The safety and effectiveness of remifentanil as an adjunct sedative for regional anesthesia

We assessed the sedative potential of continuous infusions of remifentanil with a validated composite alertness scale in 160 patients (ASA physical st atus I or Il) undergoing hip replacement surgery with spinal block (n = 61) or hand surgery using brachial plexus block (n = 93). They were randomized to receive one of the following initial dose regimens in double-blinded fa shion: placebo or 0.04, 0.07, or 0.1 mu g.kg(-1).min(-1) remifentanil subse quently titrated to effect. Additional midazolam IV was allowed for adequat e sedation as required. The combined analysis of both surgery groups reveal ed a dose-related increase in achievement of sedation level greater than or equal to 2 within 15 min of the start of the study drug infusion; all remi fentanil dose comparisons with placebo reached significance (P < 0.001). Th e remifentanil 50% effective dose for a composite sedation level greater th an or equal to 2 within 15 min of the start of drug infusion was estimated as 0.043 mu g.kg(-1).min(-1) (95% confidence interval 0.01, 0.059). The req uirement for midazolam decreased with increasing remifentanil dose compared with placebo (P < 0.001). The median time to return to alertness after the end of infusion was 10-12 min in the remifentanil groups and 5 min in the placebo group. Significant incidences of nausea, pruritus, sweating, and re spiratory depression were reported during remifentanil infusions compared w ith placebo. The data suggest that remifentanil may be useful for supplemen tation of regional anesthesia, provided that ventilation is carefully monit ored. Implications: In this dose-finding, placebo-controlled study, remifen tanil infusions were used to provide sedation during spinal and brachial pl exus regional anesthesia. The 50% effective dose for achievement of sedatio n was 0.043 mu g.kg(-1).min(-1). Return to alertness occurred after 10-12 m in (median time). Remifentanil infusions can be used to supplement regional anesthesia, but this requires careful monitoring of ventilation.