THE MINIMUM ALVEOLAR CONCENTRATION (MAC) AND HEMODYNAMIC-EFFECTS OF HALOTHANE, ISOFLURANE, AND SEVOFLURANE IN NEWBORN SWINE

To determine the minimum alveolar concentration (MAC) and hemodynamic responses to halothane, isoflurane, and sevoflurane in newborn swine, 36 fasting swine 4-10 days of age were anesthetized with one of the three volatile anesthetics in 100% oxygen. MAC was determined for each swine. Carotid artery and internal jugular catheters were inserted and each swine was allowed to recover for 48 h. After recovery, heart rate (HR), systemic systolic arterial pressure (SAP), and cardiac index (CI) were measured awake and then at 0.5, 1.0, and 1.5 MAC of the designated anesthetic in random sequence. The (mean ± SD) MAC for halothane was 0.90 ± 0.12%; the MAC for isoflurane was 1.48 ± 0.21%; and the MAC for sevoflurane was 2.12 ± 0.39%. Awake (mean ± SD) measurements of HR, SAP, and CI did not differ significantly among the three groups. Compared to the awake HR, the mean HR decreased 35% at 1.5 MAC halothane (P < 0.001), 19% at 1.5 MAC isoflurane (P < 0.005), and 31% at 1.5 MAC sevoflurane (P < 0.005). Compared to awake SAP, mean SAP measurements decreased 46% at 1.5 MAC halothane (P < 0.001), 43% at 1.5 MAC isoflurane (P < 0.001), and 36% at 1.5 MAC sevoflurane (P < 0.005). Mean SAP at 1.0 and 1.5 MAC halothane and isoflurane were significantly less than those measured at equipotent concentrations of sevoflurane (P < 0.005). Compared to awake CI, mean CI measurements decreased 53% at 1.5 MAC halothane (P < 0.001) and 43% at 1.5 MAC isoflurane (P < 0.005). Mean CI did not change significantly between the awake measurement and 1.5 MAC sevoflurane. Mean CI at both 1.0 and 1.5 MAC halothane and isoflurane were significantly less than those measured at equipotent concentrations of sevoflurane (P < 0.01). We conclude that both halothane and isoflurane depress the hemodynamics in newborn swine to a significantly greater extent than does sevoflurane at equipotent concentrations.