SummaryWe have investigated the relationship between changes in the middle latency auditory evokedpotentials during alternating periods of consciousness and unconsciousness produced by propofol infusion combined with spinal anaesthesia for total knee replacement. Eleven patients completed the study, of whom two had recollection of events after the onset of the anaesthetic. There were no SigniJicant diyerences in heart rate or systolic arterial pressure between any conscious and unconscious period. With the first change from consciousness to unconsciousness, latencies of Na, Pa and Nb increased from mean (SD) starting values of 20.0 (1.4), 31.7 (1.0) and 42.8 (1.6) ms to 22.5 (2.0), 39.3 (2.1) and 57.8 (4.4)ms, respectively. During successive transitions from unconsciousness to consciousness, awake latencies were slightly higher than those of baseline awake, whereas anaesthetised latencies were similar to the ones obtained during the first period of unconsciousness. The consistent changes demonstrated, suggest that the auditory evoked potentials could represent a reliable indicator of potential awareness during anaesthesia. Key wordsMeasurement techniques; auditory evoked potentials. Anaesthetics, intravenous; propofol.The objective measurement of anaesthetic depth and its implications for the production of a reliable monitor of awareness, remains a desirable but elusive goal in anaesthesia [I]. Previous attempts to obtain an index of anaesthetic depth have included the use of the spontaneous electroencephalogram [2] and its processed derivatives, the cerebral function monitor [3], the cerebral function analysing monitor [4], fast Fourier transformation (FFT) and aperiodic waveform analysis [5]. More recently, the change in lower oesophageal contractility associated with anaesthesia has been investigated and shown to be related to the end-tidal concentration of volatile anaesthetics [6]. It was, however, insufficiently discriminating at the interface between consciousness and unconsciousness to be used as a monitor of awareness [7], and proved to be unrelated to blood concentration of intravenous anaesthetics [8].The most promising area of investigation has been the auditory evoked potential (AEP), which appears to show specific changes in its early cortical components related to depth of anaesthesia. These changes are independent of the anaesthetic agent used [8-131 and are partially reversed by surgical stimulation [ 141, properties thought to be necessary to qualify as an indicator of anaesthetic depth [IS]. In a recent study [16], the early cortical AEP was shown to be 'able to demonstrate potential awareness' under isoflurane anaesthesia. During some of those studies, a partial recovery of the AEP was observed after temporary discontinuation of the anaesthetic before the start of surgery [8-131. However, the patients were not allowed to recover completely and no quantitative data were published.Using a purpose-built, computer-based system, capable of processing the raw EEG and obtaining the AEP in real time,...

We have studied 20 infants, aged 2.5-8 weeks, undergoing general anaesthesia for pyloromyotomy with either desflurane or isoflurane. Patients were anaesthetized with equivalent 1 MAC values for age and agent. A blinded observer recorded times to breathing, swallowing, movement, extubation and side effects after discontinuation of the agent. Recovery times in the desflurane group were significantly shorter than in the isoflurane group. The times to swallowing, movement and extubation in the desflurane group were 3.89 (SD 2.4) min, 5.33 (4.95) min, 7.5 (4.53) min, respectively, and 8.82 (2.40) min, 10.73 (3.93) min, 13.45 (4.20) in the isoflurane group. In addition, postoperative apnoea was documented in the isoflurane group but not in those infants receiving desflurane. There was no laryngospasm after extubation in either group. We conclude that desflurane possesses useful characteristics for recovery conditions in the infant and may be particularly useful in the ex-premature infant prone to apnoea and ventilatory depression.

Introduction The management of vacuum neck drains in head and neck surgery is varied. We aimed to improve early drain removal and therefore patient discharge in a safe and effective manner. Methods The postoperative management of head and neck surgical patients with vacuum neck drains was reviewed retrospectively. A new policy was then implemented to measure drainage three times daily (midnight, 6am, midday). The decision for drain removal was based on the most recent drainage period (at <3ml per hour). A further patient cohort was subsequently assessed prospectively. The length of hospital stay was compared between the cohorts. Results The retrospective audit included 51 patients while the prospective audit included 47. The latter saw 16 patients (33%) discharged at least one day earlier than they would have been under the previous policy. No adverse effects were noted from earlier drain removal. Conclusions Measuring drainage volumes three times daily allows for more accurate assessment of wound drainage, and this can lead to earlier removal of neck drains and safe discharge.

A Psion microcomputer controlled infusion system for alfentanil was assessed for the provision of post-operative analgesia in 14 patients who had undergone aortic bifurcation graft surgery. The system employed a pharmacokinetic model working in real time to deliver any selected target plasma concentration of alfentanil. The alfentanil infusion system was used for a mean time of 39 hours and for 96% of this time, patients were scored as having no pain or only mild pain. Severe pain was recorded for only 0.05% of the study time. The use of a pharmacokinetic delivery system may offer a convenient and simple method of providing postoperative analgesia with alfentanil.

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