Transcript Principles of Anesthesia

Principles of Anesthetics
Bucky Boaz, ARNP-C
Background
 Carl Koller
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1884
Freud colleague
Eye surgery
Background
 William Halsted
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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 Properties
Aromatic
Segment
Intermediate
Chain
Hydrophilic
Segment
Amino-ester
Amino-amine
“Esters”
“Amines”
Physiochemical Properties
 Amino-esters (“Esters”)
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Older class of drugs
Derivatives of PABA (p-aminobenzoic acid)
Hydrolyzed by serum cholinesterase
 Examples
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Procaine (Novocaine)
Cocaine
Tetracaine
Benzocaine
Physiochemical Properties
 Amino-amines (“Amines”)
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Newer class of drugs
Derivatives of aniline
Hepatic degradation
 Examples
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Lidocaine
Bupivocaine (Marcaine, Sensoricaine, Polocaine)
Mepivocaine (Carbocaine)
Etidocaine
Prilocaine
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 Action
Protein binding
Lipid solubility
Vasodilatation
Vasodilatation
Mode of administration
Tissue pH
Presence of
vasoconstrictor
Concentration of drug
Onset
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
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Avascular layer measuring
0.12 to 0.7 mm
Barrier to diffusion of
topicals
 Dermis
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Support structure
Contains blood vessels
and nerve endings
Anesthetic’s targeted site
of action
Agents
 Lidocaine Cream
 EMLA
 Ethyl Chloride
Uses
 Intact skin procedures
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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
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Swished inside the mouth then expectorated
 5% liquid
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Applied with a swab
 5% ointment
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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
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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
Painless
Hemostasis
No Distortion
Acceptance
 Disadvantages
Minimum of 10-20 minute onset
Cost
Federal regulations
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
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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:
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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
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Quick and safe
Provides hemostasis
 Disadvantages
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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
Maximum Dose
Adult (mg)
Pediatric
(mg/kg)
Onset
(min)
Duration
Concentration
Agent
(%)
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:
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Epinephrine
Sodium bicarbonate
Both
Use bupivicaine
Epinephrine Use
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.
Injection Technique
 Bicarbonate
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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)
Bartfield JM, et al: Buffered lidocaine as a local anesthetic: An
investigation of shelf life. Ann Emerg Med 21:24, 1992.
Comparison of 1% Lidocaine (L) and 0.25%
Bupivacaine (B)--Infiltration Anesthesia
Lidocaine
Bupivacaine
Advantage
2-5 min
2-5 min
Equal
Excellent
Excellent
Equal
1-2 hr
4-6 hr
B
No
No
Equal
Administration pain
Less
More
L
Maximum volume --plain lidocaine
Less
More
B
Maximum volume--epinephrine
Less
More
B
Less cardiotoxic;
equal CNS
More cardiotoxic;
equal CNS
L
Onset
Effectiveness (equianesthetic dose)
Duration
Infection potential
Toxic potential
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
Injection Technique
 Warming
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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.
Complications
 Effects on wounds
 Systemic toxic reactions
 Catecholamine reaction
 Allergic reactions
Effect on Wounds
 Wound healing
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Wound strength
Avoid in poor healing
wounds
Help prevent keloids
 Wound infection
 Local injuries
Systemic Toxic Reaction
 High Blood Levels
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Site and mode of administration
Rate
Dose of Concentration
Addition of epinephrine
Specific drug
Clearance
Maximum safe dose
Inadvertent intravascular injection
Maximum Dosage - Lido
 Without epi
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4.5 mg/kg
70 kg = 300 mg
30 cc (1 ½ bottles) of 1 %
15 cc (3/4 bottle) of 2 %
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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%
2%
4%
20 cc
20 cc
20 cc
1 g/dl =
1000mg/100cc =
10 mg/cc
2 g/dl =
2000mg/100cc =
20 mg/cc
4 g/dl =
4000mg/100cc =
40 mg/cc
200 mg/bottle
400 mg/bottle
800 mg/bottle
Systemic Toxic Reaction
 Host Factors
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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
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1 – 2 % of total adverse reactions
Esters
Large majority
 PABA
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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 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
 Diphenhydramine
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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
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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
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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
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Dbl blinded
2 cc of Lido 1 % vs. DPH 1 %
10 adult volunteers - pinprick
 Conclusions
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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?