Midazolam and awareness with recall during total intravenous anaesthesia

A double-blind study was undertaken to evaluate the influence of graded doses of midazolam on propofol infusion requirements, recovery characteristics and the quality of recovery, associated with propofol/alfentanil/O2 total intravenous anaesthesia (TIVA).

Ninety ASA Class I and II subjects scheduled for arthroscopic knee surgery were randomly allocated to receive either placebo (Group PLAC), or midazolam doses of 15, 30 or 45 micrograms.kg-1 (Groups M-15, M-30 and M-45, respectively). Anaesthesia was induced and maintained with propofol (infused initially at 100 micrograms.kg-1.min-1, and adjusted there after according to anaesthetic depth) and alfentanil (loading dose of 20 micrograms.kg-1, followed by infusion at 0.5 microgram.kg-1. min-1). Postoperatively, times to awakening, recovery, and discharge were evaluated, in addition to psychometric evaluations using the Trieger Dot Test (TDT).

The study was discontinued prematurely, as six patients unexpectedly experienced intraoperative awareness with recall (4/21 = 19.1% of patients with PLAC vs 2/69 = 2.9% of patients in the midazolam groups, P < 0.04). Induction requirements of propofol were found to be lower in the M-30 and M-45 groups when compared with PLAC (P < 0.05), whereas propofol infusion requirements were similar among groups. Times to awakening and discharge from the Recovery Room and Day Care Unit, as well as TDT scores, were no greater in any midazolam group than in PLAC.

Midazolam 30-45 micrograms.kg-1 decreases the amount of propofol required for anaesthetic induction, without influencing recovery profiles or patient discharge times from the Day Care Unit. Despite careful modulation of the propofol infusion rate, six patients unexpectedly experienced intraoperative awareness with recall, with the lowest incidence occurring in those groups where patients had received midazolam.