Association of the Bedside Shivering Assessment Scale and derived EMG power during therapeutic hypothermia in survivors of cardiac arrest

Abstract

Introduction Shivering during therapeutic hypothermia (TH) after cardiac arrest (CA) is common, but the optimal means of detection and appropriate threshold for treatment are not established. In an effort to develop a quantitative, continuous tool to measure shivering, we hypothesized that continuous derived electromyography (dEMG) power detected by the Aspect A2000 or VISTA monitor would correlate with the intermittent Bedside Shivering Assessment Scale (BSAS) performed by nurses. Methods Among 38 patients treated with TH after CA, 853 hourly BSAS measurements were compared to dEMG power measured every minute by a frontal surface electrode. Patients received intermittent vecuronium by protocol to treat clinically recognized shivering (BSAS > 0). Mean dEMG power in decibels (dB) was determined for the hour preceding each BSAS measurement. dEMG and BSAS were compared using ANOVA. Results The median dEMG power for a BSAS score of 0 (no shivering) was 27 dB (IQR 26–31 dB), BSAS 1 was 30.5 dB (IQR 28–35 dB), BSAS 2 was 34 dB (IQR 30–38 dB), and BSAS 3 was 34.5 dB (IQR 32–44.25). The dEMG for BSAS ≥ 1 (shivering) was statistically different from BSAS 0 ( p < 0.0001). dEMG and BSAS correlated moderately ( r = 0.66, p < 0.001). Conclusion dEMG power measured from the forehead with the Aspect A2000 or VISTA monitor during therapeutic hypothermia correlated with the Bedside Shivering Assessment Scale. Given its continuous trending of dEMG power, the A2000 or VISTA may be a useful research and clinical tool for objectively monitoring shivering.