We studied 160 ASA I-II patients, anaesthetized with propofol by infusion, using either a manually controlled or target-controlled infusion system. Patients were anaesthetized by eight consultant anaesthetists who had little or no previous experience of the use of propofol by infusion. In addition to propofol, patients received temazepam premedication, a single dose of fentanyl and 67% nitrous oxide in oxygen. Each consultant anaesthetized 10 patients in sequential fashion with each system. Use of the target-controlled infusion resulted in more rapid induction of anaesthesia and allowed earlier insertion of a laryngeal mask airway. There was a tendency towards less movement in response to the initial surgical stimulus and significantly less movement during the remainder of surgery. Significantly more propofol was administered during both induction and maintenance of anaesthesia with the target-controlled system. This was associated with significantly increased end-tidal carbon dioxide measurements during the middle period of maintenance only, but recovery from anaesthesia was not significantly prolonged in the target-controlled group. With the exception of a clinically insignificant difference in heart rate, haemodynamic variables were similar in the two groups. Six of the eight anaesthetists found the target-controlled system easier to use, and seven would use the target-controlled system in preference to a manually controlled infusion. Anaesthetists without prior experience of propofol infusion anaesthesia quickly became familiar with both manual and target-controlled techniques, and expressed a clear preference for the target-controlled system.

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To establish anesthesia with minimal respiratory and cardiovascular depression using propofol, the effects of varying the rate of delivery on anesthetic induction dose requirements and hemodynamic changes were studied in four groups of 20 patients each undergoing body surface surgery. All patients were premedicated with temazepam and received 1.5 micrograms/kg fentanyl 5 min before induction. Propofol was delivered at 50, 100, or 200 mg/min by the Ohmeda 9000 infusion pump (groups 1, 2, and 3, respectively) or by bolus of 2 mg/kg (group 4) until loss of verbal contact. Anesthesia was maintained thereafter with propofol infused at 6 mg.kg-1.h-1. Using slower infusion rates, induction took significantly longer (124, 92, 62, and 32 s in groups 1, 2, 3, and 4, respectively) and was achieved with significantly smaller doses of propofol (1.40, 1.96, 2.61, and 2.15 mg/kg in groups 1, 2, 3, and 4, respectively). Slow infusion (groups 1 and 2) caused less depression of systolic and diastolic blood pressure than rapid infusion (groups 3 and 4), but the differences were not statistically significant. Patients in groups 3 and 4 had significantly greater decreases in pulse rate and a greater incidence of apnea than did patients in group 1. There was no correlation between the size of the induction dose and subsequent maintenance requirements of propofol. The finding that the sleep dose of propofol is reduced at slower infusion rates has important practical and theoretical implications when considering the relative potencies of intravenous anesthetics.

A comparison was made of arterial pressures measured invasively from a radial arterial cannula and non-invasively from the middle finger using the 2300 Finapres (Ohmeda) during induction and maintenance of anaesthesia. Digital outputs of both pressures were captured directly onto computer hard disk; data recorded during flushing of the arterial line were excluded from analysis. We studied 53 patients undergoing cardiac, major vascular and neurosurgical procedures; 17705 comparisons of systolic, diastolic and mean pressure were analysed. Overall correlations between Finapres and invasive pressures were poor (r = 0.82, 0.68 and 0.78 for systolic, diastolic and mean pressures, respectively). The Finapres exhibited a high level of accuracy and precision in some recordings. However, patient data sets showed marked variability in average pressure differences (invasive minus Finapres) when examined individually or grouped by operation type. Unexplained variations in pressure difference with time and absolute pressure were observed also. Whilst providing useful beat-to-beat information on arterial pressure trends, the Finapres cannot be recommended as a universal substitute for invasive arterial pressure monitoring.