Initial bispectral index may identify patients who will awaken during therapeutic hypothermia after cardiac arrest: A retrospective pilot study

AimPatients sustain a range of neurologic injuries after cardiac arrest, and determining which patients should be treated with therapeutic hypothermia (TH) is complex, often confounded by sedation and neuromuscular blockade (NMB). We evaluated bispectral index (BIS) monitoring as a tool to identify adult patients that awakened during therapeutic hypothermia.MethodsReview of prospectively collected registry data, with retrospective chart review of patient descriptions during hypothermia. Data are presented as median (interquartile range).Results7 of 309 patients (2.2%) treated with TH over 6 years awoke (followed commands) prior to completing hypothermia. Median age was 58 (54–66) years; 71% were male, cardiac arrest was witnessed in 6 (86%) and out-of-hospital in 6 (86%), and 4 patients (57%) were transferred from another hospital. 5 patients (71%) had an initial rhythm of ventricular tachycardia or fibrillation, time to return of spontaneous circulation was 17 (12–23) min. The BIS value after first NMB dose during TH was 63, 45, 43, 52, 62, 54, and 42 (median 52, IQR 44–58, 95% confidence interval 46–58). The median BIS value in the remaining data set (n = 302) was 18 (6–36), p < 0.001, and only 6% of BIS1 values were >46.ConclusionPatients who awakened early had higher BIS values after the first dose of NMB. Processed EEG values after cardiac arrest may provide additional information that could assist with determining best treatment.