[Incidence and quality of dreaming during anesthesia with propofol in comparison with enflurane]

Since the introduction of propofol into clinical practice, dreaming during general anaesthesia has been frequently reported with this drug. We investigated the incidence and character of these dreams with regard to distinction from intraoperative awareness and in comparison with habitual dreams or dreams during general anaesthesia with enflurane.

A total of 230 patients (ASA I-II) undergoing minor elective surgery were randomly assigned to one of two groups. Both groups received the same premedication (1 mg flunitrazepam) the previous evening. After induction using etomidate 2 mg/kg, anaesthesia in group I was maintained using 0.8%-1.5% enflurane supplemented in the sense of "balanced anaesthesia" with fentanyl, vecuronium, and nitrous oxide. Anaesthesia in group II was induced with propofol 2 mg/kg. After a saturation phase of approximately 10 mg/kg.h, 5-6 mg/kg.h was administered for maintenance supplemented by fentanyl, Vecuronium, and N2O as in group I. Interviews were conducted preoperatively, just after recovery from anaesthesia, and 24 h later. We inquired about preoperative fears or concerns, sensory perceptions, and the incidence and character (pleasant, unpleasant, indifferent) of habitual dreams. After recovery the patients were asked if they had had any conscious perceptions, whether they believe them to be dreams or reality, and repeated the preoperative questions as to common feelings and the character of sensory perceptions.

The two groups were not entirely comparable due to the distribution of sex and age, but we did not find any differences in preoperative grades of fear and incidence of dreams. Of the propofol patients, 60% dreamed intraoperatively versus 11% in the enflurane group. No evidence of any intraoperative awareness was found. Because of the low incidence of dreams in the enflurane group, a comparison of detailed information between the groups could not be provided. Except for 1, all patients in the propofol group had very pleasant dreams compared to their habitual dreams (4.5% in the enflurane group). One day after surgery 37% of all patients in the propofol group remembered having dreamed intraoperatively. We did not found any correlation to the incidence of habitual dreaming, preoperative fear, age, sex, duration of anaesthesia, or total dose of propofol. Furthermore, intraoperative dreams differed from habitual dreams in character and content.

We conclude that sensory experiences during propofol anaesthesia are not stimulus-related perceptions or awareness, but dreams similar to normal ones. In view of the absence of clear signs of stimulus-related response, we presume that dreaming is a specific side effect of propofol. Because of the absence of difficulties, dreaming during propofol anaesthesia appears not to be a disadvantage with regard to the quality of anaesthesia.