Biochemical markers and somatosensory evoked potentials in patients after cardiac arrest: the role of neurological outcome scores

Biochemical markers, e.g. NSE or S100B, and somatosensory evoked potentials (SSEP) are considered promising candidates for neurological prognostic predictors in patients after cardiac arrest (CA). The Utstein Templates recommend the use of the Glasgow-Pittsburgh Cerebral Performance Categories (GP-CPC) to divide patients according to their neurological outcome. However, several studies investigating biochemical markers and SSEP are based on the Glasgow Outcome Score (GOS). We noticed that many studies failed to exclude patients who died without certified brain damage from patients classified as poor outcome, instead including all patients who died into this category. Therefore, we summarized the published NSE cut-off values and the derived sensitivity and specificity to predict poor outcome of those studies which only included patients with certified brain death in GOS-1 or GP-CPC-5 (group A) vs. those studies which did not differentiate between death from any cause or death due to primary brain damage (group B). On average, mean NSE cut-off values and sensitivity were higher (56 ± 35 ng/ml, 56 ± 18%) in group A than in group B (41 ± 17 ng/ml, 44 ± 25%), respectively. The specificity remained equally high in both groups. In analogy, the average sensitivity of SSEP to predict poor outcome was higher in group A (76 ± 11%) than in group B (50 ± 15%), while the specificity was similar in both groups. Conclusively, inclusion of deaths without certified brain damage after CA in neurological outcome studies will lead to underestimation of the prognostic power of biochemical or electrophysiological markers for brain damage. A modified GOS and GP-CPC score might help to avoid this bias.