The association between intraoperative electroencephalogram-based measures and pain severity in the post-anaesthesia care unit.

This observational study aimed to identify simple electroencephalogram indices of inadequate intraoperative opioid-mediated nociceptive blockade and to compare these indices with routinely used clinical predictors of severe postoperative pain in adults. Intraoperative trend and waveform data (electrocardiogram, pulse oximetry and electroencephalogram) were collected, pain intensity in the post-anaesthesia care unit was quantified using an 11-point Verbal Rating Score, and opioid administration was recorded. Using the initial post-anaesthesia care unit Verbal Rating Score as the primary endpoint, the relationship between five possible explanatory variables--surgery type, depth of volatile anaesthesia (minimum alveolar concentration), electroencephalogram signs (state entropy, spindle-like activity and delta-band power) and estimated end-of-operation effect-site morphine concentrations--was examined. One hundred and thirteen patients were recruited, with 94 included in the final clinical and electroencephalogram data analysis. Fifty-two patients had moderate or severe pain (Verbal Rating Score > or = 5). State entropy was lower (46.5 +/- 2.9 vs 43.1 +/- 1.9, P = 0.04) and spindle-like activity higher (0.42 +/- 0.03 vs 0.50 +/- 0.02, P = 0.03) in the moderate/severe pain group. [corrected] These findings suggest that there is a modest association between electroencephalogram measures near the end of surgery and the severity of postoperative pain.

Rapid measurement of blood propofol levels: a proof of concept study.

OBJECTIVE: Despite many advantages over traditional volatile anaesthetic techniques, propofol total intravenous anaesthesia (TIVA) makes up a small percentage of general anaesthetics administered. One of the reasons for this is the absence of a clinically useful method for measuring blood propofol concentrations. We have designed and tested a prototype system for rapidly measuring blood plasma levels of propofol using solid phase extraction (SPE) methodology, coupled with colorimetric and spectrometric techniques. METHODS: Multiple venous blood samples were taken from 17 subjects during induction of anaesthesia with propofol. Samples were analysed in duplicate on both the prototype system and using High Performance Liquid Chromatography (HPLC). The prototype monitor response was calibrated against known methanol-based propofol standards and an estimate of the plasma concentration of propofol derived from regression analysis of the standard responses. RESULTS: Bland Altman analysis from a total of 87 samples gave 95% limits of agreement between the two methods of -0.34 to 0.42 microg mL(-1) (with no significant bias). The mean absolute prediction error was 8.9(7.5)%. The run time per sample on the prototype system was 4.5 min, including sample preparation. CONCLUSION: The results show that this methodology may be suitable for rapid and accurate clinical monitoring of propofol levels during general anaesthesia.

Cerebral cortical effects of desflurane in sheep: comparison with isoflurane, sevoflurane and enflurane.

BACKGROUND: Different volatile anesthetic agents have differing propensities for inducing seizures. A measure of the predilection to develop seizures is the presence of interictal spike discharges (spikes) on the electrocorticogram (ECoG). In this study, we investigated the propensity of desflurane to induce cortical spikes and made a direct objective comparison with enflurane, isoflurane, and sevoflurane. The ECoG effects of desflurane have not been previously reported. METHODS: After establishment of invasive monitoring and a parasagittal array of eight electrodes to record the ECoG; eight adult merino sheep were given a series of short inhalational anesthetics (using desflurane, enflurane, sevoflurane and isoflurane); each titrated to ECoG burst suppression. Anesthetic effect was estimated by the effects on the approximate entropy of the ECoG. The effect of anesthetic on the spike-rate in the ECoG was analyzed using a non-linear mixed-effect method with a sigmoid Emax model. RESULTS: A similar 'depth of anesthesia' was achieved for each agent, as estimated by the approximate entropy. The mean (SD) values of Emax for the spike-rate vs. approximate entropy relationship were desflurane 0.5 (0.9), enflurane 17.2 (4.0), isoflurane 0.7 (1.2), and sevoflurane 5.3 (1.2) spikes/min. The spike rate caused by desflurane was similar to isoflurane and significantly lower than that of enflurane (P < 0.001), and sevoflurane (P = 0.009). CONCLUSION: Desflurane induces minimal cerebral cortical spike activity when administered to burst suppression, consistent with its low propensity for inducing seizures in non-epileptic brains. The agents can be ranked by their relative ability to cause spike activity: enflurane >> sevoflurane > isoflurane = desflurane.