Effects Of Propofol On The Minimum Alveolar Concentration (MAC) Of Sevoflurane In Adults

BACKGROUND: Sevoflurane is a new inhalational anesthetic, which has been widespreadly used in general anesthesia due to its unique pharmacokinetic profile. Propofol is often combined with sevoflurane to improve cardiovascular stability and to decrease the incidence of postoperative nausea and vomiting during anesthesia in adult. It is important to know the interaction between Sevoflurane and propofol in adults . Therefore, the purpose of this study was to determine the effects of propofol on the minimum alveolar concentration (MAC) of sevoflurane with five different target-controlled concentrations in adults.METHODS: Eighty-nine ASA I-II patients (40 males, 49 females) aged 20-50 yr, scheduled to undergo elective abdominal surgery requiring a skin incision of more than 10-cm-long.Patients were randomly assigned into one of five groups. Each group received propofol at different target-controlled concentrations of 0, 1, 2, 3, and 4μg/ml, respectively. Anesthesia was induced with 8% sevoflurane and intravenous remifentanil (1μg/kg) and succinycholine (1mg/kg). After tracheal intubation the patients in each group were assigned to a predetermined steady concentration of propofol. Target end-tidal sevoflurane concentrations were determined using the "up-and-down" method until at least six independent crossover pairs were observed in each group. After at least 15-min of equilibration at the target end-tidal anesthetic concentration and the return of neuromuscular function (train-of-four), skin incisions were performed. The patients' somatic responses (any purposeful bodily movement) were observed for 60 second after the incision. MAC of sevoflurane was determined using a logistic regression model. The interaction between sevoflurane and propofol was analyzed using the linear regression and correlation analysis. Heart rate (HR) and mean arterial blood pressure (MAP) were recorded before induction of anesthesia, before and 5 min after surgical incision.RESULTS: MAC of sevoflurane when used alone was 2.19%. Propofol decreased MAC of sevoflurane by 14.2%at the target-controlled concentration of 1μg /ml.The MAC reduction of sevoflurane was 31.9%,at 2μg /ml, 36.2%, at 3μg /ml and 50.7%, at 4μg /ml. The linear regression equation of the interaction between sevoflurane and propofol in adults was Y = 2.19-0.285X, r =-0.988. However, HR and MAP was significantly higher than the preincision value during the first 5 min after incision in all groups, and the increase of HR and MAP was 23.28±2.76%and 29.24±2.07% respectively among the five groups. (P < 0.01)CONCLUSION: Propofol decrease MAC of sevoflurane in a dose-dependent manner in adults. Propofol and sevoflurane interact in a additive manner to produce immobility to skin incision. Propofol has a less suppressive effect of sympathetic responses to surgical incision and it is necessary to combine with other narcotic analgesics during sevoflurane anesthesia.