Validating the Sedation-Agitation Scale with the Bispectral Index and Visual Analog Scale in adult ICU patients after cardiac surgery.

Abstract

To validate the Sedation-Agitation Scale (SAS) with the Visual Analog Scale (VAS) and Bispectral Index (BIS) in adult ICU patients after cardiac surgery. Prospective study comparing blinded evaluations of the SAS, VAS and BIS. Forty-two-bed multidisciplinary ICU. Convenience sample of 39 adults after cardiac surgery. Bispectral Index 3.2 was continuously recorded using the Aspect A-1000 and evaluators were blinded to this value. The bedside nurse and a trained researcher independently rated wakefulness using a 100 mm VAS upon patient arrival on the ICU, at first awakening, when ventilator weaning was started and after extubation; the researcher also evaluated patients using SAS. Upon arrival on the ICU, the median SAS score was 2 (interquartile range = 1-3), the mean VAS was 26+/-30 and the mean BIS was 70+/-16. Twenty-four patients underwent a trial of weaning from mechanical ventilation with a SAS of 4 (IQR = 4), VAS of 86+/-12 and BIS of 87+/-10. SAS correlated well with VAS performed by one researcher (r = 0.91, p < 0.001) or by 19 different bedside nurses (r = 0.43, p < 0.001) and with BIS 3.2 (r = 0.60, p < 0.001). The correlation between SAS and BIS was reduced in patients with above average electromyogram (EMG) power. As a measure of construct validity, significant differences were noted for the BIS, SAS, VAS and EMG between ICU arrival and extubation (all p < 0.001). Sedation-Agitation Scale and BIS are valid measures of wakefulness after cardiac surgery, but EMG interference may affect the accuracy of BIS for a small percentage of patients not receiving neuromuscular blockade.