Entropy correlates with Richmond Agitation Sedation Scale in mechanically ventilated critically ill patients

Sedation is routinely used in intensive care units. However due to absence of objective scoring systems like Bispectral Index and entropy our ability to regulate the degree of sedation is limited. This deficiency is further highlighted by the fact that agitation scores used in intensive care units (ICU) have no role in paralyzed patients. The present study compares entropy as a sedation scoring modality with Richmond Agitation Sedation Scale (RASS) in mechanically ventilated, critically ill patients in an ICU. Twenty-seven, mechanically ventilated, critically ill patients of either sex, 16-65 years of age, were studied over a period of 24 h. They received a standard sedation regimen consisting of a bolus dose of propofol 0.5 mg/kg and fentanyl 1 μg/kg followed by infusions of propofol and fentanyl ranging from 1.5 to 5 mg/kg/h and 0.5 to 2.0 μg/kg/h, respectively. Clinically relevant values of RASS for optimal ICU sedation (between 0 and -3) in non-paralyzed patients were compared to corresponding entropy values, to find if any significant correlation exists between the two. These entropy measurements were obtained using the Datex-Ohmeda-M-Entropy™ module. This module is presently not approved by Food and Drug Administration (FDA) for monitoring sedation in ICU. A total of 527 readings were obtained. There was a statistically significant correlation between the state entropy (SE) and RASS [Spearman's rho/r_s = 0.334, p < 0.0001]; response entropy (RE) and RASS [Spearman's rho/r_s = 0.341, p < 0.0001]). For adequate sedation as judged by a RASS value of 0 to -3, the mean SE was 57.86 ± 16.50 and RE was 67.75 ± 15.65. The present study illustrates that entropy correlates with RASS (between scores 0 and -3) when assessing the level of sedation in mechanically ventilated critically ill patients.