8 - Sedatives Flashcards
1
Q
Why use premedication?
A
- Relieve anxiety and stress
- Smooth induction of anesthesia
- Smooth maintenance phase of anesthesia
- Smooth recovery of anesthesia
- Anesthetic sparing
- Provide analgesia
- Reduce muscle tone
2
Q
An ideal premedication should
A
- Relieve fear and anxiety
- Easily administered
- Reasonably quick onset of action and duration of action
- Antagonizable (reversible)
- Predictable and reliable
- Safe and effective in ALL species
- Produce minimal CV, respiratory and other side effects
- Some analgesia and muscle relaxation
- Possibly provide amnesia
3
Q
Pre-anesthetic medications
A
*sedative and analgesic component
- Phenothiazines (MAIN sedative)
- Butyrophenones
- Alpha2 agonists (MAIN sedative)
- (Benzodiazepines in some animals)
- Anticholinergics
- Opioids
4
Q
Phenothiazines, butyrophenones, alpha2 agonists
A
- Sedation to calm animal and reduce anxiety
- Anesthetic ‘sparing’ effect
5
Q
Anticholinergics
A
- Prevent undesirable side effects – bradycardia
- *at VMC don’t use it pre-emptively
6
Q
Opioids, alpha2 agonists, ketamine
A
- Provides analgesia (pre-emptively)
7
Q
Phenothiazines: actions
A
- Anti-adrenergic
- Antidopaminergic
- Anticholinergic
- Antihistamine
- Antiserotonergic
- Local anesthetic effects
- Anti-arrhythmic
- NO ANALGESIA
- Antithrombotic actions
8
Q
Phenothiazines: effects
A
- Sedation
- Hypotension
- Hypothermia
- Anti-emetic
- Anti-arrhythmic
9
Q
Phenothiazines: pharmacology
A
- 2 benzene rings that are linked by S and N atom
- Highly protein bound
- Lipophilic (cross BBB and placenta)
- Hepatic metabolism
10
Q
Phenothiazines: wide variety of actions
A
- *primarily depress parts of CNS which assist in control of homeostasis
o Vasomotor control
o Thermoregulation
o Hormonal balance
o Acid-base balance
o Emesis
11
Q
Phenothiazines: mechanism of action
A
- Mental calming effect: mediated by ANTIDOPAMINERGIC actions in CNS
o Post-synaptic DA receptor blockage in CNS=inhibition of dopamine release - Useful to calm, reduce anxiety, anesthetic sparing
- Overdose will cause catalepsy (increased extra-pyramidal signs)
12
Q
Phenothiazines: negative cardiovascular side effects
A
- HYPOTENSION through vascular smooth muscle alpha-1 receptor blockade
o Not reversible
o Duration is dose dependent (can last up to 8hrs)
o Supportive management (fluid therapy and pressure support)
o Avoid volume depleted animals or if hemorrhage is possible
13
Q
Phenothiazines: negative respiratory side effects
A
- Reduce sensitivity of respiratory center to CO2
- Slight reduction in RR
- Overall=no change in blood gas
14
Q
Phenothiazines: negative thermoregulatory side effects
A
- Hypothermia
o Due to disruption of thermoregulation and cutaneous vasodilation
15
Q
Phenothiazines: positive side effects
A
- Anti-emetic
- Anti-arrhythmic
- Anti-histamine
16
Q
Phenothiazines: anti-emetic
A
- Effect in central chemoreceptor trigger zone
- To be effective against opioids: administer 15-20mins prior
17
Q
Phenothiazines: anti-arrhythmic
A
- Increases concentration of epinephrine required to induce cardiac arrhythmias
18
Q
Acepromazine (Phenothiazines)
A
- Commonly used
- 30-40% sparing effect
- Mild sedation when used along, NO ANALGESIA
- Commonly combined with alpha2 agonists, opioids
- Used in cats, dogs, horses
- Can be used in seizure prone animals
- Solution is yellow
- Slow time to onset of effect
- Dose dependent: duration and severity of side effects (hypotension)
19
Q
Acepromazine (Phenothiazines): horses
A
- Can cause penile prolapse (rare)
- Don’t use in breeding males (stallions)
20
Q
Benzodiazepines
A
- Anticonvulsant
- Avoid using alone IV in dogs, cats, horses
o Excitement possible in young, healthy animals
o May become aggressive - Better combined with mu-opioids (good in really old, sick, obtunded dogs)
- Sedation when used for exotic animals
- Reduces amount of major anesthetic
- Muscle relaxation
- Retrograde amnesia
- NO analgesia
21
Q
Benzodiazepines: pharmacology
A
- Benzene rings fused to diazepine ring
- Well absorbed across mucous membrane
- Significant first-pass metabolism if administered orally=need to increase dose
- Highly protein bound
- Hepatic metabolism: oxidation and conjugation
22
Q
Benzodiazepines: mechanism of action
A
- Act on specific benzodiazepine binding sites: associated with GABAa receptors
o Enhances affinity for and/or action of GABA (inhibitory NT) - Depress activity in reticular activating system, by enhancing GABA actions=anxiolysis and sedation (dose dependant)
- Central GABA enhancing activity=anti-convulsant
- Act in SC=depressed internuncial NT=muscle relaxation
23
Q
GABA receptors and benzodiazepines
A
- When benzodiazepine binds=increase binding affinity for GABA NTs=opens Cl- channels=inhibitory effects
24
Q
Benzodiazepines: side effects
A
- Minimal CV
- Minimal respiratory
- *CNS depression (overdose=coma)
25
Q
Benzodiazepines: respiratory effects
A
- Can enhance respiratory depression caused by other anesthetic agents
o Due to reduced ventilatory response to CO2 and slight relaxation of intercostal muscles
26
Q
Diazepam
A
- Adheres to plastic syringes
- Sensitive to light degradation
- Propylene glycol carrier
- Active metabolites: Nordiazepam
- Crosses placenta
27
Q
Diazepam: propylene glycol carrier
A
- pH=6.8
- pain on IM injection
- unreliable absorption
28
Q
Diazepam: crosses placenta
A
- reaches fetus and remain in fetus
- *do NOT use for C-sections unless antagonist (flumazenil) is available
29
Q
Midazolam
A
- Contains imidazole ring
- Can be administered IM, intranasal, transmucosal
- 2-3x more potent than diazepam
- Inactive metabolites
- *popular in EXOTIC anesthesia: reliable sedation
30
Q
Midazolam: contains imidazole ring
A
- Acidic (pH<4): ring is open=water soluble
- If pH>4: ring is closed= highly lipophilic
31
Q
Flumazenil: benzodiazepine antagonist
A
- ANTAGONIST at benzodiazepine binding site on GABAa receptor
- No side effects
- Increases muscle tone to normal (IMPROVES ventilation)
- Useful for exotic animal anesthesia
- 30-60min duration IV, IM (need to continually monitor)
32
Q
Behavior Modifiers:
A
- Trazodone
- Gabapentin
- *most are on Gaba +/- Trazodone (not usually Trazodone alone)
33
Q
Trazodone
A
- Serotonin receptor antagonist and reuptake inhibitor (atypical antidepressant)
- Some alpha1 receptor blocking action (possible hypotension)
- Oral administration may be given before visit
- Similar to using acepromazine to decrease stress
- Can be combined with an opioid
34
Q
Gabapentin
A
- Inhibitory effect on voltage-gated calcium channels in neural tissue decreasing the release of glutamate within the CNS
- Oral administration may be given before visit
35
Q
Gabapentin is routinely used for
A
- Treatment of chronic pain
- Epilepsy
