Predictors of poor neurological outcome in adult comatose survivors of cardiac arrest: a systematic review and meta-analysis. Part 2: Patients treated with therapeutic hypothermia.

AIMS AND METHODS: To systematically review the accuracy of early (≤7 days) predictors of poor outcome, defined as death or vegetative state (Cerebral Performance Categories [CPC] 4-5) or death, vegetative state or severe disability (CPC 3-5), in comatose adult survivors from cardiac arrest (CA) treated using therapeutic hypothermia (TH). Electronic databases were searched for eligible studies. Sensitivity, specificity, and false positive rates (FPR) for each predictor were calculated. Quality of evidence (QOE) was evaluated according to the GRADE guidelines.

RESULTS: 37 studies (2403 patients) were included. A bilaterally absent N20 SSEP wave during TH (4 studies; QOE: Moderate) or after rewarming (5 studies; QOE: Low), a nonreactive EEG background (3 studies; QOE: Low) after rewarming, a combination of absent pupillary light and corneal reflexes plus a motor response no better than extension (M≤2) (1 study; QOE: Very low) after rewarming predicted CPC 3-5 with 0% FPR and narrow (<10%) 95% confidence intervals. No consistent threshold for 0% FPR could be identified for blood levels of biomarkers. In 6/8 studies on SSEP, in 1/3 studies on EEG reactivity and in the single study on clinical examination the investigated predictor was used for decisions to withdraw treatment, causing the risk of a self-fulfilling prophecy.

CONCLUSIONS: in the first 7 days after CA, a bilaterally absent N20 SSEP wave anytime, a nonreactive EEG after rewarming or a combination of absent ocular reflexes and M≤2 after rewarming predicted CPC 3-5 with 0% FPR and narrow 95% CIs, but with a high risk of bias.