Effects of inhalation anesthetic agents on response of horses to three hours of hypoxemia.
OBJECTIVE
To study the effects of inhalation anesthetic agents on the response of horses to 3 hours of hypoxemia.


METHODS
Controlled crossover study.


METHODS
Five healthy adult horses.


METHODS
Horses were anesthetized twice: once with halothane, and once with isoflurane in O2. Anesthetized horses were positioned in left lateral recumbency. Constant conditions for the study began at 2 hours of anesthesia. A constant agent dose of 1.2 minimum alveolar concentration, PaO2 of 50 +/- 5 mm of Hg, and PaCO2 of 45 +/- 5 mm of Hg were maintained for 3 hours. Circulatory measurements were made at 0.5, 1, 2, and 3 hours of hypoxemia (anesthesia hours 2.5, 3, 4, and 5). Blood was collected from horses for biochemical analyses before anesthesia, within a few minutes after standing, and at 1, 2, 4, and 7 days after anesthesia.


RESULTS
Cardiac index was greater (P = 0.018) during isoflurane than halothane anesthesia. Cardiac index remained constant during the 3 hours of hypoxemia during halothane anesthesia, whereas it decreased from the baseline during isoflurane anesthesia. Marginally nonsignificant P values for an agent difference were detected for arterial O2 content (P = 0.051), and oxygen delivery (P = 0.057). Serum activities of aspartate transaminase (P = 0.050) and sorbitol dehydrogenase (P = 0.017) were higher in halothane-anesthetized horses than in isoflurane-anesthetized horses. Circulatory function was better in hypoxemic horses anesthetized with isoflurane than with halothane. Isoflurane resulted in less muscular injury in hypoxemia horses than did halothane anesthesia. Halothane anesthesia and hypoxemia were associated with hepatic insult.


CONCLUSIONS
Isoflurane is better than halothane for hypoxemic horses.
Whitehair
K J
KJ
Veterinary Medical Teaching Hospital, Department of Surgical and Radiological Sciences, Davis, CA, USA.
Steffey
E P
EP
Woliner
M J
MJ
Willits
N H
NH
D000704:Analysis of Variance; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000818:Animals; D001219:Aspartate Aminotransferases / Q000097:blood; D001794:Blood Pressure / Q000187:drug effects; D002245:Carbon Dioxide / Q000097:blood; D002302:Cardiac Output / Q000187:drug effects; D018592:Cross-Over Studies; D006221:Halothane / Q000494:pharmacology*; D006339:Heart Rate / Q000187:drug effects; D006439:Hemodynamics / Q000187:drug effects*; D006736:Horses / Q000502:physiology*; D000860:Hypoxia; D007530:Isoflurane / Q000494:pharmacology*; D007064:L-Iditol 2-Dehydrogenase / Q000097:blood; D010100:Oxygen / Q000097:blood; D010101:Oxygen Consumption; D010313:Partial Pressure; D012119:Respiration / Q000187:drug effects*; D013997:Time Factors
D018685:Anesthetics, Inhalation; D002245:Carbon Dioxide; D007530:Isoflurane; D007064:L-Iditol 2-Dehydrogenase; D001219:Aspartate Aminotransferases; D010100:Oxygen; D006221:Halothane