During
propofol-
nitrous oxide (N2O)
anesthesia, volatile
anesthetics are frequently administered to treat signs of inadequate
anesthesia and to decrease the possibility of
intraoperative awareness. Because the clinical effects of this combination have not been examined rigorously, we used data from the 1989-90 Phase IV clinical trial with
propofol to evaluate recovery from propofol-N2O
anesthesia with and without supplementation with
isoflurane. In this study involving 15,806 patients at 1722 institutions,
propofol was administered for induction and maintenance of
anesthesia with N2O for procedures lasting less than 60 min. At the discretion of the anesthesiologist, volatile
anesthetics were administered as needed during maintenance of
anesthesia (the incidence of use of inhaled
anesthetics was 14.7% for
isoflurane, 2.2% for
enflurane, and 0.2% for
halothane). Other intraoperative medications included
opioid analgesics, muscle relaxants, and
anticholinergic drugs. The present study concerns the subset of 7796 patients given propofol-N2O maintenance
anesthesia (intermittent bolus or continuous infusion) with or without
isoflurane supplementation for procedures lasting less than 60 min.
Isoflurane was used more frequently for procedures lasting 30-60 min than for those less than 30 min. Nevertheless, the maintenance dose of
propofol was significantly (P < 0.05) less with
isoflurane (178 vs 235 mg). Adjunctive use of
isoflurane prolonged the time to awakening and to becoming oriented, but discharge times were similar for the two groups. The incidence of
postoperative nausea,
vomiting, recall, and excitement did not differ between the two groups. We conclude that the addition of
isoflurane to a propofol-N2O
anesthetic does not alter recovery from
anesthesia.