Clinical Pharmacology of Anesthetics Flashcards
1
Q
what are the injectable anesthetics used in vet med (5)
A
- propofol
- steroid anesthetics: alfaxalone
- barbiturates: thiopentone, pentobarbitone
- imidazole derivatives: etomidate
- dissociative agents: ketamine, tiletamine (+ zolazepam = zoletil)
2
Q
what is the onset of propofol
A
rapid
3
Q
what is the duration of propofol
A
short duration IV anesthetic
4
Q
what is the structure of propofol
A
hindered phenol
5
Q
what is the mechanism of propofol
A
potentiates GABA
6
Q
what is the formulation of propofol
A
oil in water emulsion
soyabean oil, egg lecithin & glycerol
7
Q
what is the route of administration of propofol
A
IV
8
Q
what are the pharmacokinetics of propofol
A
highly protein bound
rapid metabolism in liver + lungs, kidneys, blood?
9
Q
what is the recovery from propofol initially from
A
due to redistribution
10
Q
do cats or dogs have a more rapid metabolism of propofol
A
slower in cats because less able to conjugate with glucuronide –> avoid IV infusions
11
Q
what are the effects of propofol on the CNS (3)
A
- rapid loss of consciousness (~5 min)
- reduced intracranial pressure (ICP)
- anticonvulsant action
12
Q
what are the effects of propofol on the CVS (2)
A
- vasodilation & transient fall in BP
- mild myocardial depression at high doses
13
Q
what are the effects of propofol on respiratory system
A
- post-induction apnea
- occasional cyanosis at induction
14
Q
what other effects can propofol have
A
- pain on injection?
- occasional muscle twitching/hypertonus
- heinz body anemia in cats (oxidative damage to RBCs)
15
Q
what is propofol licensed for
A
IV admin in dogs and cats
16
Q
what are the uses of propofol
A
17
Q
what is propofol use cautioned in (3)
A
- shocked/hypovolemic patients
- cats with hepatic dysfunction
- cats requiring repeat anesthetics
18
Q
what are the 2 formulations of propofol
A
- preservative free: in use shelf life 6 hours
- with preservative: propofol plus with benzyl alcohol
19
Q
what is the propofol with preservatives contraindicated for
A
prolonged infusion (>30 mins)
dont give >24mg/kg per anesthetic
20
Q
what is the structure of alfaxalone
A
steroid anesthetic
21
Q
what is the mechanism of alfaxalone
A
potentiates GABA
22
Q
what is the formulation of alfaxalone
A
solubilized in cyclodextrin
some have preservatives
23
Q
what is alfaxalone
A
rapid onset, short duration injectable anesthetic with high therapeutic index
24
Q
what are the admin routes for alfaxalone
A
IV (IM & SC)
25
how is the protein binding of alfaxalone vs propofol
lower protein binding
26
what is the recovery from alfaxalone initially due to
redistribution
27
how is alfaxalone metabolized
liver
28
is alfaxalone suitable for TIVA in dogs and cats
yes
29
what are the effects of alfaxalone on CNS
rapid loss of consciousness
30
what are the effects of alfaxalone on the CVS
mild hypotension at clinical doses, primarily due to vasodilation
31
what are the effects of alfaxalone on respiratory system
post-induction apnea (less frequent compared to propofol)
32
how is the recovery from alfaxalone
can be poor quality, esp if limited/poor premedication
33
what is the clinical use of alfaxalone
1. admin IV to induce anesthesia
2. admin IV (intermittent bolus or continuous infusion) to maintain anethesia in dogs & cats
3. IM/SC for sedation (not authorized, large volume of injection)
34
what is ketamine
dissociative anesthetic and analgesic
35
what is the mechanism of ketamine
NMDA receptor antagonist
36
what is the formulation of ketamine
acidic pH
37
what are the pharmacokinetics of ketamine
rapid hepatic metabolism
38
what are the routes of admin of ketamine
IV, IM, SC
39
which species is TIVA ketamine suitable for
horses
40
what effects do dissociative anesthesia ketamine cause (5)
1. sensory loss with analgesia
2. increased muscle tone
3. eyes open +/- slow nystagmus
4. active relfexes including laryngeal/pharyngeal reflexes
5. less profound CVS & resp depression
41
what are the effects of ketamine on the CNS (4)
1. loss of consciousness with analgesia
2. increased ICP
3. convulsions in dogs/horses (esp if used as sole agent)
4. hallucinations/emergence delirium
42
what are the effects ketamine has on the musculoskeletal system
increased muscle tone
43
what are the effects ketamine has on the CVS
1. in vitro direct -ve inotropic effect
2. in vivo increased sympathetic tone --\> increased HR, contractility, CO & BP
44
what are the effects of ketamine on the respiratory system (2)
1. transient apnea possible with IV admin (ventilation usually well maintained when given by SC or IM)
2. laryngeal and pharyngeal relfexes maintained?
45
what are the clinical uses of ketamine (3)
1. to induce anesthesia in dogs, cats, horses + combine with benzodiazepams & injected IV
2. to induce anesthesia & maintain anesthesia (~30 mins) in dogs and cats + a2 agonist and butorphanol & injected IM ("triple combo")
3. to provide analgesia in dogs and cats (lower dose IM or IV)
46
what are the cautions of ketamine (3)
1. elavated intracranial pressure
2. history of seizures
3. pre-existing tachycardia
47
when might you use TIVA
1. where inhalational agents not available
2. where airway cannot be shared (bronchoscopy, some airway surgeries)
48
what are examples of TIVA in dogs
propofol or alfaxalone are suitable
poor reflex suppression so can combine with analgesics
49
what are TIVA examples in cats
only alfaxalone suitable
50
what are examples of TIVA in horses
triple drip
alpha2 agonist plus GGE plus ketamine
field anesthesia
51
how do you select the right agent
little to chose between propofol, alfaxalone
52
when would ketamine be used
1. IM anesthesia required --\> aggressive patient, no IV access, no facilities for delivering inhaled agents
2. hemodynamic instability is present
53
what would reduce CVS depression in cases with hemodynamic instability
co-induction
54
how is anesthesia maintained
1. TIVA or IM triple combo
2. inhalational agents
55
what are the advantages of inhalational anesthetic agents
delivery/elimination depends on ventilation --\> rapid adjustment of anesthetic depth
56
what are the disdvantages of inhalational anesthetic agents (2)
1. equipment required: ET tube, carrier gas, vaporizer, breathing system
2. environmental pollution
57
what are inhalational agents
1. isoflurane
2. sevoflurane
58
what is the minimum alveolar concentration
steady state minimum alveolar concentration of anesthetic required to prevent gross purposeful movement in response to noxious stimulation in 50% of test subjects
compares the potency of different inhaled anesthetics
59
which is more potent isoflurane or sevoflurane
sevoflurane more potent (higher MAC)
60
what is the oil:gas partition coefficient
measure lipid solubility
high oil:gas PC confers high potency
61
what is the blood:gas partition coefficient
measures solubility in the blood
low blood solubility confers to rapid onset, recovery & rate of change of anesthetic depth
62
which has a higher blood:gas coefficient between isoflurane and sevoflurane
isoflurane
63
how are inhalational agents metabolized and eliminated
exhalation
liver metabolism
can produce toxic metabolites
64
compare the differences of isoflurane and sevoflurane (MAC, oil:gas, blood:gas coefficient, metabolism)
65
what are the effects of isoflurane and sevoflurane on the CVS (2)
1. hypotension: CO maintained (except deep plane) and peripheral vascular resistance falls
2. no sensitization to catecholamines
66
what are the effects of isoflurane and sevoflurane on the resp system
1. depression: reduced rate
sevo causes less depression
67
what are the effects of desoflurane on CVS and resp rate
CVS: rapid increases in inspired concentration can increase heart rate and arterial BP (catecholamines)
resp: high inspired concentration can cause airway irritation
68
which agents have the highest onset
isoflurane \> sevoflurane \> desflurane
69
which agents can be used for mask induction
sevoflurane is the only one that has a pleasant odour
70
which agent has the least airway irritation
desflurane \> isoflurane \> sevoflurane
71
compare the authorization, potency, rate of change of depth, mask induction, metabolism and cost of isoflurane, sevoflurane, desflurane
72
what is nitrous oxide
weak anesthetic and weak analgesic
