Anaesthesia
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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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Review Case Reports
Recurrent respiratory depression after total intravenous anaesthesia with propofol and alfentanil.
Since first commented upon by Lamarche in 1984, several cases of recurrent respiratory arrest after alfentanil infusions have been reported. In all these cases the alfentanil infusions have been used to supplement conventional anaesthetic techniques with nitrous oxide and/or inhalational agents and in most cases rather high total alfentanil doses have been administered. We have seen two cases of severe recurrent respiratory depression in healthy patients after relatively minor procedures performed under total intravenous anaesthesia with propofol-alfentanil infusions, air-oxygen ventilation and muscle relaxation, where the alfentanil doses administered were quite small. These cases are presented in detail and compared within a tabulated presentation with the earlier published cases of alfentanil-related recurrent respiratory depression.
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Randomized Controlled Trial Clinical Trial
Clinical utility of EEG parameters to predict loss of consciousness and response to skin incision during total intravenous anaesthesia.
We studied 30 female patients undergoing elective surgery, to assess the reliability of electroencephalogram spectral edge frequency and median frequency to predict loss of consciousness and movement in response to skin incision during total intravenous anaesthesia. Each patient received a different combination of propofol (1, 2, 3, 4, 5 or 6 micrograms.ml-1) and sufentanil (0.1, 0.2, 0.3, 0.5 or 1.0 ng.ml-1) target concentrations for induction of anaesthesia using target controlled infusions, assigned randomly. ⋯ The probabilities of 50% and 95% no response for spectral edge frequency were 13.4 Hz and 6.8 Hz, respectively. The variability of the data limited the predictive value, so that spectral edge frequency was a poor predictor and median frequency was no predictor of response in the individual patient during total intravenous propofol/sufentanil anaesthesia.