Objective: To assess the effect of monitoring the encephalogram bispectral index (BIS) during outpatient surgery. Outcome measures were amount of propofol administered, awakening and discharge.
Material and methods: Forty consecutive outpatient surgery patients were studied. The patients gave informed consent and received general intravenous anesthesia with propofol administered through a laryngeal mask using a computerized system (Diprifusor(R)). Two groups were formed: in group A, BIS was monitored, although the information was hidden from the anesthesiologists, who used the usual signs (loss of blinking reflex, pupil size and hemodynamic response) to guide anesthesia; in group B the anesthesiologists used BIS monitoring to guide propofol administration. Measurements were blood pressure, heart rate and BIS at six times during the procedure (T1-T6). Other data recorded were age, weight, height, propofol consumption in relation to weight and duration of procedure, consumption of rocuronium and alfentanil, duration of propofol infusion, time from withdrawal of propofol until eye opening, duration of stay in the post-anesthesia intensive care unit and time until total recovery. A questionnaire assessed the presence of intraoperative awareness and degree of satisfaction. The data were analyzed by Student's t and a chi square tests, with statistical significance at p < 0.05.
Results: Demographic variables (age, weight and height) were similar, as were duration of propofol infusion, total dose of alfentanil and rocuronium, evolution of blood pressure and heart rate. Statistically significant differences in BIS were observed at two times, T4 and T5; total propofol administered was 32.6% lower in group B; and time until eye opening was significantly shorter in group B. No significant differences were observed for time until full recovery. No instances of intraoperative awareness were reported and satisfaction was high in both groups.
Conclusion: BIS monitoring allows for propofol titration that leads to a mean reduction of 32.6% in consumption, shortening the time until eye opening without causing intraoperative awareness or reducing patient satisfaction.