The comparability of bispectral index and state entropy index during maintenance of sufentanil-sevoflurane-nitrous oxide anesthesia.

BACKGROUND: Manufacturers recommend maintaining Bispectral (BIS) or Spectral Entropy (State Entropy, SE) indexes between 40 and 60 during the maintenance of anesthesia. We compared these indexes during this period. METHODS: Data were obtained from 58 patients receiving sufentanil-sevoflurane-nitrous oxide anesthesia. The anesthesiologist was blinded to BIS and SE. Artifact-free concurrent BIS and SE values (7792 pairs), automatically recorded at 1-min intervals, were compared using Bland-Altman analysis, Kappa coefficient for agreement and crude proportion of agreement. The occurrence of errors of judgment (Type 1 defined as one parameter <40 and the other >60, or Type 2 defined as BIS and SE values on different sides of a threshold [40 or 60]) was also counted. RESULTS: Bias was -2 with limits of agreement of -18 and 9. Kappa BIS/SE obtained from all patients was 0.537 +/- 0.147; crude agreement >0.80 was observed in 45% of patients. Type 1 number of errors of judgment corresponded to two instances. Median and interquartile values of Type 2 number of errors of judgment were 4.5 [3.0-6.0] when considering a difference between BIS and SE more than 5. CONCLUSION: Although limits of agreement between BIS and SE were large, Kappa value moderate, and crude agreement <0.80 in more than half of the patients, making completely contradictory decisions (e.g., deepening the anesthetic based on one parameter and lightening it based upon the other) would have been exceptional. More common would have been a risk of error between no change versus increasing or decreasing anesthetic depth.

Does monitoring bispectral index or spectral entropy reduce sevoflurane use?

A decrease in volatile anesthetic consumption has been demonstrated using bispectral index (BIS), whereas data concerning spectral entropy are lacking. One hundred and forty adult patients scheduled for surgical procedures lasting more than 1 h were prospectively randomized to receive an anesthetic controlled either by BIS or by spectral entropy or solely by clinical variables. Anesthesia was induced with propofol and sufentanil. Sufentanil was infused continuously thereafter. Sevoflurane was administered in 1 L/min O2/N2O. The sevoflurane concentration was adjusted according to conventional clinical variables in the standard practice group, whereas the 40-60 interval was applied for the BIS and spectral entropy-guided groups. The sevoflurane vaporizer was weighed before and after anesthesia, and consumption was calculated. Groups were comparable for demographic data except for weight (heavier in the spectral entropy-guided group, P < 0.05). Compared with standard practice, patients with BIS or spectral entropy monitoring required 29% less sevoflurane (normalized sevoflurane consumption to the weights of the patients and to the durations of anesthesia; both P < 0.03) and a similar sufentanil dose. An unintended improvement in the standard practice group (positive bias) was observed. In conclusion, BIS and spectral entropy monitoring have the same sparing effect of sevoflurane.