The effects of remifentanl on bispectral index (BIS) and sedation are controversial. The aim of this study was to evaluate the effects of continuous remifentanil infusion (0.03 µg/min/kg) on sedation by using BIS and the modified Observer's Assessment of the Alertness/Sedation Scale (OAA/S) during midazolam induced sedation after achieving pain free state by brachial plexus block.

In this study 40 ASA physical status 1 or 2 adult patients scheduled to undergo upper extremity surgery under brachial plexus anaesthesia were included. After obtaining adequate brachial plexus block, patients were randomly allocated to two groups. All patents received a single dose of midazolam 2 mg intravenously and continuous infusion (2 mg/h). At 15 minutes after midazolam injection, Group C received saline infusion and Group R received additional remifentanil (0.4 µg/kg bolus plus continuous infusion (0.03 µg/kg/min)). The mean arterial blood pressure (MAP), heart rate (HR), SpO₂, respiration rate (RR), and BIS were recorded every 5 min after injection of midazolam. The patient's level of sedation was assessed using the modified OAA/S and BIS immediately after MAP, HR, SpO₂, and RR measurements.

There are no significant differences in MAP, HR, BIS, and the modified OAA/S between two groups but RR was significant reduced in Group R compared with Group C after remifentanil infusion.

The remifentanil showed no effect on BIS and the modified OAA/S during midazolam induced sedation under pain free state.