EFFECTS OF INHALATION ANESTHETIC AGENTS ON RESPONSE OF HORSES TO 3 HOURS OF HYPOXEMIA

Objective-To study the effects of inhalation anesthetic agents on the response of horses to 3 hours of hypoxemia. Design-Controlled crossove r study. Animals-Five healthy adult horses. Procedure-Horses were anes thetized twice: once with halothane, and once with isoflurane in O-2. Anesthetized horses were positioned in left lateral recumbency. Consta nt conditions for the study began at 2 hours of anesthesia. A constant agent dose of 1.2 minimum alveolar concentration, Pa-o2 of 50 +/- 5 m m of Hg, and Pa-co2 of 45 +/- 5 mm of Hg were maintained for 3 hours. Circulatory measurements were made at 0.5, 1, 2, and 3 hours of hypoxe mia (anesthesia hours 2.5, 3, 4, and 5). Blood was collected from hors es for biochemical analyses before anesthesia, within a few minutes af ter standing, and at 1, 2, 4, and 7 days after anesthesia. Results-Car diac index was greater (P = 0.018) during isoflurane than halothane an esthesia. Cardiac index remained constant during the 3 hours of hypoxe mia during halothane anesthesia, whereas it decreased from the baselin e during isoflurane anesthesia. Marginally nonsignificant P values for an agent difference were detected for arterial O-2 content (P = 0.051 ), and oxygen delivery (P = 0.057). Serum activities of aspartate tran saminase (P = 0.050) and sorbitol dehydrogenase (P = 0.017) were highe r in halothane-anesthetized horses than in isoflurane-anesthetized hor ses. Circulatory function was better in hypoxemic horses anesthetized with isoflurane than with halothane. Isoflurane resulted in less muscu lar injury in hypoxemia horses than did halothane anesthesia. Halothan e anesthesia and hypoxemia were associated with hepatic insult. Conclu sion-Isoflurane is better than halothane for hypoxemic horses.