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?