Effect of midazolam pretreatment on propofol sedation by closed-loop TCI during epidural anesthesia

Objective To compare the effect of midazolam pretreatment on propofol sedation using closed-loop target-controlled infusion (TCI) between two age groups - the adult and the aged. Methods Forty-eight ASA Ⅰ-Ⅱ patients of both sexes weighing 45-81 kg undergoing elective lower abdominal or lower extremity operation under epidural anesthesia were divided into two age groups : (A) the adult group (18-39 yrs) and (B) the aged group (66-79 yrs). The two groups were further divided randomly into 2 subgroups : midazolam subgroup ( n=12) received midazolam 0.04 mg·kg-1 10 min before propofol TCI and placebo subgroup ( n = 12) received normal saline instead of midazolam 10 min before propofol TCI. The patients were unpremedicated. An intravenous line was established before operation, which was connected to a TCI system comprising a Graseby 3500 infusion pump and a closed-loop TCI automatic control system. BP, HR, SpO2 and BIS were continuously monitored during operation. During epidural anesthesia the patients were sedated with propofol administered by TCI. The initial target blood concentration of propofol was set at 1.5μg·ml-1 . The level of sedation was assessed by OAA/S scale (5 = alert,0 = no response to prodding). The target blood propofol concentration was then increased or decreased in 0.5μg·ml-1 increment to maintain OAA/S score at 3. The BIS value at this level of sedation (OAA/S=3) was used as feedback in controlling TCI of propofol. The induction dose and the total dose of propofol, induction time and emergence time (OAA/S=5) were recorded. Results Midazolam premeditation significantly reduced the induction dose and total dose of propofol, shorten the induction time and prolonged the emergence time compared with placebo in both groups, especially in the aged group (P0.05) . The incidence of hypotension and respiratory depression were significantly higher in the aged group than those in the adult group ( P 0.05). Conclusion Midazolam premedication significantly reduces the dose of propofol needed to induce and maintain sedation during epidural anesthesia especially in the aged. Midazolam premedication significantly increases the incidence of hypotension and respiratory depression induced by propofol sedation in the aged.