RAPID 1-PERCENT INCREASES OF END-TIDAL DESFLURANE CONCENTRATION TO GREATER-THAN 5-PERCENT TRANSIENTLY INCREASE HEART-RATE AND BLOOD-PRESSURE IN HUMANS

Background: Large (0.5-1.0 MAC), rapid increases of desflurane to concentrations greater than 5% can transiently increase heart rate, mean arterial blood pressure (MAP), sympathetic nerve activity, and plasma epinephrine concentration. We tested the hypothesis that small (1% = 0.14 MAC), rapid increases of desflurane concentration to greater than 5% do not increase heart rate, blood pressure, and plasma catecholamine concentrations. Methods: Anesthesia was induced with intravenous propofol, 2 mg/kg, in 13 healthy male volunteers, 19-33 yr of age, and ventilation was controlled to maintain normocapnia. We gave 4% end-tidal desflurane in oxygen for 32 min and then imposed successive 1% increases in end-tidal desflurane concentration, each new concentration maintained for 4 min, to a final concentration of 12%. We measured heart rate, MAP and plasma catecholamine concentrations in the awake state, after 4 min at each 1% step, and at times of peak increase of MAP (greater than or equal to 10% change). Results: Increases in heart rate and blood pressure of more than 10% occurred with 1% step-increases in only 1 volunteer at 5% desflurane but in 7-10 (MAP) and 8-12 (heart rate) of the 13 volunteers at higher desflurane concentrations. The 1% increases in desflurane concentration to greater than 5% also transiently increased plasma epinephrine concentrations but not vasopressin concentration or plasma renin activity in those volunteers in whom MAP increased. Conclusions: Small (1%) increases in desflurane concentration to and greater than 6% can transiently increase heart rate, mean arterial pressure, and plasma epinephrine concentration. These data and those from a previous study indicate that these increases occur with a lesser frequency and magnitude than those associated with a single, rapid step from 4% to 12% end-tidal desflurane.