[The concentration effects of isoflurane-N2O anesthesia on cardiovascular responses to skin incision]

To investigate the concentration effects of isoflurane-nitrous oxide anesthesia on cardiovascular responses to skin incision, we studied 24 non-premedicated patients undergoing lower abdominal operation. Anesthesia was induced with inhalation of 70% nitrous oxide and isoflurane, and maintained with 70% nitrous oxide and three different concentrations of isoflurane (1.25, 1.6, 1.95 MAC). Blood pressure and heart rate were recorded continuously before and after skin incision. Because more than half the patients with 1.95 MAC became hypotensive with systolic blood pressure of less than 80 mmHg just before the skin incision, it was difficult to define the values of MAC BAR (blocking adrenergic responses) in the present study. Cardiovascular responses at skin incision were not completely suppressed at 1.6 MAC isoflurane-N2O anesthesia and no further blocking effects were obtained at 1.95 MAC isoflurane-N2O anesthesia. These results suggest that higher concentration of isoflurane does not guarantee stronger protective effects on stimulation like skin incision.