Cardiorespiratory effects of sevoflurane, isoflurane, and halothane anesthesia in horses

Objective-To determine and compare cardiorespiratory and recovery effects of sevoflurane, isoflurane, and halothane in horses. Animals-8 clinically normal horses (4 mares, 4 geldings), 5 to 12 years old. Procedure-Inhalation anesthesia was maintained for 90 minutes with sevoflurane, isoflurane, or halothane. Anesthesia depth was maintained at 1.5 minimum alveolar concentration of halothane, isoflurane, and sevoflurane, then was reduced at 30 and 60 minutes. A surgical plane of anesthesia was reinduced by administration of ketamine or thiopental or by increasing the fractional inspired concentration of sevoflurane. Cardiovascular and pulmonary variables were recorded and compared among inhalation anesthetics. Recovery was monitored, and subjective assessment of recovery quality was performed. Results-Hemodynamic and pulmonary indices during sevoflurane anesthesia were similar to those of isoflurane. Cardiac output and systemic arterial pressure decreased less during sevoflurane and isoflurane anesthesia than during halothane anesthesia. After 90 minutes, cardiac output was greater for sevoflurane and isoflurane, respectively, compared with halothane. Mean arterial pressure was similar for ail thre anesthetic agents. Respiratory rate for sevoflurane and isoflurane was less than that for halothane. This apparent respiratory depression correlated with greater increase in Pa-CO2 and decreased pH when sevoflurane and isoflurane were compared with halothane. Recovery from sevoflurane anesthesia was qualitatively similar and superior to recovery from isoflurane and halothane, respectively. Time to standing did not differ significantly between sevoflurane and isoflurane, but was shorter than halothane. Conclusions-Sevoflurane induced cardiorespiratory effects that were comparable to those of isoflurane and halothane. Cardiac output was greater and respiratory rate was less than that for halothane at 1.5 MAC. Sevoflurane anesthesia was characterized by good control of anesthesia depth during induction, maintenance, and recovery. Recovery time after sevoflurane anesthesia was comparable to that for isoflurane, and recovery was smooth and controlled in a manner consistent with recovery from halothane.