Principles of Anesthetics

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Principles of Anesthetics
Bucky Boaz, ARNP-C
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Background

• Carl Koller
• 1884
• Freud colleague
• Eye surgery

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Background

• William Halsted
• 1885
• Local injection of cocaine for surgery
• Nerve block

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Background

• 1905
• Einhorn and Braun Procaine
• 1930
• Chlorprocaine
• 1941
• Nils Lofgren
• Synthesized Xylocaine
• Changed to lidocaine

• 1884
• Hall Dentistry
• 1884
• Zenfel Ear
• 1890
• Ritsert Benzocaine

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Physiochemical Properties
Aromatic Segment
Hydrophilic Segment
Intermediate Chain
Amino-amine
Amino-ester
Esters
Amines
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Physiochemical Properties

• Amino-esters (Esters)
• Older class of drugs
• Derivatives of PABA (p-aminobenzoic acid)
• Hydrolyzed by serum cholinesterase
• Examples
• Procaine (Novocaine)
• Cocaine
• Tetracaine
• Benzocaine

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Physiochemical Properties

• Amino-amines (Amines)
• Newer class of drugs
• Derivatives of aniline
• Hepatic degradation
• Examples
• Lidocaine
• Bupivocaine (Marcaine, Sensoricaine, Polocaine)
• Mepivocaine (Carbocaine)
• Etidocaine
• Prilocaine

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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

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Mechanism of Action
Lipid solubility Vasodilatation Tissue
pH Concentration of drug
Protein binding Vasodilatation Mode of
administration Presence of vasoconstrictor
Duration
Potency
Onset
Inherent pKa Myelination Interspersed
tissue Dosage of drug
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Ideal Anesthetic

• Immediate onset
• Reversible
• Appropriate duration
• No permanent damage
• No tissue irritation / pain
• Wide therapeutic range
• Effective regardless of application

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Topical Anesthesia
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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
• Anesthetics targeted site of action

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Agents

• Lidocaine Cream
• EMLA
• Ethyl Chloride

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Uses

• Intact skin procedures
• Venopuncture
• Punch biopsies
• Lumbar puncture

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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

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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

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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

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Mucous Membranes

• Nose, mouth, throat, tracheobronchial tree,
  esophagus, and genitourinary tract

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Agents

• Tetracaine
• Lidocaine
• Cocaine
• Benzocaine

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Tetracaine

• Effective and potent agent
• Long duration of action
• Downside high toxicity
• Maximum adult dose of 50mg

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Lidocaine

• 2 solution
• Swished inside the mouth then expectorated
• 5 liquid
• Applied with a swab
• 5 ointment
• Applied with a sterile gauze pad

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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

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Lidocaine

• Precautions
• Impaired swallowing
• Numbness of the tongue
• Expectorate excess to avoid toxicity

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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

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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

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Ophthalmic Anesthetics
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Agents

• Proparacaine
• Tetracaine

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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

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Tetracaine

• 0.5 solution
• Onset, duration, and potency similar to
  proparacaine
• Burning sensation worse and longer

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Lacerations
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TAC

• TAC (tetracaine-adrenalin-cocaine)
• Used to anesthetize lacerations in children
• Wounds lt 5cm
• Vasoconstrictor
• More effective on face and scalp

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TAC

• Advantages
• Disadvantages

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Agents and Effectiveness

• 0.5 tetracaine, 12000 epinephrine (adrenalin),
  and 11.8 cocaine
• Epinephrine 12000, cocaine 11.8
• Tetracaine 0.25, epi 14000, cocaine 5.9
• Tetracaine 1.0, epi 14000, cocaine 4
• Lidocaine 4.0, epi 11000, tetracaine 0.5
• Gel by adding 0.15g methylcellulose to 1.5ml of
  epi and cocaine solution

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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

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Adverse Reactions

• Can lead to systemic toxicity from mucosal
  application
• Gel form reduces runoff
• Ischemic complications

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Precautions

• Avoid in
• CAD
• Uncontrolled HTN
• Seizures
• PVD
• Risk of Toxicity

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Infiltration Anesthesia

• Injection of anesthetic agent directly into tissue

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Indications

• Excision of skin lesions
• Incision of abscess
• Suturing of wounds

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Advantages Disadvantages

• Advantages
• Quick and safe
• Provides hemostasis
• Disadvantages
• Large dose for small area
• Distorts wounds

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Choice of Agent

• Lidocaine 0.5 to 1.0
• Procaine 0.5 to 1.0
• Bupivacaine 0.25

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Choice of Agent
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Choice of Agent

• Prolong duration by adding
• Epinephrine
• Sodium bicarbonate
• Both
• Use bupivicaine

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Epinephrine Use
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Injection Technique

• Bicarbonate
• Reduces pain of injection
• Mechanism unclear
• 1 cc 8.4 bicarb 9 cc lidocaine
• Neut 4.2 bicarb (1cc4cc)
• Precipitates in bupivicaine
• Shelf life 1 wk (unref), 2 wks (refr)

Bartfield JM, et al Buffered lidocaine as a
local anesthetic An investigation of shelf life.
Ann Emerg Med 2124, 1992.
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Comparison of 1 Lidocaine (L) and 0.25
Bupivacaine (B)--Infiltration Anesthesia
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Injection Technique

• Lowest concentration effective
• Prep wound first if possible
• Smallest needle available (27g)
• Use wound margin
• Subdermal injection
• Insert, then inject

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Injection

• Injection should be subdermal
• Bury the hub and inject as you withdraw
• Through wound edge

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Injection Technique

• Warming
• No change in efficacy
• Less pain of injection
• Probably synergistic with buffering

Brogan GX, et al Comparison of plain, warmed
and buffered lidocaine in wound repair. Ann
Emerg Med Aug. 1995.
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Complications

• Effects on wounds
• Systemic toxic reactions
• Catecholamine reaction
• Allergic reactions

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Effect on Wounds

• Wound healing
• Wound strength
• Avoid in poor healing wounds
• Help prevent keloids
• Wound infection
• Local injuries

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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

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Maximum Dosage - Lido

• Without epi
• 4.5 mg/kg
• 70 kg 300 mg
• 30 cc (1 ½ bottles) of 1
• 15 cc (3/4 bottle) of 2

• With epi
• 7 mg/kg
• 70 kg 500 mg
• 50 cc (2 ½ bottles) of 1
• 25 cc (1 ¼ bottles) of 2

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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
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Systemic Toxic Reaction

• Host Factors
• Hypoxia
• Acid-base status
• Protein binding
• Concomitant drugs

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Catecholamine Reaction

• Excess levels produce

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Adverse Effects - Systemic
But Im allergic to the numbing medicine
Great, now what?
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Adverse Effects - Systemic

• Allergic reactions
• 1 2 of total adverse reactions
• Esters
• Large majority
• PABA
• Amides
• Rare
• methlyparaben

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Allergic Reactions

• 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
Dec25(6)611-4
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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

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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

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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.
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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.
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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.
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Allergic Reactions

• Recommendations
• 6. Normal saline
• 7. No anesthesia
• 8. Parenteral agents
• 9. General anesthesia
• 10. Nitrous oxide
• 11. Benzyl alcohol

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Points to Remember

• Esters and Amines
• Factors affecting MOA
• Types of anesthetics
• How applied
• Risks and Benefits
• Contraindications
• Adverse reactions

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Questions?