seconds Duration 15 minutes Have patient avoid
touching eye
Tetracaine
0.5% solution Onset, duration, and potency similar to
proparacaine Burning sensation worse and longer
Lacerations
TAC
TAC (tetracaine-adrenalin-cocaine) Used to anesthetize lacerations in children Wounds < 5cm Vasoconstrictor More effective on face and scalp
TAC
Advantages
DisadvantagesMinimum of 10-20 minute onset
Cost
Federal regulations
Painless No Distortion
Hemostasis Acceptance
Agents and Effectiveness
0.5% tetracaine, 1:2000 epinephrine (adrenalin), and 11.8% cocaine
Epinephrine 1:2000, cocaine 11.8% Tetracaine 0.25%, epi 1:4000, cocaine 5.9% Tetracaine 1.0%, epi 1:4000, cocaine 4% Lidocaine 4.0%, epi 1:1000, tetracaine 0.5% Gel by adding 0.15g methylcellulose to 1.5ml of epi
and cocaine solution
Application
Fill wound with TAC solution After 3 minutes, instill saturated gauze or
cotton into wound Leave in place 15-20 minutes SAFE dose maximum
Full strength TAC 0.09 ml/kg Tetracaine 50mg, cocaine 150-300mg
Adverse Reactions
Can lead to systemic toxicity from mucosal application
Gel form reduces runoff Ischemic complications
Precautions
Avoid in: CAD Uncontrolled HTN Seizures PVD Risk of Toxicity
Infiltration Anesthesia
Injection of anesthetic agent directly into tissue
Indications
Excision of skin lesions Incision of abscess Suturing of wounds
Advantages & Disadvantages
Advantages Quick and safe Provides hemostasis
Disadvantages Large dose for small area Distorts wounds
Choice of Agent
Lidocaine 0.5 to 1.0% Procaine 0.5% to 1.0% Bupivacaine 0.25%
Choice of Agent
AgentConcentration
(%)
Maximum Dose
Onset (min) Duration Adult (mg)
Pediatric (mg/kg)
Procaine 0.5-1.0 500 (600) 7.0 (9) 2-5 15-45 min
Lidocaine 0.5-1.0 300 (500) 4.5 (7) 2-5 1-2 hr
Bupivacaine 0.25 175 (225) 2.0 (3) 2-5 4-8 hr
Choice of Agent
Prolong duration by adding: Epinephrine Sodium bicarbonate Both Use bupivicaine
Advantages Disadvantages
1. Prolongs duration 1. Impairs host defenses--increases infection
2. Provides hemostasis 2. Delays wound healing
3. Slows absorption: Decreases agent toxicity potential Allows increased dose
3. Do not use for: Areas supplied by end arteries Patients"sensitive" to catecholamines
4. Increases level of blockade 4. Toxicity--catecholamine reaction
* Based on laboratory studies. For example, in patients taking MAO inhibitors.
Epinephrine Use
Bicarbonate Reduces pain of injection Mechanism unclear 1 cc 8.4 % bicarb : 9 cc lidocaine “Neut” 4.2 % bicarb (1cc:4cc) Precipitates in bupivicaine Shelf life : 1 wk (unref), 2 wks (refr)
Injection Technique
Bartfield JM, et al: Buffered lidocaine as a local anesthetic: An investigation of shelf life. Ann Emerg Med 21:24, 1992.
Lidocaine Bupivacaine Advantage
Onset 2-5 min 2-5 min Equal
Effectiveness (equianesthetic dose) Excellent Excellent Equal
Duration 1-2 hr 4-6 hr B
Infection potential No No Equal
Administration pain Less More L
Maximum volume --plain lidocaine Less More B
Maximum volume--epinephrine Less More B
Toxic potential Less cardiotoxic; equal CNS
More cardiotoxic; equal CNS
L
Comparison of 1% Lidocaine (L) and 0.25% Bupivacaine (B)--Infiltration Anesthesia
Injection Technique
Lowest concentration effective Prep wound first if possible Smallest needle available (27g) Use wound margin Subdermal injection Insert, then inject
Injection
Injection should be subdermal Bury the hub and inject as you withdraw Through wound edge
Warming No change in efficacy Less pain of injection Probably synergistic with buffering
Injection Technique
Brogan GX, et al: Comparison of plain, warmed and buffered lidocaine in wound repair. Ann Emerg Med; Aug. 1995.
Complications
Effects on wounds Systemic toxic reactions Catecholamine reaction Allergic reactions
Effect on Wounds
Wound healing Wound strength Avoid in poor healing
wounds Help prevent keloids
Wound infection Local injuries
Systemic Toxic Reaction
High Blood Levels Site and mode of administration Rate Dose of Concentration Addition of epinephrine Specific drug Clearance Maximum safe dose Inadvertent intravascular injection
Without epi 4.5 mg/kg 70 kg = 300 mg 30 cc (1 ½ bottles) of 1 % 15 cc (3/4 bottle) of 2 %
Maximum Dosage - Lido
With epi 7 mg/kg 70 kg = 500 mg 50 cc (2 ½ bottles)
of 1% 25 cc (1 ¼ bottles)
of 2%
Lidocaine
Dosage administered Packaging (% = g / dl)
1 %
20 cc
2 %
20 cc
4 %
20 cc
1 g/dl = 1000mg/100cc
= 10 mg/cc
200 mg/bottle
2 g/dl = 2000mg/100cc
= 20 mg/cc
400 mg/bottle
4 g/dl = 4000mg/100cc
= 40 mg/cc
800 mg/bottle
Systemic Toxic Reaction
Host Factors Hypoxia Acid-base status Protein binding Concomitant drugs
Catecholamine Reaction
Excess levels produce:
Tachycardia Palpitations
Hypertension Apprehension
Tremulousness Diaphoresis
Tachypnea Pallor
Anginal chest pain
Adverse Effects - Systemic
“But I’m allergic to the numbing
medicine”
Great,
now
what?
Adverse Effects - Systemic
Allergic reactions 1 – 2 % of total adverse reactions Esters
Large majorityPABA
AmidesRaremethlyparaben
Fisher,et al Anesthetic allergy clinic 208 patients with “allergy” to local anesthetic over
20 year period Intradermal testing 4 immed, 4 delayed 39 to “additives”
Fisher MM, Bowie CJ Alleged Allergy to Local Anesthetics Anaesth Intensive care 1997 Dec;25(6):611-4
Allergic Reactions
Recommendations
1. Define allergy vs. adverse rxn
2. Alternate class of anesthetics
3. Cardiac lidocaine
4. Test dose (0.1 cc SQ)
5. Diphenhydramine
Allergic Reactions
Allergic Reactions
Diphenhydramine Supplied as 5% solution (50 mg/cc) Tissue necrosis Must be diluted in NS
1 cc / 4 cc NS = 50 mg / 5 cc = 1 %1 cc / 9 cc NS = 50 mg / 10 cc = 0.5%
Allergic Reactions
Diphenhydramine 24 volunteers DPH 1% as effective as Lido 1% Injection more painful Safety profile not well established
Green SM, Rothrock SG, et al: Validation of diphenhydramine as a local anesthetic. Ann Emerg Med; June, 1994.
Allergic Reactions
Diphenhydramine 98 patients DPH 0.5 % vs. lidocaine 1 % No difference in pain of injection or efficacy,
except face
Ernest AA, et al. Lidocaine vs. diphenhydramine for laceration repair . Ann Emerg Med; Jun, 1994.
Allergic Reactions
Diphenhydramine Dbl blinded 2 cc of Lido 1 % vs. DPH 1 % 10 adult volunteers - pinprick
Conclusions No differences to 30 minutes, Lido better after 30 min Duration Lido (81 min) vs. DPH (42 min) 1/10 developed skin necrosis
Dire DJ. Double blinded comparison of lidocaine vs. diphenhydramine as a local anesthetic. Ann Emerg Med. 1993 ;22(9): 1419-1423.
Allergic Reactions
Recommendations
6. Normal saline
7. No anesthesia
8. Parenteral agents
9. General anesthesia
10. Nitrous oxide
11. Benzyl alcohol
Points to Remember
Esters and Amines Factors affecting MOA Types of anesthetics How applied Risks and Benefits Contraindications Adverse reactions
Questions?