Inhalants Flashcards
What three inhalants are considered the “modern” anesthetic agents?
1) Sevoflurane
2) Desflurane
3) Isoflurane
Do we know the molecular mechanism of action for inhalants?
not really, but we know some of the receptors they act on (GABAa, NMDA, glycine)
Is inhalant anesthesia immobility brain or spinally mediated?
spinal
gas
agent which exists in gaseous form at room temp and sea level
vapor
agent which exists in liquid form at room temp and sea level
Which undergoes a phase change - gas or vapor?
vapor
What is the only inhalant anesthetic to NOT be considered a vapor?
nitrous oxide (N2O)
blood:gas partition coefficient
ratio of the concentration of anesthetic in the blood vs. anesthetic in the alveoli
solubility
measure of how soluble an anesthetic is in blood
Are partition coefficient and solubility synonymous?
yes
relationship between solubility and time to induce anesthesia
higher solubility = longer time to induce anesthesia
Benefits of low solubility/blood:gas coefficient (3)
1) Faster induction
2) More control over depth
3) Faster recovery
Minimum Alveolar Concentration (MAC)
MAC at 1atm that results in immobility in 50% of patients (the dose that keeps our patients under anesthesia)
Relationship between solubility and MAC
Low solubility = high MAC
Is MAC determined in sick or healthy animals?
healthy, with no other drugs!
keep this in mind because some conditions/drugs may affect (reduce) the MAC
Isoflurane MAC in Cat & Dog & Horse
Cat = 1.63
Dog = 1.30
Horse = 1.31
Sevoflurane MAC in Cat & Dog & Horse
Cat = 2.58
Dog = 2.36
Horse = 2.31
Desflurane MAC in Cat & Dog & Horse
Cat = 9.79
Dog = 7.20
Horse = 8.06
Vessel Reach Group (VRG)
organs which are highly vascularized (brain, lungs, heart, kidneys)
What two tissues have the highest partition coefficients (therefore will suck up a lot of the anesthesia)?
muscle and fat
relationship between cardiac output and induction time
higher cardiac output = longer induction time
clearance
elimination of anesthetic from the CNS
Fluoride-Associated Nephrotoxicity
previously seen with inhalant anesthetics but risk is minimal with modern inhalants
effect of inhalants on cerebral blood flow
INCREASE (dose-dependent)
Do inhalants cause vasoconstriction or vasodilation?
vasodilation
effect of inhalants on intracranial pressure (ICP)
INCREASE
apneic index
1.5-3 times the MAC
indicates need for mechanical ventilation
Do inhalants enhance or depress the respiratory system?
depress
effect of inhalants on PaCO2
INCREASE
Are inhalants bronchoconstrictors or bronchodilators?
bronchodilators!
effect of inhalants on cardiac output
DECREASE (dose-dependent)
due to decrease in stroke volume for decreased contractility
effect of inhalants on arterial blood pressure
DECREASE (dose-dependent)
Can inhalants cause renal effects?
YES but it is LIMITED to the time of anesthesia and is reversible
Hepatic Effects of Inhalants
minimal (total flow maintained, some portal venous decrease)
Malignant hyperthermia primarily affects what species?
pigs (halothane is the worst offender but all inhalants do it)
Do inhalants cross the placenta?
yes
Are inhalants safe to use in pregnant animals?
yes, but MAC should stay under 1.5 (dose dependent decreases in contractility and blood flow do occur starting at 0.5)
inhalants exhaled by newborn upon birth
