small mammals 3 - Sedation, Anesthesia, and Analgesia Flashcards
why do small mammals have increased anesthetic risks
- Low body mass – high surface area to volume ratio – high metabolic rate
- Allometric scaling of dosages (higher) and/or frequency (shorter)
- High oxygen and glucose demands → low tolerance
to hypoxia (irreversible CNS injury within 30 seconds of respiratory arrest) - High respiratory rate → rapid uptake and excretion of volatile anesthetics
- Rapid heat loss (and thermoregulatory suppression) → hypothermia – impairs CV, coagulation, metabolism, and recovery
- Stress on induction → catecholamines (dopamine, norepinephrine, epinephrine) → vasoconstriction, hypertension, tachycardia, elevated blood glucose, and dysrhythmias at high circulating levels
- More difficult to catheterize
- Breath-holding
- More difficult to intubate
- Narrow therapeutic index
- Perceived increased sensitivity
to respiratory depression of drugs - Respiratory disease is common, especially in rabbits and rats
pre-op stabilization - what should we do / examine aside from the regular
- Reduce stress – acclimate, no predators, provide hide/shelter, dark, quiet, bonded mate
- Temperature
- Fluid deficits –further vasodilation by induction agents → hypotension
- Anemia < 20% - unable to compensate for decreased oxygen delivery
- Pre-oxygenation
pre-op oxygenation purose? how to do it?
- Creates oxygen reservoir
> Hypoventilation
> Difficult to intubate - 1-5minutes
- Oxygen-enriched incubator or induction chamber
- Flow-by or mask
should small mammals fast before op? when should we vs shouldnt we, why?
No
* Rabbits and rodents cannot vomit
* Causes hypoglycemia
* Causes gastric stasis
* Little decrease in gastrointestinal volume
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Yes
* Ferrets can vomit
* Reduces food in oropharynx
* Blind intubation
* Dental
Benzodiazepine mechanism? which do we use for small mammals?
- Enhance the inhibitory function of GABA receptors → depresses
the CNS – varying sedative, hypnotic, anxiolytic, anticonvulsant, muscle relaxant, and amnesic properties - Midazolam – water soluble, IV/IM/SC
Flumazenil - what is this
reversal for benzodiazepine
> competitive inhibition of benzodiazepine receptors, slow IV/IM +/- SC, short-acting (repeat)
opioids we use in small mammals? what receptors do they act on? reversal?
- Hydromorphone, fentanyl – full μ
- Buprenorphine(SR) – partial μ
- Butorphanol – μ antagonist and κ agonist
- Reversal: Naloxone
which opioids are the best analgesics?
Full μ agonists (e.g., morphine, hydromorphone, fentanyl, remifentanil, alfentanil, oxymorphone, and methadone) produce the most profound analgesic effects.
buprenorphine properties
The partial μ agonist buprenorphine produces a clinically useful analgesic effect that is generally less profound than a full μ agonist and as such is only expected to be useful for mild to moderate pain. However, clinical studies suggest that buprenorphine may be as effective as full opioid agonists (e.g., morphine) for some types of pain with fewer adverse effects.
butorphanol properties
Butorphanol is generally considered to be a μ antagonist and κ agonist with relatively modest analgesic effects. However, some reports show that butorphanol may produce more profound analgesic effects than buprenorphine in certain species.
use of alpha2 agonists for small mammals? side effects? which one do we use a lot?
- Sedation, analgesia, muscle relaxation
- Side effects – respiratory depression, increased systemic vascular resistance, bradycardia
- Dexmedetomidine
Alpha-2 Antagonist
Atipamezole
Dissociative anesthetic drugs - how they work, what they do, side effects? what drug we use a lot?
- Act on NMDA, opioid, monoaminergic, and muscarinic receptors
- Cataleptic state
- Sympathomimetic – increased heart rate, contractility
- Side effects – muscle rigidity, eyes open
- Ketamine
Alfaxalone - how it works, side effects
- Neuroactive steroid
- Binding to GABA receptors
- Side effects – respiratory depression IV
Propofol - how it works, side effects
- GABA and NMDA receptors
- IV/IO
- Side effects – respiratory depression
