Sedatives Flashcards
1
Q
Why use premedication?
A
- relieve anxiety and stress in the patient
- to smooth the induction of anesthesia
- to smooth the maintenance phase of anesthesia
- to smooth the recovery from anesthesia
- anesthetic sparing - reduce the dose of induction and maintenance anesthetic agents & thus reduce their side effects
- to provide analgesia
- to reduce muscle tone
2
Q
An ideal premedication SHOULD:
A
- relieve fear & anxiety
- be easily administered
- have reasonable quick onset of action & reasonable duration of action
- be antagonizable (reversible)
- be predictable (dose-dependent) & reliable
- be safe & effective in all species
- produce minimal cardiovascular, respiratory, & other side effects
- provide some analgesia & muscle relaxation
- possibly provide amnesia
3
Q
What are some pre-anesthetic medications (that can also be used for sedation only)?
A
- phenothiazines, butyrophenones, alpha2 agonists, (benzodiazepines in some animals): sedation to calm the animal & reduce anxiety; anesthetic ‘sparing’ effect
- anticholinergics: prevent undesirable side effects - bradycardia
- opioids, alpha2 agonists, ketamine: provide analgesia (pre-emptively)
4
Q
What are the actions of phenothiazines?
A
- anti-adrenergic (a1 blocker)
- antidopaminergic
- anticholinergic (muscarinic blocker)
- antihistaminic (H1 blocker)
- antiserotonergic (5-HT blocker)
- local anesthetic effects (ion channel blockade)
- anti-arrhythmic
- NO ANALGESIA
- antithrombotic actions
5
Q
What are the effects of phenothiazines?
A
- sedation
- hypotension
- hypothermia
- anti-emetic
- anti-arrhythmic
6
Q
What is the pharmacology of phenothiazines?
A
- contain two benzene rings that are linked by a sulphur and nitrogen atom
- highly protein bound (>90%)
- lipophilic - cross the BBB & placenta
- hepatic metabolism
- wide variety of actions - primarily depress parts of the CNS which assist in the control of homeostasis: vasomotor control, thermoregulation, hormonal balance, acid-base balance, emesis
7
Q
What is the mechanism of action of phenothiazines?
A
- mental calming effect - mediated by ANTIDOPAMINERGIC actions in the CNS: post-synaptic DA receptor blockade in the CNS -> inhibition of dopamine release
- useful to calm, seem to reduce anxiety, anesthetic sparing
- overdose of these drugs will cause catalepsy: increased extra-pyramidal signs
8
Q
What are the negative side effects of phenothiazines?
A
- CARDIOVASCULAR effects: HYPOTENSION through vascular smooth muscle alpha1 receptor blockade (not reversible; duration is dose-dependent but can last up to 8 hours; supportive management - fluid therapy & pressure support (ephedrine); avoid in volume depleted animals or if hemorrhage is possible)
- RESPIRATORY effects: reduces sensitivity of the respiratory center to CO2; slight reduction in respiratory rate; overall - no change in blood gas
- THERMOREGULATORY effects: hypothermia can occur due to disruption of thermoregulation & cutaneous vasodilation
9
Q
What are the positive side effects of phenothiazines?
A
- ANTI-EMETIC: effect in the central chemoreceptor trigger zone; to be effective against opioids - administer 15-20 mins prior
- ANTI-ARRHYTHMIC: increases the concentration of epinephrine required to induce cardiac arrhythmias
- ANTI-HISTAMINE: contraindicated prior to allergy testing/skin biopsies
10
Q
What is acepromazine (phenothiazine)?
A
- commonly used in vet med - calming effect
- 30-40% anesthetic sparing effect
- mild sedation when used alone
- NO ANALGESIA
- commonly combined w/ alpha2 agonists or opioids
- used in Fe, Ca, Eq (HAVE BEEN RARE CASES OF PENILE PROLAPSE WITH ACEPROMAZINE - SO DONT USED IT IN BREEDING STALLIONS), rarely used in Ru & exotics
- can be used in seizure prone animals
- can also be used for controlling emergence delirium during recovery from anesthesia
- solution is yellow in colour
- slow time to onset of effects (even after IV administration)
- dose dependent: duration; severity of side effects - HYPOTENSION
11
Q
What are benzodiazepines?
A
- ANTICONVULSANTS
- AVOID using ALONE IV in Ca, Fe, Eq: EXCITEMENT is possible in young, healthy animals; may become AGGRESSIVE
- better if combined w/ mu-opioids (IV or IM): combination is good in SICK, OBTUNDED dogs
- sedation when used for exotic animals
- reduces amount of major anesthetic (anesthetic sparing)
- muscle relaxation
- retrograde amnesia
- NO ANALGESIA
12
Q
what is the pharmacology of benzodiazepines?
A
- consist of benzene rings fused to a diazepine ring
- well absorbed across mucous membranes
- significant first-pass metabolism if administered orally - need to increase dose
- highly protein bound (>95%)
- hepatic metabolism - oxidation and conjugation
13
Q
What is the mechanism of action of benzodiazepines?
A
- act on specific benzodiazepine binding sites - which are associated w/ GABA”A” receptors: enhance the affinity for &/or action of GABA (inhibitory NT)
- depresses activity in reticular activating system, by enhancing GABA actions -> ANXIOLYSIS & SEDATION (dose dependent; SEDATION IS UNRELIABLE IN SOME ANIMALS - CAN CAUSE EXCITEMENT)
- central GABA-enhancing activity -> ANTI-CONVULSANT effect
- act in the spinal cord - depress internuncial neurotransmission -> MUSCLE RELAXATION
14
Q
What are the side effects of benzodiazepines?
A
- CARDIOVASCULAR effects: minimal
- RESPIRATORY effects: minimal; can enhance the respiratory depression caused by other anesthetic agents - due to reduced ventilatory response to CO2 & slight relaxation of intercostal muscles
- CNS depression: overdose causes coma
15
Q
What is diazepam?
A
- adheres to plastic syringes (takes up to 12 hours)
- sensitive to light degradation
- propylene glycol carrier (pH 6.8): painful on IM injection & unreliable absorption
- active metabolites - Nordiazepam
- crosses placenta, reaches fetus, & remains in fetus: DO NOT use for c-sections unless antagonist (Flumazenil) is available
