Introduction: Therapeutic hypothermia (TH) has raised questions about the ability to accurately prognosticate after cardiac arrest (CA). The purpose of this study was to determine the association between previously established predictors of outcome after cardiac arrest in patients treated with therapeutic hypothermia.
Methods: We retrospectively reviewed all survivors of CA (in or out-of-hospital) with any initial rhythm from 2006 - 2012. Predictors of interest included SSEP N20 potentials (present or absent), EEG (suppression-burst (S-B) or GPEDs versus other patterns), NSE levels (> or < 33ng/ml), clinical exam findings on Glasgow Coma Scale (GCS) and pupil reactivity days 1-3 post-CA. Clinical outcomes at the time of hospital discharge were dichotomized by Cerebral Pittsburgh Performance Category (CPC) with good outcome CPC = 1-2, and poor outcome CPC=3-5. Variables were analyzed by Fisher's exact test and by single-variable logistic regression.
Results: We analyzed 77 patients who were treated with TH. We found statistically significant evidence (P value <0.05) of association with good outcome for pupillary light reactivity on day 1 (OR=5.0, 95% CI: 1.05-23.9) and day 3 (P=0.008), GCS motor ≥ 4 day 1 (OR=3.5, 95%CI: 1.1-11.4) and 3 (P=0.001), day 3 GCS total score ≥ 8 (OR=32, 95% CI: 4.0 - 258.8), SSEP present N20 (P=0.02), NSE < 33 (P=0.02). Sensitivity and specificity of SSEP absent N20 potentials whether measured in the hypothermic period or not was 100% and 53%, NSE was 87% and 47%, and EEG S-B/GPED was 100% and 30% respectively.
Conclusion: These results suggest that preserved pupil light reactivity, GCS motor subscore ≥ 4 on days 1 and 3, present N20 potentials on SSEP, and NSE < 33 are associated with good neurological outcome at the time of hospital discharge in patients treated with TH. SSEP also appeared valid for predicting poor outcome when N20 potentials were absent even during hypothermia.