Remifentanil Administration During Monitored Anesthesia Care

This randomized, double-blind study was designed to evaluate the analgesic effectiveness and respiratory stability of remifentanil when administered as intermittent bolus injections, a variable-rate infusion, or a combination of a constant basal infusion supplemented with intermittent boluses during monitored anesthesia care (MAC). Forty-five patients undergoing extracorporeal shock wave lithotripsy (ESWL) procedures were randomly assigned to one of the three modes of remifentanil administration. All patients received midazolam 2 mg i.v., followed by a propofol infusion at 50 microg x kg(-1) x min(-1). Two minutes before administering a series of test shock waves: Group I received a remifentanil infusion of 0.1 microg x kg(-1) x min(-1), and a saline bolus (5 mL); Group II received a saline infusion and a remifentanil bolus (25 microg in 5 mL); and Group III received a remifentanil infusion of 0.05 microg x kg(-1) x min(-1), and a remifentanil bolus (12.5 microg in 5 mL). The average pain intensity was scored on an 11-point scale, with 0 = no pain to 10 = severe pain. During the ESWL procedure, pain was treated by increasing the study drug infusion rate by 25%-50% and administering 5-mL bolus injections of the study medication in Groups I (saline) and II (remifentanil 25 microg). In Group III, intermittent 5-mL boluses (remifentanil 12.5 microg) were administered as needed. Patients in Groups II and III reported lower pain scores in response to the test shocks. Significantly more remifentanil was administered in Group I (379 +/- 207 microg) than in Group II (201 +/- 136 microg). However, more interventions were required for the treatment of intraoperative pain in the intermittent bolus group (Group II). When remifentanil is administered as the analgesic component of a MAC technique, these data support the use of intermittent bolus doses (12.5-25 microg) alone or in combination with a basal infusion (0.05 microg x kg(-1) x min(-1)) as alternatives to a variable-rate continuous infusion.