Bispectral index (BIS) and suppression ratio (SR) as an early predictor of unfavourable neurological outcome after cardiac arrest

Abstract

Introduction: Predicting the neurological outcome after cardiopulmonary resuscitation (CPR) is extremely difficult. We tested the hypothesis whether monitoring of bispectral index (BIS) and suppression ratio (SR) could serve as an early prognostic indicator of neurological outcomes after CPR.

Methods: Cerebral monitoring (BIS, SR) was started as soon as possible after initiation of CPR and was continued for up to 72h. The functional neurological outcome was measured on day 3, day 7 and again one month after CPR via a clinical examination and assessment according to the cerebral performance category score (CPC).

Results: In total 79 patients were included. Of these, 26 patients (32.9%) survived the observation period of one month; 7 of them (8.9%) showed an unfavourable neurological outcome. These 7 patients had significantly lower median BIS values (25 [21;37] vs. 61 [51;70]) and higher SR (56 [44;64] vs. 7 [1;22]) during the first 4h after the initiation of CPR. Using BIS<40 as threshold criteria, unfavourable neurological outcome was predicted with a specificity of 89.5% and a sensitivity of 85.7%. The odds ratio for predicting an unfavourable neurological outcome was 0.921 (95% CI 0.853-0.985). The likelihood to remain in a poor neurological condition decreased by 7.9% for each additional point of BIS, on average.

Conclusion: Our results suggest that BIS and SR are helpful tools in the evaluation of the neurological outcomes of resuscitated patients. Nevertheless, therapeutic decisions have to be confirmed through further examinations due to the far-ranging consequences of false positive results.

Keywords: Bispectral index; Cardiac arrest; Cardiopulmonary resuscitation; Cerebral function; Neurological outcome.