Continuous infusion of midazolam during anaesthesia and postoperative sedation after maxillofacial surgery

The clinical effects and pharmacokinetics of 24 h infusion of midazolam (MDZ) during major maxillofacial surgery and postoperative observation in an Intensive Care Unit (ICU) were studied in 20 patients. During anaesthesia, infusion of MDZ at 5 mg/h combined with 67% nitrous oxide, 1.8 (s.d. = 0.8) mg of fentanyl, and 26.5 (s.d. = 11.4) mg of vecuronium, adequately suppressed clinical responses to surgical nociceptive stimuli. Postoperatively, infusion of MDZ was continued in the ICU at 5 mg/h until 9 a.m. of the first postoperative day for sedation of the intubated but spontaneously breathing patients. The depth of sedation in the ICU was scored from 1-5 (1 = "awake and tense", 5 = "unable to communicate"). During infusion the sedation score decreased from 3.8 after ICU arrival to 2.2 at 8 a.m. of the first postoperative day. Neither ventilatory nor circulatory depression were observed. After cessation of MDZ, recovery from sedation was fast. The degree of amnesia was low. During constant rate infusion no increase in plasma concentration of either MDZ or metabolites occurred. T1/2 beta of MDZ after cessation was 125 min (range 90-320) and its total body clearance was 10.5 ml/kg/min (s.d. = 3.1). The volume of distribution, clearance and T1/2 beta were significantly longer in women than in men. It was concluded that 24 h of MDZ infusion at 5 mg/h caused satisfactory ICU sedation with fast recovery, but that individual tailoring of the infusion rate may still improve the quality of sedation.