Effects of nitrous oxide on mask induction of anesthesia with sevoflurane or isoflurane in dogs.
OBJECTIVE
To determine the effects of nitrous oxide (N2O) on the speed and quality of mask induction with sevoflurane or isoflurane in dogs.


METHODS
7 healthy Beagles.


METHODS
Anesthesia was induced with sevoflurane or isoflurane delivered in 100% oxygen or in a 2:1 mixture of N2O and oxygen via a face mask. Each dog received all treatments with at least 1 week between treatments. Initial vaporizer settings were 0.8% for sevoflurane and 0.5% for isoflurane (0.4 times the minimum alveolar concentration [MAC]). Vaporizer settings were increased by 0.4 MAC at 15-second intervals until settings were 4.8% for sevoflurane and 3.0% for isoflurane (2.4 MAC). Times to onset and cessation of involuntary movements, loss of the palpebral reflex, negative response to tail-clamp stimulation, and endotracheal intubation were recorded, and cardiopulmonary variables were measured.


RESULTS
Administration of sevoflurane resulted in a more rapid induction, compared with isoflurane. However, N2O had no effect on induction time for either agent. Heart rate, mean arterial blood pressure, cardiac output, and respiratory rate significantly increased and tidal volume significantly decreased from baseline values immediately after onset of induction in all groups. Again, concomitant administration of N2O had no effect on cardiopulmonary variables.


CONCLUSIONS
Administration of N2O did not improve the rate or quality of mask induction with sevoflurane or isoflurane. The benefits provided by N2O attributable to concentrating and second gas effects appear minimal in healthy dogs when low solubility inhalation agents such as isoflurane and sevoflurane are used for mask induction.
Mutoh
T
T
Laboratory of Veterinary Surgery, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Japan.
Nishimura
R
R
Sasaki
N
N
D000769:Anesthesia, Inhalation / Q000379:methods / Q000662:veterinary*; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002302:Cardiac Output / Q000187:drug effects; D004285:Dogs / Q000378:metabolism* / Q000502:physiology; D004347:Drug Interactions; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D007530:Isoflurane / Q000494:pharmacology*; D008297:Male; D008397:Masks / Q000662:veterinary*; D008738:Methyl Ethers / Q000494:pharmacology*; D009609:Nitrous Oxide / Q000494:pharmacology*; D012119:Respiration / Q000187:drug effects; D000077149:Sevoflurane
D018685:Anesthetics, Inhalation; D008738:Methyl Ethers; D000077149:Sevoflurane; D007530:Isoflurane; D009609:Nitrous Oxide