11/12: Induction Agents & Techniques Flashcards
1
Q
What is stage I of anesthetic depth?
A
Stage of voluntary movement; from initial admin of drugs to loss of consciousness
2
Q
What is stage II of anesthetic depth?
A
Stage of delirium and involuntary movement; disinhibition; react to stimuli, struggle, vocalize
3
Q
T/F: Intubation should be attempted at stage II of anesthetic depth
A
False;
There is risk of vomiting/regurgitation
4
Q
What is stage III of anesthetic depth?
A
Progressive loss of reflexes/muscle tone (light, medium, deep)
5
Q
Where are eyes located in the light plane of stage III?
A
6
Q
Where are eyes located in the medium plane of stage III?
A
7
Q
Where are eyes located in the deep plane of stage III?
A
8
Q
What is a good way to check if an animal is too light or too deep?
A
Check palpebral reflexes
9
Q
Which is the most important stage and where do you want your patient to be?
A
Stage III;
Want to be somewhere between plane 1 and plane 2
10
Q
What is stage IV of anesthetic depth?
A
Extreme CNS depression;
Pulses weak/not palpable, resp may cease;
eyes central, pupils dilated
11
Q
What are the 5 criteria of general anesthesia?
A
- Analgesia (loss of response to pain)
- Amnesia (loss of memory)
- Immobility (loss of motor reflexes)
- Hypnosis (unconsciousness)
- Paralysis (skeletal m relaxation and normal m relaxation)
12
Q
What is pharmacokinetics?
A
What the body does to the drugs
13
Q
What is pharmacodynamics?
A
What drugs do to the body
14
Q
Why does it take some time for a drug to circulate to the brain after it is given?
A
Depends on circulation time and equilibrium time;
Has to cross BBB and interstitium
15
Q
What is the % CO to the brain?
A
14%
16
Q
What is the % CO to the kidney?
A
23%
17
Q
What is the % CO to the liver?
A
5.8%
18
Q
What is the % CO to the muscles?
A
16%
19
Q
What is the % CO to the skin?
A
5%
20
Q
What is the % CO to the fat?
A
2%
21
Q
Why does drug [] decrease over time (after initial increase)?
A
Because it is distributed to the fat and muscle and away from the brain
22
Q
What is the ideal administration rate?
A
Not too fast, not too slow
23
Q
What can happen if a drug is administered too fast?
A
Overdose
24
Q
What can happen if a drug is administered too slowly?
A
Stage 2 or not anesthetized at all
25
Concentration = solute/solution = \_\_\_\_\_/\_\_\_\_\_
Drug (X) / Volume of distribution (Vd)
26
Why is the apparent volume of a drug not the actual volume?
Due to distribution
27
What drug characteristics influence distribution?
Lipophilicity, protein binding, tissue binding, charge, pKa, size
28
What patient characteristics influence distribution?
Age, breed, body composition, pH, plasma protein, tissue inflammation
29
Larger Vd = _____ \_\_\_\_\_
longer duration
30
Which of these drugs have the largest Vd?
C \> A \> B
31
How do you calculate the loading dose?
C x Vd
32
Calculate the loading dose of propofol in dogs:
Vd = 0.78 L/kg, Induction [] = 8 µg/mL
Dose = C x Vd
Dose = 8 µg/mL x 0.78 L/kg
Dose = 8 mg/L x 0.78 L/kg
Dose = **6.14 mg/kg**
33
What does this graph represent?
First-order kinetics
34
What does this graph represent?
Zero-order kinetics
35
What is plasma/blood clearance?
Volume of a totally cleared substance per unit of time
36
What is the equation for clearance?
Clearance = *k* x Vd
| (*k* = elimination constant)
37
What are the phases of half life?
Distribution and elimination
38
What is the equation for half life?
t1/2 = 0.693/*K*
39
How is infusion rate calculated?
C (ss) x *K* x Vs (ss)
= C (ss) x Cl
40
Calculate infusion rate of propofol in dogs:
Vd (ss) = 4.5 L/kg, Cl = 54 ml/kg/min, t1/2 = 57 minutes, *K* = 0.012 minute-1, maint [] = 4 µg/ml
IR = C (ss) Cl
IR = 4 µg/ml x 54 ml/kg/min
IR = **208 µg/kg/min**
41
What does one vial of propofol contain?
1% propofol, soybean oil, egg phasphatide, glycerol, NaOH
42
Propofol is ____ at room temp and is not tissue \_\_\_\_.
stable, irritating
43
How long after opening does propofol have to be discarded and why?
6 hours - adjuvant promotes bacterial growth
44
What does Propofol 28 contain and why is it problematic?
Benzyl alcohol - toxic to cats;
Can cause hemolysis, may be able to use for a single injection only
45
What is the shelf life of propofol 28?
28 days from opening
46
Propofol 28 is bacterio\_\_\_\_\_.
static
47
What is unique about fospropofol?
It is transparent due to not having a lipid carrier
48
What is the onset and duration of fospropofol compared to Propofol 28?
Longer
49
What is fospropofol used for?
Long-term sedation in humans; studied extensively in vet med
50
What is the onset and duration of propofol?
Onset rapid = ~30 seconds
Duration short due to redistribution
51
Where is propofol metabolized and excreted?
Metab in liver, excreted thru kidney
52
Propofol causes _____ recovery in cats.
prolonged
53
What is the MOA of propofol?
Acts on GABAA receptor --\> open Cl channel --\> hyperpolarization;
Cell cannot mount action potential so brain becomes very depressed
54
Other than propofol, what other 2 drugs have major potentiation at GABAA receptors?
Barbiturates, etomidate
55
What is the relationship of ketamine with GABAA receptors and NMDA?
GABAA = minor potentiation
## Footnote
**NMDA = major inhibition**
56
Propofol _____ brain oxygen demand (CMRO2) and brain blood flow (CBF), hence **\_\_\_\_\_ intracranial pressure (ICP)**.
decreases, **decreasing**
57
What is the concern with propofol and hypotension?
Prop can cause hypotension, so cerebral perfusion might be decreased;
Need to be careful that patient doesn't become ischemic
58
What is dystonia?
NOT SEIZURE
Paddling, muscle twitching, opistothonus;
Common during induction and recovery with propofol, multiple potential mechanisms
59
How can you differentiate between dystonia and a seizure?
Give something to treat a seizure and if symptoms don't stop then it is likely dystonia
60
CV depression due to propofol is _____ dependent.
dose
61
Other than CV depression, what other CV effects can propofol have?
Vasodilation (direct or indirect), decreased contractility
62
What effects does propofol have on the respiratory system?
1. Dose-dependent depression
2. Dose, speed of injection, dependent apnea
63
What are other side effects that propofol can cause?
1. Oxidative stress to RBC in cats (from phenol structure)
2. +/- pancreatitis
1. Prolonged infusion in humans
2. Dog = increase triglyceride only
64
What are advantages to co-induction with propofol?
Improve quality, decrease adverse effects
65
What are disadvantages to co-induction with propofol?
Potential excitement, extra steps, cost, skill/experience
66
What drugs can be used as co-induction agents with propofol?
BDZ, ketamine, lidocaine, opioids (fentanyl)
67
Diazepam is _____ potent and _____ lipophilic than propofol, resulting in _____ "time lag"
less, less, more
68
When should diazepam be administered if given with propofol?
Prior to propofol
69
Midazolam is _____ potent and _____ lipophilic than propofol, resulting in _____ "time lag"
more, more, less
70
When should midazolam be administered if given with propofol?
Immediately prior to or after propofol
71
Co-induction of propofol with BDZ does not help with \_\_\_\_\_.
BP
72
What are the advantages of Total IV Anesthesia (TIVA)?
Potential benefits for intracranial hypertension patients, less hypotension and use of vasopressor.
73
What are the disadvantages of Total IV Anesthesia (TIVA)?
Cost, accumulation?
74
What is alfaxalone?
Basically a transparent propofol that can be given IM
75
What are Althesin/Saffan?
Steroid anesthetics alfaxalone + alphadolone in cremophor EL;
Alfaxalone may provide hypnosis, alphadolone may provide analgesia
76
What was a big disadvantage of Athesin/Saffan?
Reactions to cremophor EL led to withdrawal (swollen paws, ears, larynx, pulm edema)
77
What drug are the pharmacokinetics of alfaxalone similar to?
Propofol
78
What breed has a difference in alfaxalone metabolism?
Greyhounds
79
What does alfaxalone use cause animals to be sensitive to?
SOUND! and touch
80
What CV effect seems to be better reserved with alfaxalone than propofol in dogs?
baroreflex
81
Alfaxalone has a _____ Apgar score than propofol but _____ difference in mortality in c-section.
better, no
82
Recovery quality with alfaxalone is _____ or _____ than propofol.
similar, slightly worse
83
What are the physiochemical characteristics of Etomidate?
1. Water insoluble
2. 35% propylene glycol
3. Lipid emulsion
4. New formulation with cyclodextrin
84
In humans, where is Etomidate primarily metabolized?
liver
85
How is Etomidate excreted in humans?
85% by kidney, rest through bile and feces
86
What is the method of action of Etomidate?
Acts on GABAA
87
What unwanted thing can Etomidate cause, esp if used in a septic patient?
Iatrogenic Addison's (low steroid #s)
88
Etomidate _____ CMRO2, CBF, and ICP.
decreases
89
What about CPP (cerebral perfusion pressure) with Etomidate is opposite of propofol?
It is maintained or increased --\> net increase in oxygen supply to demand ratio
90
What effect can Etomidate have that is associated with the brainstem or deep cerebral acitivity? What is done to mitigate this?
Myoclonus;
Commonly combined with midazolam
91
What effect does Etomidate have on the cardiopulmonary system?
Minimal
92
What is the effect of Etomidate on baroreflex?
It is well-maintained
93
What effect does Etomidate have on the endocrine system?
Dose-dependent, temporary suppression
94
What other side effects does Etomidate have?
Nausea/vomiting, pain on injection, excitement
95
What type of solution is ketamine prepared in?
Slightly acidic (pH 3.5-5.5)
96
What is ketamine's relationship with water?
Freely water-soluble
97
What happens if you give ketamine orally?
Animal will foam a lot because it is bitter
98
What is the onset and duration of ketamine?
Rapid onset (but slower than other injectables) = 45-60 seconds
Short duration (redistribution)
99
How is ketamine eliminated?
Ketamine (active) --\> norketamine (active) --\> water soluble inactive metabolites
100
What type of drug is Ketamine?
NMDA receptor non-competitive antagonist
101
T/F: Ketamine is a monoaminergic --\> antinociception
True
102
What "state" does ketamine cause and what does this mean?
Cataleptic state - dissociation of limbic and thalamocortical system;
Eyes open with slow nystagmic gaze and pupillary dilation, varying degrees of hypertonus;
Salivation, lacrimation common
103
What reflexes stay intact with ketamine administration?
Corneal and light reflexes
104
How is recovery from ketamine without proper sedation?
rough
105
What effect does ketamine have (bc it is an NMDA R antag) that propofol and like drugs do not?
analgesia
106
What can ketamine cause in the CNS and what is used to mitigate it?
1. Intracranial hypertension - can use mechanical ventilation and combo with BDZ
2. Can also cause seizures
107
What cardio effects can ketamine have?
1. Increased HR, BP, CO
2. Direct myocardial depression (increased symp tone mitigates this)
108
What effect does ketamine have on respiration?
Insignificant depression, but higher dose can cause "apneustic" pattern
109
What is a apneustic pattern?
Prolonged inspiratory pause - inhale, hold breath, exhale
110
Ketamine is a muscarinic _____ and can cause _____ and \_\_\_\_\_.
antagonist, bronchodilation, airway secretion/hypersalivation
111
What effect does ketamine have on the eyes?
Increases IO pressure due to extraocular muscle contraction
112
Where might we use Telazol?
In wildlife and shelter medicine
113
Which component of telazol is metabolized faster by dogs and horses? What does this lead to?
Zolazepam --\> rough recovery
114
Which component of telazol is metabolized faster by cats and pigs? What does this lead to?
Tiletamine --\> smooth recovery
115
What is the induction protocol for critically ill patients?
Opioid + BDZ
(GDV, septic/hemoabd, severe heart disease)
116
What would be the only indication for using an inhalant anesthetic for induction? What is the exception?
Patient is too fractious or wild to be handled for an IM injection (RARE);
Exception = small exotic and avian spp where IV access is not possible
117
What are disadvantages of using an inhalant anesthetic as an induction agent?
1. Slower and stressful induction time (increased symp tone, harder to induce, prone to arrhythmia)
2. Patient goes thru all stages of anesthesia (risk of injury - thrash, flail, vocalize, urinate, defecate)
3. Waste gas pollution and exposure
