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ANESTHESIA > 8 - Sedatives > Flashcards

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
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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
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3
Q

Pre-anesthetic medications

A

*sedative and analgesic component
- Phenothiazines (MAIN sedative)
- Butyrophenones
- Alpha2 agonists (MAIN sedative)
- (Benzodiazepines in some animals)
- Anticholinergics
- Opioids

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4
Q

Phenothiazines, butyrophenones, alpha2 agonists

A
  • Sedation to calm animal and reduce anxiety
  • Anesthetic ‘sparing’ effect
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5
Q

Anticholinergics

A
  • Prevent undesirable side effects – bradycardia
  • *at VMC don’t use it pre-emptively
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6
Q

Opioids, alpha2 agonists, ketamine

A
  • Provides analgesia (pre-emptively)
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7
Q

Phenothiazines: actions

A
  • Anti-adrenergic
  • Antidopaminergic
  • Anticholinergic
  • Antihistamine
  • Antiserotonergic
  • Local anesthetic effects
  • Anti-arrhythmic
  • NO ANALGESIA
  • Antithrombotic actions
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8
Q

Phenothiazines: effects

A
  • Sedation
  • Hypotension
  • Hypothermia
  • Anti-emetic
  • Anti-arrhythmic
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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
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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
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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)
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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
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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
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14
Q

Phenothiazines: negative thermoregulatory side effects

A
  • Hypothermia
    o Due to disruption of thermoregulation and cutaneous vasodilation
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15
Q

Phenothiazines: positive side effects

A
  • Anti-emetic
  • Anti-arrhythmic
  • Anti-histamine
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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

ANESTHESIA (27 decks)

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