[Intraoperative awareness in balanced anesthesia. A literature review based on a randomized double blind study using fentanyl, pentazocine and ketamine]

Abstract

Since the first case report by Winter-bottom [106], the problem of intraoperative awareness or recall has received increasing attention from patients, anaesthesiologists and, more recently, even law courts [4, 20, 21, 78]. Our own interest in awareness derives from a study with the opiate agonist tramadol as a supplement to balanced anaesthesia, which revealed an unexpectedly high incidence of about 65% of patients who could recall intraoperative music [55]. It was the aim of the present randomized double-blind study to evaluate, under identical experimental conditions, what the incidence would be with other analgesic supplements to balanced anaesthesia (fentanyl, pentazocine and ketamine). Because few reports on this subject are available in the German literature, it was felt that the result should be discussed within a comprehensive review. PATIENTS AND METHODS. A total of 60 patients (ASA I-II, age 27-66 years, weight 48-93 kg) undergoing elective gynaecological surgery of at least 90 min duration were each randomly assigned to one of three study groups (F, fentanyl; P, pentazocine; K, ketamine). Premedication was performed with diazepam 10 mg p.o. the evening before surgery and pethidine 1 mg/kg i.m.+promethazine 1.5 mg/kg i.m.+atropine 0.5 mg i.m. 60 min before anaesthesia. Induction was performed with alcuronium (2 + 8 mg), methohexital (1.5 mg/kg) and a bolus dose of the analgesic supplement (F, 5 micrograms/kg; P or K, 2 mg/kg), followed by continuous infusion (F, 2 micrograms kg-1 h-1, P or K 0.8 mg kg-1 h-1). Endotracheal intubation was performed with succinylcholine (1 mg/kg). Patients were ventilated to normocarbia using a Takaoka respirator (4 breaths/min, tidal volume 1600 ml, N2O/O2 75:25). If insufficient anaesthesia was suggested by increases in blood pressure or heart rate to more than 20% of preinduction values, excessive sweating or lacrimation, enflurane (0.5-2 vol.%) was added for short periods of time. At the end of surgery, patients were ventilated with 100% O2, and the neuromuscular block antagonized using atropine 0.5 mg and neostigmine 1 mg. Without prior announcement, tape-recorded music (Mantovani, 3 min followed by 3 min silence) was played to all patients via earphones throughout the time period between intubation and the end of nitrous oxide administration. Vegetative parameters, cumulative and relative enflurane application times and retrospective judgement of quality of anaesthesia by the anaesthesiologist were documented. Post-operative recovery and pain were monitored using verbal rating scales. Patients were interviewed immediately after extubation and on the day after surgery to determine the incidence of dreams and recollection of music. Patients were classified as amnestic if they could not recall the music, even with prompting, and partially amnestic if they remembered the music but were unable to define the time when they had heard it. No amnesia was assumed if patients recalled the intraoperative music spontaneously. Groups were statistically compared by means of analysis of variance, Mann-Wilcoxon rank sum test and chi-square test. RESULTS. Mean duration of anaesthesia was 129-134 min in the subgroups. The total analgesic supplement dose was F 614 +/- 129 micrograms, P 238 +/- 38 mg, and K 230 +/- 50 mg (mean +/- SD). Enflurane substitution was necessary in 45 patients, regardless of the type of analgesic supplement. Mean cumulative enflurane application time was 26-28% in the treatment groups, corresponding to about 20% of anaesthesia duration. The most important reasons for enflurane substitution were increases in blood pressure (mostly in groups F and P) or heart rate (K). Recovery was fastest with F, followed by P, and slowest with K. Retrospective judgement of the quality of anaesthesia by the anaesthesiologist did not differ significantly between the treatment groups. Most (93%) of the patients were satisfied with their anaesthesia; 2 patients each who received P and K were dis