S25. Prognostic value of N20 amplitude in patients with postanoxic coma

Abstract

Bilateral absence of cortical N20 responses of median nerve somatosensory evoked potentials (SEP) is a reliable predictor of poor neurological outcome in postanoxic coma after cardiopulmonary resuscitation. However the preservation of N20 does not prognosticate awakening, in fact is an uncertain pattern. The prognostic value of N20 amplitude has still not been sufficiently documented. In our knowledge only one study has analyzed N20 amplitude. The aim of this study was to review the relationship between N20 amplitude and neurological outcome in our postanoxic patients. We retrospectively review the data of all our patients who remained comatose after cardiopulmonary resuscitation between 2013 and 2017. The following variables were collected: N20 amplitude, clinical examination, EEG data, neuron-specific enolase and outcome determined upon hospital discharge by means of Cerebral performance category (CPC). The patients with CPC 1–3 were defined as good outcome, and those with CPC 4–5 as poor outcome. We identified 76 postanoxic patients with N20 present. Fifty-three (69.7%) had poor outcome (CPC 4–5). The mean N20 amplitude in these patients was 1.90 μV (SD 2.01 range 0.16–7.9). Twenty-three patients (30.2%) had good outcome (CPC 1–3) and the mean N20 amplitude in these patients was 3.43 μV (SD 2.73 range 0.93–11.3). The ROC curve shows 0.86 μV as the cut-value for a better specificity with higher sensitivity. Any patient with amplitude lowest than 0.86 μV had good outcome (specificity 100%, sensitivity 50.9%, positive predictive value 100%, negative predictive value 46.9%). In our postanoxic patients very low N20 amplitudes appear to be highly predictive of poor outcome. Our results corroborate published data.