Comparing Entropy and the Bispectral index with the Ramsay score in sedated ICU patients

Abstract

Objective: ENTROPY is a new anesthetic depth monitor based on the analysis of the EEG signal. Our aim has been to evaluate sedation of intubated surgical critically ill patients by means of the Ramsay sedation score, the Bispectral index and ENTROPY, and to analyse the correlation between these variables.

Methods: Sedation was evaluated every 15 min for a 1 h period in 50 non-paralysed postoperative critically ill, intubated patients, enrolled over a 6 month period. A 5 min steady-state period was allowed before each assessment. Both the Bispectral index and the Entropy parameters Response Entropy (RE) and State Entropy (SE), were collected before assessing the Ramsay scale.

Results: Mean values for SE, RE and BIS were 53 +/- 27, 60 +/- 30, and 62 +/- 24 respectively. The median value for the Ramsay was 6 (range 1-6). Significant correlation was found between the four variables (SE-BIS: r = 0.79, p < 0.001; RE-BIS: r = 0.80, p < 0.001; SE-Ramsay: rho = -0.71, p < 0.001, RE-Ramsay: rho = -0.72, p < 0.001; BIS-Ramsay: rho = -0.78, p < 0.001; RE-SE: r = 0.98, p < 0.001). An overlap of BIS and Entropy values for every Ramsay score value between 4-6 was found.

Conclusions: ENTROPY, BIS and Ramsay score values correlate significantly in sedated postoperative ICU patients. ENTROPY does not appear superior to BIS for the assessment of sedation in this context.