Injectable Anesthetics Flashcards

1
Q

Pros of injectable anesthetics

A

Rapid onset of anesthesia Rapid control of airway IM injection possible Minimal equipment

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2
Q

Cons of injectable anesthetics

A

Minimal conrol over waking Controlled substances

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3
Q

Injectable anesthetics

A

Barbiturates Propofol Alphaxalone Dissociative agents Etomidate

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4
Q

Types of barbiturates

A

Thiobarbiturates Oxybarbiturates

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5
Q

Thiobarbiturates

A

Thiopental (III) Ultrashort acting 20 minutes

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6
Q

Oxybarbiturates (type & how long lasts)

A

Phenobarbital (IV) -~12hours Pentobarbital (II) - ~1-2 hours Methohexital (IV) - ~20 mins

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7
Q

Barbiturate mechanism of action

A

GABA, GA?, BDZ , Cloride channel (**PICTURE**)

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8
Q

Barbiturate Pharmacologic effects on CNS

A

Dose-dependent CNS depression Decreased intracranial pressure (except methohexital)

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9
Q

Barbiturate Dose-dependent CNS depression

A

Sedation Hypnosis Anesthesia Coma Death

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10
Q

Barbiturate Pharmacologic effects on Respiratory system

A

Dose-dependent respiratory depression Oral administration has minimal respiratory effects

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11
Q

Barbiturate Dose-dependent respiratory depression

A

Transient apnea Intubate & assist with breathing as necessary Cats more sensitive than other species

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12
Q

What species are more sensitive to respiratory depression by barbiturates?

A

Cats! Meow

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13
Q

Barbiturates Pharmacologic effects on CV system

A

Hypotension Myocardial sensitization to catecholamines

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14
Q

Barbiturates - Hypotension

A

Decreased stroke volume & cardiac contractility Vasodilation Reflex tachycardia

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15
Q

Barbiturates - Myocardial sensitization to catecholamines

A

Arrhythmias Vagal stimulation

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16
Q

Barbiturates - Pharm. effects on skeletal system

A

Decreased motor end-plate sensitivity to ACh -Incomplete relaxation of abdominal muscles -Laryngeal reflexes preserved

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17
Q

Barbiturates - Pharm. effects on Body Temperature

A

Hypothermia due to peripheral vasodilation and decreased basal metabolic rate

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18
Q

Barbiturates - Pharm. effects on renal system

A

Hypotension –> reduction in GFR can lead to oliguria Stimulation of ADH

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19
Q

Barbiturates - Pharm effects on Reproductive system

A

Depression of uterine contractions & fetal respiration

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20
Q

Barbiturates - Administration

A

Given IV (usually 1/3 to 1/2 the dose as a bolus)

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21
Q

Phenobarbital Administration

A

For sedation & anticonvulsive Orally PO bioavailability of 90%

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22
Q

Barbiturates - Distribution

A

Widely distributed to all tissues, including CNS *Very Lipid-soluble* Protein binding variable

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23
Q

Barbiturates - Redistribution

A

Can be seen Animal wakes up before drug is metabolized (adipose depot)

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24
Q

Barbiturates - Distribution Effect of systemic acidosis

A

Systemic acidosis may increase distribution

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25
Q

Barbiturates - Protein binding

A

Thio >70% Pento ~45%

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26
Q

Barbiturate - Metabolism @Liver

A

Hydroxylation in the liver

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27
Q

Barbiturate - Metabolism @Kidney & Brain

A

Inactivation

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28
Q

Barbiturate metabolism in greyhounds

A

Exhibit prolonged effect Deficient in oxidative enzymes for metabolism

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29
Q

What is the biggest hepatic microsomal enzyme inducer?

A

Phenobarbital, used long term

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30
Q

Barbiturate - Excretion

A

Renal excretion Increased by alkalinization of urine

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31
Q

What increased barbiturate excretion?

A

Alkalinization of urine

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32
Q

Barbiturate - Clinical uses

A

Sedation Induction of general anesthesia Treating CNS excitatory toxicants Anticonvulsants Euthanasia

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33
Q

Barbiturates in sedation

A

Phenobarbital - oral

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34
Q

Barbiturate for induction of general anesthesia

A

Thiopental (IV)

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35
Q

Barbiturate for treating CNS excitatory toxicants

A

Phenobarbital, pentobarbital (IV)

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36
Q

Barbiturate for anticonvulsant, prevention & treatment

A

Phenobarbital (Oral, IV)

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37
Q

Barbiturate for euthanasia

A

Pentobarbital (IV)

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38
Q

Barbiturate - Adverse effects

A

Respiratory depression (post-induction apnea) Cardiac depression/ hypotension Cardiac arrhythmias (esp. thiobarbiturates) Splenic enlargement (RBC sequestration) Long recovery Hyperalgesia (at sub-anesthetic doses) NOT analgesic

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39
Q

Barbiturate cautions - pre-existing conditions

A

Caution with: Cardiac disease, hypotension, shock Liver or Kidney disease Hypoproteinemia

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40
Q

Barbiturate caution- Mode of administration

A

Do not give IM/SC/Perivascular/Intraarterial Causes tissue damage

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41
Q

Barbiturate caution in “topping up”

A

Redistribution

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42
Q

Better options than barbiturates are recommended for these animals:

A

Greyhounds & sighthounds Pregnant animals Splenectomy

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43
Q

Barbiturate - drug interactions

A

CNS depressants Muscle relaxants Chloramphenicol - may prolong barbiturate

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44
Q

Thiopental (Pentothal) Pros

A

Reliable, inexpensive

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45
Q

Thiopental (Pentothal) Species doses: Horse, Dog, Cat

A

Horse: 10% solution, pH 12 Dog: 2.5% solution, pH 11 Cats: 1.25% solution, pH 9.5

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46
Q

Thiopental (Pentothal) Lasts how long?

A

Ultra-short acting - ~20mins

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47
Q

Thiopental (Pentothal) Shelf life?

A

Short shelf life once reconstituted

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48
Q

Thiopental (Pentothal) Wide/Narrow therapeutic index

A

Narrow therapeutic index

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49
Q

Thiopental (Pentothal) Lipid soluble?

A

Very highly lipophilic Redistribution can be significant

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50
Q

What does this picture depict?

A

Redistribution with thiopental

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51
Q

Methohexital (Brevital) Former use

A

Formerly for IV induction in greyhounds (now other agents used)

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52
Q

Methohexital (Brevital) Effect time

A

Ultra-short acting (~10mins)

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53
Q

Methohexital (Brevital) Actions

A

Excitement on induction and recovery

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54
Q

Methohexital (Brevital) Effects on respiratory system

A

Significant respiratory depression

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55
Q

Pentobarbital Use

A

(Nembutal, Euthasol) Usually only for euthanasia

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56
Q

Pentobarbital Administration

A

Can be used for IV induction in sheep/goats -Metabolize it faster than other species

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57
Q

Pentobarbital Effect time

A

Short acting 1-2 hours

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58
Q

Pentobarbital When is it used for long-term sedation?

A

In treatement of CNS excitatory toxicants ex- Metaldehyde poisoning

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59
Q

Propofol Two sub-types

A

Propoflo Propoflo 28

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60
Q

Propoflo Similar to what drug? How do they differ?

A

Similar to thiopental -Less hangover, faster induction/recovery

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61
Q

Propoflo Emulsion

A

Emulsion containing egg lecithin & soybean oil -Ideal for bacterial growth -One of few white liquids ok for IV -Once opened, discard in 24 hr

62
Q

Propoflo 28

A

Benzyl alcohol preservative -Once opened, stable at room temp for 28 days

63
Q

Propofol Mechanism of action

A

Potentiates GABAa receptors

64
Q

Propofol Pharm effects on CNS

A

Dose-dependent CNS depression Decreases intracranial & ocular pressure Decreases metabolic oxygen consumption Maintains cerebral autoregulation

65
Q

Propofol Dose-dependent CNS depression

A

Sedation–> Hypnosis–> Anesthesia–> Coma–> Death

66
Q

Propofol What aspect is good for CNS disease patients

A

Decreases intracranial & ocular pressures

67
Q

Propofol Pharm effects on CV system

A

Hypotension Sensitization of heart to epinephrine

68
Q

Propofol Hypotension effects

A

Vasodilation without reflex tachycardia

69
Q

Propofol What effect has the potential to cause arrhythmias

A

The sensitization of the heart to epinephrine

70
Q

Propofol Pharm effects on respiratory system

A

Dose dependent respiratory depression Rate-dependent apnea

71
Q

Propofol What can dose dependent respiratory depression cause

A

Mild hypercapnea & acidosis

72
Q

Propofol What increases rate-dependent apnea?

A

More rapid administration

73
Q

Propofol Pharm effects on muscle

A

Decreases motor end-plate sensitivity to ACh -Laryngeal reflexes decreased -Myoclonic movements may be seen

74
Q

Propofol Pharmacokinetics Administration

A

Given IV (slowly to effect)

75
Q

Propofol Pharmacokinetics Distribution

A

Widely distributed to all tissues Lipid-soluble drug

76
Q

Propofol Pharmacokinetics Redistribution

A

To muscle then to fat

77
Q

Propofol Pharmacokinetics Metabolism

A

Rapid Hepatic & Extrahepatic (lungs) Greyhounds - prolonged effect, lack oxidative enzymes Conjugation with glucuronide & sulfate

78
Q

Propofol Pharmacokinetics Excretion

A

Metabolites excreted in urine

79
Q

Propofol Clinical uses

A

Sedation Anesthesia Anticonvulsant Appetite stimulant?

80
Q

Propofol Anesthesia

A

Fast induction (<1 minute) and recovery (5-8 min) Maintenance (CRI) Repeated boluses (no accumulation)

81
Q

Propofol Cautions Respiratory risks

A

Potential for respiratory depression & hypotension

82
Q

Propofol Cautions Given too rapidly

A

Rate-dependent apnea

83
Q

Propofol Cautions Injection site

A

Local pain on injection Use large veins Running IV fluids Local anesthetics

84
Q

Propofol Cautions Appendage problems

A

Front leg stiffness Paddling sometimes seen

85
Q

Propofol Cautions Cats

A

Heinz body formation with repeated doses >5 days

86
Q

Propofol Cautions Horses

A

Excitement at induction in some horses

87
Q

Alphaxalone

A

AKA Alfaxan Neurosteroid, analog of progesterone

88
Q

Alphaxalone Bind to steroid receptors?

A

Does not bind to usual steroid receptors (glucocorticoid, mineralocorticoid, sex hormone receptors)

89
Q

Alphaxalone Controlled?

A

Class 4 controlled substance in US Approved & available within past year

90
Q

Alphaxalone Administration

A

Labelled for IV use -Has been used IM too

91
Q

Alphaxalone Recovery

A

Agitation seen on recovery, especially if no pre-med

92
Q

Alphaxalone Effect on histamine

A

Histamine release with older products (contained cremophore excipient)

93
Q

Alphaxalone Mechanism of action

A

Potentiates GABAa receptors

94
Q

Alphaxalone Pharm effect on CNS

A

Dose-dependent CNS depression (simillar to propofol, less severe) Likely no analgesia

95
Q

Alphaxalone Pharm effects on Respiratory system

A

Rate-dependent apnea (given slowly)

96
Q

Alphaxalone Pharm effects on muscle system

A

Good muscle relaxation

97
Q

Alphaxalone Pharm effects on CV system

A

Some dose-dependent cardiovascular depression (potentially less than propofol) May decrease epinephrine-induced arrhythmia

98
Q

Alphaxalone Clinical uses -Describe induction, maintenance, accumulation

A

Anesthesia -Fast induction ~1min Recovery ~5-8 min Maintenance CRI can be used No accumulation with repeated boluses

99
Q

Alphaxalone Cautions - Liver dysfunction

A

May require dosage adjustment

100
Q

Alphaxalone Cautions- Rapid administration

A

Respiratory depression

101
Q

Alphaxalone Caution - Recovery

A

Agitation seen on recovery

102
Q

Dissociative Agents Characterize their anesthesia

A

Catalepsy Amnesia Analgesia (not always completely unconscious)

103
Q

Dissociative Agents Why the name?

A

Humans felt “dissociated” or unaware of their environment and what was being done to them

104
Q

Dissociative Agents Describe the state of patient

A

State of unresponsiveness to painful stimuli Eyes remain open Skeletal muscle hypertonicity Swallowing reflexes persist

105
Q

Dissociative Agents

A

Ketamine Tiletamine (with zolazepam (Telazol))

106
Q

Dissociative Agents Classification

A

Scheduled drug Class III

107
Q

Dissociative Agents Mechanism of action

A

NMDA receptor channel blockade -Inhibits activation of ligand-gated ion channels by glutamate & other effects

108
Q

Dissociative Agents Pharm effects on CNS

A

Thalamocortical depression Limbic system activation/depression Catalepsy Partial consciousness Analgesia

109
Q

Dissociative Agents Catalepsy

A

Need to use muscle relaxants Pharyngeal and laryngeal reflexes maintained Eyes open, pupils dilated (cover eyes, ointment)

110
Q

Dissociative Agents Pharm effects on CV system

A

Stimulation Direct depressant effect on myocardium

111
Q

Dissociative Agents CV stimulation

A

Centrally mediated -Increased sympathetic tone -Decreased parasympathetic tone Increased cardiac output, CVP, HR

112
Q

Dissociative Agents Direct myocardium depressant

A

Overridden by central stimulation, overall minimal CV depression

113
Q

Dissociative Agents Pharm effects on respiratory system

A

Low anesthetic doses stimulat respiration Large doses depress respiration Bronchodilation Increased tracheobronchial secretions

114
Q

Dissociative Agents Pharm effects on GI

A

Stimulation of salivary secretions

115
Q

Dissociative Agents Absorption

A

Usually IV Rapidly absorbed after IM Good oral/rectal Rarely epidurally/intrathecally

116
Q

Dissociative Agents Distribution

A

Widely distributed to all tissues Lipid soluble Undergoes redistribution

117
Q

Dissociative Agents Metabolism

A

Demethylation to Norketamine -Less potent, active metabolite Oxidation then glucuronidation in liver (dogs) and sulfation (cats)

118
Q

Dissociative Agents What species involve sulfation during metabolism?

A

Cats. They excrete unchanged drug

119
Q

Dissociative Agents Excretion

A

Metabolites excreted in urine Cats excrete unchanged drug in urine

120
Q

Dissociative Agents Clinical uses

A

Chemical restraint Induction of anesthesia Anesthesia for minor surgery Analgesia (MLK drip)

121
Q

Dissociative Agents Problem for asthmatic patients

A

Cardiovascularly unstable for asthmatic patients

122
Q

Dissociative Agents Caution- High doses

A

Respiratory depression at high doses

123
Q

Dissociative Agents Caution - Muscle & CNS

A

Muscle tremors & hypertonicity CNS stimulation & convulsions Vomiting/ hypersalivation Prolonged recovery

124
Q

Dissociative Agents Caution - IM injection

A

Pain associated

125
Q

Dissociative Agents Caution - Predisposing problems

A

Cardiac disease Hypertension Liver disease Kidney disease Pregnancy - C-sections Head Trauma Glaucoma Seizures

126
Q

Dissociative Agents Tiletamine/ Zolazepam

A

Tiletamine (Dissociative) + Zolazepam (benzodiazepine) Combined in a fixed ratio

127
Q

Dissociative Agents Tiletamine/Zolazepam Caution with Dogs

A

Dogs metabolize zolazepam more rapidly Issues on recovery: Muscle rigidity, emergence delerium, convulsions

128
Q

Dissociative Agents Tiletamine/Zolazepam Contraindications

A

Animals with pancreatitis Severe cardiac disease Severe pulmonary disease Rabbits- renal toxicity Tigers

129
Q

Etomidate

A

AKA amidate Non-barbiturate (imidazole) anesthetic

130
Q

Etomidate Solution

A

2% solution in 35% propylene glycol (lipid vehicle not available in USA)

131
Q

Etomidate Solubility

A

Water soluble in acidic pH Lipid soluble at physiologic pH (7.4)

132
Q

Etomidate Therapeudic index

A

Wide

133
Q

Metomidate/ Aquacalm

A

Fish anesthetic

134
Q

Etomidate Mechanism of action

A

Potentiates GABAa receptors

135
Q

Etomidate Pharm effects on CNS

A

Dose-dependent depression Decrease intracranial/ocular pressure Decreases cerebral blood flow Decreases metabolic oxygen consumption Maintains cerebral autoregulation Increases activity at epileptogenic foci

136
Q

Etomidate Pharm effects on CV system

A

No significant depression

137
Q

Etomidate Pharm effects on Respiratory system

A

Transient apnea after induction

138
Q

Etomidate Pharm effects on skeletal system

A

Rigidity Myoclonus

139
Q

Etomidate Pharm effects on other systems

A

Transient adrenal suppression 11-beta-hydroxylase

140
Q

Etomidate Administration

A

IV

141
Q

Etomidate Distribution

A

Bound to plasma proteins ~75% Redistribution occurs

142
Q

Etomidate Metabolism

A

In liver Hydroxylation & glucuronidation

143
Q

Etomidate Excretion

A

Excreted in urine (85%) and bile (15%)

144
Q

Etomidate Clinical uses

A

Induction of anesthesia Not used as a CRI

145
Q

Etomidate Induction of anesthesia

A

Useful in patients with CV instability Excitement or induction (use with premed)

146
Q

Etomidate Not used as CRI

A

Adrenocortical suppression Propylene glycol (hyperosmolar) - can lead to hemolysis

147
Q

Etomidate Cautions - Cats

A

Cats more susceptible to hemolysis

148
Q

Etomidate Contraindications

A

Avoid in hypoadrenocorticism, causes adrenocortical suppression Avoid if generalized tonic-clonic seizures

149
Q

Etomidate Cautions

A

-Liver/Kidney disease -Caution with neuromuscular blockers -Myoclonus - use with premed

150
Q

Etomidate Injection site

A

Pain at injection site from propylene glycol