The prognostic value of bispectral index and suppression ratio monitoring after out-of-hospital cardiac arrest: a prospective observational study

Ward Eertmans, Cornelia Genbrugge, Margot Vander Laenen, Willem Boer, Dieter Mesotten, Jo Dens, Frank Jans, Cathy De Deyne

We investigated the ability of bispectral index (BIS) monitoring to predict poor neurological outcome in out-of-hospital cardiac arrest (OHCA) patients fully treated according to guidelines. In this prospective, observational study, 77 successfully resuscitated OHCA patients were enrolled in whom BIS, suppression ratio (SR) and electromyographic (EMG) values were continuously monitored during the first 36 h after the initiation of targeted temperature management at 33 °C. The Cerebral Performance Category (CPC) scale was used to define patients' outcome at 180 days after OHCA (CPC 1-2: good-CPC 3-5: poor neurological outcome). Using mean BIS and SR values calculated per hour, receiver operator characteristics curves were constructed to determine the optimal time point and threshold to predict poor neurological outcome. At 180 days post-cardiac arrest, 39 patients (51%) had a poor neurological outcome. A mean BIS value ≤ 25 at hour 12 predicted poor neurological outcome with a sensitivity of 49% (95% CI 30-65%), a specificity of 97% (95% CI 85-100%) and false positive rate (FPR) of 6% (95% CI 0-29%) [AUC: 0.722 (0.570-0.875); p = 0.006]. A mean SR value ≥ 3 at hour 23 predicted poor neurological with a sensitivity of 74% (95% CI 56-87%), a specificity of 92% (95% CI 78-98%) and FPR of 11% (95% CI 3-29%) [AUC: 0.836 (0.717-0.955); p < 0.001]. No relationship was found between mean EMG and BIS < 25 (R2 = 0.004; p = 0.209). This study found that mean BIS ≤ 25 at hour 12 and mean SR ≥ 3 at hour 23 might be used to predict poor neurological outcome in an OHCA population with a presumed cardiac cause. Since no correlation was observed between EMG and BIS < 25, our calculated BIS threshold might assist with poor outcome prognostication following OHCA.