The effect of nitrous oxide on halothane, isoflurane and sevoflurane requirements in ventilated dogs undergoing ovariohysterectomy.
OBJECTIVE
To examine the effect of 64% nitrous oxide (N2O) on halothane (HAL), isoflurane (ISO) or sevoflurane (SEV) requirements in dogs undergoing ovariohysterectomy.


METHODS
Prospective, randomized, clinical trial.


METHODS
Ninety, healthy dogs of (mean +/- SD) body weight 21.2 +/- 10.0 kg and age 17.8 +/- 22.8 months.


METHODS
After premedication with acepromazine, hydromorphone and glycopyrrolate, anesthesia was induced with thiopental administered to effect. Dogs received one of six inhalant protocols (n = 15 group): HAL; HAL/N2O; ISO; ISO/N2O; SEV; or SEV/N2O. End-tidal CO2 was maintained at 40 +/- 2 mmHg with intermittent positive pressure ventilation (IPPV). Body temperature, heart rate, indirect systemic arterial blood pressures, inspired and end-tidal CO2, volatile agent, N2O and O2 were recorded every 5 minutes. The vaporizer setting was decreased in 0.25-0.5% decrements to elicit a palpebral reflex, and this level maintained. Statistical analysis included two-way anova for repeated measures with Bonferroni's correction factor and statistical significance assumed when p < 0.05. Percentage reduction in end-tidal volatile agent was calculated at 60 minutes after starting study.


RESULTS
End-tidal HAL, ISO and SEV decreased when N2O was administered. Percentage reduction: HAL (12.4%); ISO (37.1%) and SEV (21.4%). Diastolic, mean and systolic blood pressures increased in ISO/N2O compared with ISO. Heart rate increased in ISO/N2O and SEV/N2O compared with ISO and SEV, respectively. Systolic, mean and diastolic blood pressures increased in SEV compared with HAL and ISO. Systolic, mean, diastolic blood pressures and heart rate increased in SEV/N2O and ISO/N2O compared with HAL/N2O.


CONCLUSIONS
N2O reduces HAL, ISO and SEV requirements in dogs undergoing ovariohysterectomy. Cardiovascular stimulation occurred when N2O was used with ISO, less so with SEV and not with HAL
Duke
T
T
Department Small Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, SK, Canada. tanya.duke@usask.ca
Caulkett
N A
NA
Tataryn
J M
JM
D000769:Anesthesia, Inhalation / Q000662:veterinary*; D018685:Anesthetics, Inhalation / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D001784:Blood Gas Analysis / Q000662:veterinary; D004285:Dogs / Q000502:physiology*; D004359:Drug Therapy, Combination; D005260:Female; D006221:Halothane / Q000008:administration & dosage / Q000494:pharmacology; D007044:Hysterectomy / Q000662:veterinary; D007530:Isoflurane / Q000008:administration & dosage / Q000494:pharmacology; D008168:Lung / Q000187:drug effects*; D008738:Methyl Ethers / Q000008:administration & dosage / Q000494:pharmacology; D009609:Nitrous Oxide / Q000008:administration & dosage / Q000494:pharmacology*; D011446:Prospective Studies; D012119:Respiration / Q000187:drug effects; D000077149:Sevoflurane; D016896:Treatment Outcome
D018685:Anesthetics, Inhalation; D008738:Methyl Ethers; D000077149:Sevoflurane; D007530:Isoflurane; D009609:Nitrous Oxide; D006221:Halothane