Cardiorespiratory effects of low-flow and closed circuit inhalation anesthesia, using sevoflurane delivered with an in-circuit vaporizer and concentrations of compound A.
OBJECTIVE
To determine the concentrations of sevoflurane and compound A (a degradation product of sevoflurane) in the anesthetic circuit when sevoflurane was delivered with an in-circuit vaporizer, and to determine the cardiorespiratory effects of sevoflurane in dogs.


METHODS
6 mixed-breed dogs.


METHODS
In-circuit vaporizers were connected to the inspiratory limb of a circle rebreathing system connected to a ventilator. A reservoir bag was attached to the Y-piece connector to act as an artificial lung, and sevoflurane concentrations in the anesthetic circuit were measured at vaporizer settings of 1, 3, 5, 7, and 10 and oxygen flow rates of 250 and 500 ml/min. Cardiorespiratory effects of sevoflurane were determined in dogs while they were breathing spontaneously, during controlled ventilation, and during closed circuit anesthesia. Concentrations of compound A were determined by means of gas chromatography with flame ionization.


RESULTS
The concentration of sevoflurane in the anesthetic circuit increased with vaporizer setting and time. For oxygen flow rates of 250 and 500 ml/min, vaporizer settings between 5 and 7 and between 7 and 10, respectively, produced sevoflurane concentrations closest to values reported to produce surgical anesthesia in dogs. Significant differences were not observed in cardiorespiratory variables with time or among anesthetic conditions. Concentrations of compound A in the anesthetic circuit were less than values reported to produce renal toxicoses and death in rats.


CONCLUSIONS
Results suggested that sevoflurane can be administered to nonsurgically stimulated dogs, using an in-circuit vaporizer and low (< 15 ml/kg/min) oxygen flow rates, without causing significant cardiorespiratory depression or clinically important concentrations of compound A.
Muir
W W
WW
Department of Veterinary Clinical Sciences, Ohio State University, Columbus 43210, USA.
Gadawski
J
J
D000764:Anesthesia, Closed-Circuit / Q000662:veterinary*; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000818:Animals; D004285:Dogs; D004987:Ethers / Q000032:analysis*; D006439:Hemodynamics / Q000187:drug effects*; D006845:Hydrocarbons, Fluorinated / Q000032:analysis*; D008738:Methyl Ethers / Q000494:pharmacology*; D009330:Nebulizers and Vaporizers / Q000662:veterinary*; D012121:Respiration, Artificial / Q000662:veterinary; D000077149:Sevoflurane
D018685:Anesthetics, Inhalation; D004987:Ethers; D006845:Hydrocarbons, Fluorinated; D008738:Methyl Ethers; D000077149:Sevoflurane; C078742:fluoromethyl 2,2-difluoro-1-(trifluoromethyl)vinyl ether