Anaesthesia
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A technique of balanced anaesthesia involving propofol infusions and a rapidly metabolised opioid offers advantages over traditional anaesthetic techniques for eye surgery. The most appropriate mode of delivery of propofol is by a 'Diprifusor' target controlled infusion system. This paper discusses the use of a 'Diprifusor' target controlled infusion system for eye surgery. Published data are reviewed and the results of a retrospective analysis of 138 successive eye surgery patients are presented.
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The development of new short-acting anaesthetic drugs, improved drug assay techniques and the availability of reliable infusion systems opened the field of clinical pharmacokinetics and pharmacodynamics. The tri-exponential drug concentration decay complicates the definition of therapeutic dosage regiments and prevents straightforward prediction of recovery from drug effects. The context-sensitive half-time, the time required for drug blood concentration to decrease to half its value, provides a useful comparative predictor of drug concentration decline after infusion. ⋯ The rationale for drug infusion is reduction of fluctuating drug concentrations and drug effects. A variability similar to that observed with the use of inhalation agents, must be achieved by the choice of an appropriate pharmacokinetic model. The use of a target controlled infusion device, delivering proportional changes based on pharmacokinetic principles, allows titration of the concentration against clinical effect in individual patients.
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The pharmacokinetic profile of propofol is an advantage in neurosurgery, where the rapid return of cognitive function is essential for an early postoperative assessment of neurological status. Administration of propofol by 'Diprifusor' target controlled infusion allows induction of anaesthesia in neurosurgical patients without significant reduction of mean arterial pressure or occurrence of apnoeic episodes. This short paper describes our experience of 'Diprifusor' target controlled infusion for neuroanaesthesia in a series of 20 patients undergoing craniotomy for excision of epileptic foci. The results have been compared with ten similar operations where propofol infusion was controlled manually.
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Randomized Controlled Trial Clinical Trial
Power spectral analysis of the electroencephalogram during increasing end-expiratory concentrations of isoflurane, desflurane and sevoflurane.
We studied the effects of increasing end-expiratory concentrations of isoflurane (0.3, 0.6, 0.9, 1.2 vol.%) (n = 12 patients), desflurane (1.5, 3.0, 4.5, 6.0 vol.%) (n = 12 patients) and sevoflurane (0.5, 1.0, 1.5, 2.0 vol.%) (n = 12 patients) on power spectral analysis of the electroencephalogram (EEG). Spectral edge frequency (SEF), total power (TP) and relative power in the delta, theta, alpha and beta band were calculated. ⋯ SEF decreased, TP and relative power in the delta and theta band increased, power in the beta band decreased in a dose-dependent fashion with comparable regression lines. This indicates that MAC equivalent administration of isoflurane, desflurane and sevoflurane in clinically applied dose ranges is associated with equipotent EEG suppression.
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Randomized Controlled Trial Multicenter Study Comparative Study Clinical Trial
TCI compared with manually controlled infusion of propofol: a multicentre study.
This prospective, randomised multicentre study was designed to determine the clinical profile of 'Diprifusor' target controlled infusion compared with manually controlled infusion of propofol in 562 patients, aged 18-85 years, in a range of surgical procedures in 29 centres. The dose of propofol required for loss of consciousness was statistically significantly lower in the target controlled infusion group [1.69 (0.50) vs. 2.31 (0.75) mg.kg-1, p < 0.001] but the overall rate of propofol administration was slightly, but significantly, higher [12.1 (5.1) vs. 11.0 (6.0) mg.kg-1.h-1, p < 0.05]. The target concentration (CT) required for induction decreased with increasing age and ASA class, with premedication and with the administration of an opioid before induction. ⋯ Despite the lack of experience of most investigators in using target controlled infusion, the clinical profiles of both propofol administrations were similar. Data suggest that the clinical profile of target controlled infusion may be improved with experience, for example by more active titration of CT to effect. Target controlled infusion may well become the preferred choice for anaesthetists.