Controversias sobre el manejo de la fluidoterapia en cirugía abdominal / Controversies in fluid management during abdominal surgery

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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.

Correlation beween AAI-index and the BIS-index during propofol hypnosis: a clinical study.

OBJECTIVE: To determine the degree of linearity and correlation between the anaesthetic depth indices BIS and AAI over a wide range of hypnotic depth using propofol. METHODS: 20 ASA I patients were studied during propofol induction. Co-induction with 0.05 mg fentanyl and 30 mg propofol iv before initiation of the study. Thereafter repeated doses of propofol 0.5 mg/kg iv. every minute until BIS < 30. Loss of responsiveness to verbal command was determined by repeated loud commands to the patient. BIS (Aspect 2000 XP, BIS algorithm 4.0, system rev. 3.12, Aspect Medical Systems; Natick, MA, U.S.A.) and AAI-index (A-Line Auditory Evoked Potential Monitor, version 1.4, Danmeter A/S; Odense, Denmark) were determined simultaneously (n = 15). BIS alone without acoustical stimulation was studied in a control group (n = 5). MAIN RESULTS: Both indices decreased with increasing dose, and there was a high correlation between the two (r2 = 0.82). The indices showed however different values and while BIS were quite linear, the AAI-index had a more on-offb ehaviour. CONCLUSION: The AAI-index correlates with the BIS-index during propofol hypnosis in the absence of surgical stimulation. Neither the BIS-index, heart rate, nor systemic blood pressure were influenced by the acoustical stimulation from the A-line monitor. Both indices decreased in relation to increasing doses of propofol, but the AAI-index was lower both before becoming unconscious, during transition to unconsciousness, and during the deeper levels of sedation. The AAI-index lacks linearity at both very low and higher levels of propofol sedation with a nearly on-off behaviour for wakefulness vs hypnosis.

Biasing effect of the electromyogram on BIS: a controlled study during high-dose fentanyl induction.

OBJECTIVE: A biasing effect of the electromyogram (EMG) on the Bispectral Index (BIS) may explain discrepancies in previous studies assessing BIS in the presence of neuromuscular activity. Our aims were: to evaluate variations of BIS in the presence of high EMG activity associated with muscular rigidity after administration of high-dose fentanyl; to compare muscular rigidity, as measured by the EMG variable of the BIS monitor, in patients who were administered two different dosages of fentanyl at induction of cardiac anaesthesia. METHODS: 26 patients undergoing CABG surgery, after premedication with morphine 0.15 mg/kg, were randomized to receive either fentanyl 50 mcg/kg (group F) or fentanyl 10 mcg/kg plus etomidate 0.2 mg/kg (group EF). The induction dose was administered over 2 minutes. Patients were manually ventilated with O2 via face mask. Five minutes after induction was complete, patients were clinically assessed using the Responsiveness portion of the Observer's Assessment of Alertness/Sedation scale (OAAS). Haemodynamic data were recorded and arterial blood samples obtained at the time of OAAS observation. Patients were administered a neuromuscular blocking agent only after the OAAS assessment. BIS (3.4) was recorded from an A-2000 EEG monitor (Aspect Medical Systems) using disposable sensors (BIS Sensor, Aspect Medical Systems) applied per manufacturer's instructions. Data were recorded on a PC for off-line analysis. RESULTS: At the time of OAAS observation, mean (95% CI) BIS in group F was 85 (77-92) compared to 67 (56-79) in group EF (p = 0.01). Similarly, mean (95% CI) EMG was 50 dB (45-56) in F and 41 dB (35-47) in EF (p = 0.01). Correlation between BIS and EMG was very high (r2 = 0.88). OAAS scores were significantly higher in group F (p = 0.03). Non significant correlation was observed between BIS and OAAS scores (r2 = 0.32, p = 0.1). Backward stepwise multiple regression analysis including EMG, pH, CO2, O2 and OASS scores showed EMG as strong predictor of BIS (p < 0.0001, r2 = 0.7). Regression of EMG against BIS yielded the equation: BIS = 3.7 + (1.6 x EMG). CONCLUSION: During fentanyl-induced muscular rigidity BIS recordings reflect EMG variations. When assessing BIS in the absence of neuromuscular blockade, it is necessary to evaluate the effect of EMG on BIS before making conclusions about depth of sedation. Fentanyl-induced rigidity appears to be a dose-related phenomenon which the EMG variable of BIS 3.4 is able to quantify.