Effects of heart rate, blood pressure and bronchomotor tone of halothane, enflurane and isoflurane in young fit patients.

A prospective study was undertaken on 169 healthy young patients undergoing elective ear, nose and throat surgery to assess the intraoperative effects on heart rate, blood pressure and bronchomotor tone of MAC in nitrous oxide concentrations of halothane (0.4 to 0.6%), isoflurane (0.6 to 0.8%) and enflurane (0.8 to 1%). All the agents produced a progressive slowing of the heart rate during anesthesia. Halothane did so most profoundly, resulting in a maximum slowing of 40 beats-1 compared with a maximum slowing of about 20 beats min-1 with both isoflurane and enflurane. The three volatile agents also produced progressively similar degrees of hypotension during anesthesia. The hypotension produced by enflurane occurred earliest and was most profound; that produced by isoflurane occurred less early and was less severe, but occurred earlier and was more severe than that produced by halothane. Neither halothane, isoflurane nor enflurane appeared to have any effect on bronchomotor tone.