Administration of fentanyl before remifentanil-based anaesthesia has no influence on post-operative pain or analgesic consumption.

BACKGROUND: Remifentanil's short-acting analgesic effect and the potential of producing hyperalgesia is a challenge to post-operative pain control. This study investigated whether pre-treating the patients with fentanyl before remifentanil-based anaesthesia could reduce post-operative pain or analgesic consumption. METHODS: One-hundred patients admitted for anterior cruciate ligament repair were included in a double-blind study. Propofol and remifentanil were used for general anaesthesia. Group Pre received fentanyl 1.5 microg/kg intravenously (IV) and Group Post placebo before the remifentanil infusion. At the end of surgery, Group Pre received 1.5 microg/kg and Group Post received 3.0 microg/kg. Patient-controlled analgesia with fentanyl was used as analgesic rescue medication during the first 4 h post-operatively. Oxycodone 5 mg orally was taken as needed during the subsequent 4-24-h period. RESULTS: A mean dose of remifentanil 0.43 microg/kg/min was used for 90 min during surgery in both groups. There were no differences in the verbal rate scale (VRS) score or need of rescue analgesic medication between the groups during the first 4 h. Group Post had significantly less pain in the 4-24-h period after surgery, with a median VRS score of 'slight pain' vs. 'moderate pain' in Group Pre (P<0.05). The oxycodone consumption was similar in both groups. CONCLUSION: Pre-treatment with fentanyl 1.5 microg/kg IV yielded no reduction in post-operative pain or analgesic consumption after 90 min of remifentanil-based anaesthesia with 0.43 microg/kg/min of remifentanil.

Can the cerebral state monitor replace the bispectral index in monitoring hypnotic effect during propofol/remifentanil anaesthesia?

BACKGROUND: In 2004, the cerebral state monitor, CSM, was launched as a low-cost alternative to the bispectral index, BIS, for monitoring depth of sleep during anaesthesia. We tested whether the two monitors would reflect hypnosis equally during propofol/remifentanil anaesthesia. METHODS: During laparoscopy or breast/surface surgery, 55 non-paralyzed patients were monitored simultaneously with the BIS and the CSM. Trend curves for the indexes [BIS and cerebral state index (CSI)] were compared for congruence. The difference between the two indexes for the entire course was quantified, and the ability of the two monitors to separate awake from asleep during induction was described. RESULTS: In the majority of the patients, 87%, there was a good fit between the indexes. There were major deviations in seven patients, in whom CSI indicated that the patients were awake during parts of the course despite clinical sleep, correctly identified with the BIS. Both indexes separated awake from asleep during induction in the individual patient, but the overlap in values between patients was more pronounced for CSI. CONCLUSION: CSM and BIS show some important differences in measuring hypnotic state during clinical propofol/remifentanil anaesthesia.

Why do women wake up faster than men from propofol anaesthesia?

BACKGROUND: It has repeatedly been shown that female patients wake up faster from propofol anaesthesia than male patients. The reason for this is not clear. It is possible that female patients have a more rapid decline in plasma propofol concentration after termination of an infusion, or there could be gender differences in the sensitivity to propofol, making women wake up at higher concentrations. We tested the hypothesis that women wake up faster because of a more rapid decline in plasma propofol. METHODS: Sixty adult patients (30 female and 30 male; ASA I or II) undergoing lower limb surgery under regional anaesthesia, were enrolled in an open study. Propofol was given as the only hypnotic drug, administered by the plasma target control system (TCI) Diprifusor, titrated to bispectral index (BIS) values of 40-60. Blood samples for propofol measurements were taken just before the propofol infusion was stopped and when the patients woke up. RESULTS: The female patients woke up faster than the male patients (5.6 vs 8.2 min, P=0.003). The plasma propofol concentration declined more rapidly in the women (P=0.02). An additional significant finding was that the TCI algorithm had a better fit for the women than for the men, with a median prediction error (MDPE) of 2% in the female patients compared with 40% in the male patients (P<0.001). At emergence the men had a significantly higher measured propofol concentration than the women (P=0.05). CONCLUSION: The female patients had a more rapid decline in plasma propofol at the end of infusion. Gender differences in pharmacokinetics could explain the faster emergence for female patients after propofol anaesthesia, and gender differences in propofol sensitivity may also be present.

Bispectral index, serum drug concentrations and emergence associated with individually adjusted target-controlled infusions of remifentanil and propofol for laparoscopic surgery.

BACKGROUND: Target-controlled infusions (TCI) are used to simplify administration and increase precision of i.v. drugs during general anaesthesia. However, there is a limited relationship between preset targets and measured concentrations of drugs and between measured concentrations and measures of brain function, such as the bispectral index (BIS). METHODS: We set out to evaluate the performance of TCI devices for propofol (Diprifusor) and remifentanil (Remifusor, prototype), during laparoscopic cholecystectomy in 21 patients. We also checked if there was any correlation between serum concentrations of propofol and BIS during individually adjusted anaesthesia. RESULTS: The Diprifusor and Remifusor had a median absolute performance error of 60% and 25% respectively. Propofol concentrations were underpredicted by a median of 60%, and remifentanil concentrations were slightly overpredicted by a median of 7%. When anaesthesia was adjusted to keep BIS values between 45 and 60, no correlation existed between measured concentrations of propofol and the corresponding BIS values, although both BIS and serum propofol concentration discriminated well between the awake and asleep states. Emergence was rapid and uneventful in all patients. Female patients had a more rapid emergence than male patients (6.6 and 11.6 min respectively). CONCLUSIONS: TCI devices for remifentanil and propofol result in large variation in measured serum concentrations. The lack of correlation between BIS and serum concentrations of propofol adds to the debate about whether BIS measures hypnosis as a graded state during surgery. This study confirms that women wake up faster than men, but provides no explanation for this repeatedly shown difference.

Bispectral index, predicted and measured drug levels of target-controlled infusions of remifentanil and propofol during laparoscopic cholecystectomy and emergence.

BACKGROUND: Target-controlled infusions (TCI) have been launched as simple, accurate and reliable delivery systems of intravenous drugs. Bispectral index of EEG (BIS) seems promising in measuring hypnotic effect of anaesthetic drugs. The aims of this study were to evaluate the accuracy of TCI systems in patients undergoing laparoscopic cholecystectomy and to correlate measured drug levels to BIS values. Data were analysed for possible gender differences during emergence. METHODS: After written informed consent, 20 patients were enrolled in an open study. Remifentanil was set at 7.5 ng/ml as target throughout the whole procedure, and propofol at 5 microg/ ml at induction and 3 microg/ml after intubation. Values in blood samples of remifentanil and propofol were correlated to the estimated values and to systolic blood pressure and BIS. BIS values and measured drug levels during emergence and emergence time were compared for the two sexes. RESULTS: Measured drug values varied considerably from the set target with a prediction error of -22% for remifentanil and 49% for propofol. The anaesthesia level was regarded as quite deep with a mean BIS during stable surgery of 42 +/- 7, and at this level we found no correlation between measured values of either of the two drugs and BIS. The emergence time was significantly shorter for women (12.6 +/- 2.5 min) than for men (19.0 +/- 4.2 min) (P=0.001), with no significant differences in measured levels of propofol or remifentanil or BIS during the emergence period. CONCLUSION: Present systems for TCI of remifentanil and propofol result in large intra- and interindividual variations in measured drug levels, and measured levels differ from target. There may be possible interaction between the two anaesthetics at a pharmacokinetic level. Within the level of anaesthesia studied here, BIS was not an indicator of the actual drug levels. Women woke up significantly faster than men.