Background: Bilateral absent N20 responses of median nerve somatosensory evoked potentials (SEPs) reliably predict poor prognosis after cardiac arrest. However, the studies supporting this fact were carried out before hypothermia was established as standard treatment. Recent evidence suggests that hypothermia treatment affects the predictive value of clinical findings in cardiac arrest patients, raising the question whether the predictive value of N20 responses has changed as well. Methods: We retrospectively studied 185 consecutive patients treated with hypothermia after cardiac arrest. SEP recordings were available for 112 patients. SEPs were classified as bilateral absent N20, pathologic N20, or normal. Baseline and follow-up information were obtained from our database. Results: We identified 36 patients with bilateral absent N20, 35 (97%) of whom had poor outcome. One patient had prolonged high amplitude peripheral SEP, but bilaterally absent N20 3 days after cardiac arrest and regained consciousness with normal cognitive functions and reproducible N20 responses. One further patient had minimally detectable N20 at day 3 and recovered consciousness and normal N20 responses on follow-up. Conclusions: Our data indicate that recovery of consciousness and cognitive functions is possible in spite of absent or minimally present N20 responses more than 24 hours after cardiac arrest in a very small proportion of patients. N20 responses may recover beyond this time window. The predictive value of bilateral absent N20 responses needs to be reevaluated in larger prospective studies. Until these studies are available, decisions to stop therapy in cardiac arrest survivors should not be based on N20 responses alone.

Introduction: Neuron specific enolase (NSE) has been proven effective in predicting neurological outcome after cardiac arrest with a current cut off recommendation of 33 μg/l. However, most of the corresponding studies were conducted before the introduction of mild therapeutic hypothermia (MTH). Therefore we conducted a study investigating the association between NSE and neurological outcome in patients treated with MTH Methods: In this prospective observational cohort study the data of patients after cardiac arrest receiving MTH (n = 97) were consecutively collected and compared with a retrospective non-hypothermia (NH) group (n = 133). Serum NSE was measured 72 hours after admission to ICU. Neurological outcome was classified according to the Pittsburgh cerebral performance category (CPC 1 to 5) at ICU discharge. Results: NSE serum levels were significantly lower under MTH compared to NH in univariate analysis. However, in a linear regression model NSE was affected significantly by time to return of spontaneous circulation (ROSC) and ventricular fibrillation rhythm but not by MTH. The model for neurological outcome identified NSE, NSE*MTH (interaction) as well as time to ROSC as significant predictors. Receiver Operating Characteristic (ROC) analysis revealed a higher cutoff value for unfavourable outcome (CPC 3 to 5) with a specificity of 100% in the hypothermia group (78.9 μg/l) compared to the NH group (26.9 μg/l). Conclusions: Recommended cutoff levels for NSE 72 hours after ROSC do not reliably predict poor neurological outcome in cardiac arrest patients treated with MTH. Prospective multicentre trials are required to re-evaluate NSE cutoff values for the prediction of neurological outcome in patients treated with MTH.

Anatomical studies in monkeys, and functional imaging and lesion studies in humans, suggest that, within the primate medial temporal neocortex, the parahippocampal cortex (PHC) is particularly involved in spatial tasks. However, evidence for a functional specialization of the PHC regarding its spatial memory functions has so far been lacking. Here, we investigated spatial memory functions of the human perirhinal cortex (PRC) and PHC. Patients with lesions affecting the PRC but sparing the PHC, and patients with lesions affecting both PRC and PHC, performed an oculomotor delayed response task with unpredictably varied memory delays of up to 30 s. Compared to controls, patients with PRC+PHC lesions showed a significant delay-dependent inaccuracy of memory-guided eye movements contralateral to the lesion side, whereas patients with PRC lesions showed no significant inaccuracy. Our results show that the PHC is a critical component for spatial memory in humans and suggest that (i) extrahippocampal spatial memory functions of the medial temporal lobe may not be equally distributed in the medial temporal neocortex, but may be largely confined to the PHC, and (ii) damage to connections between cortices involved in spatial cognition and rostral regions of the temporal lobe is unlikely to account for the observed spatial memory deficits with PHC lesions.

Mild therapeutic hypothermia alters the validity of a number of parameters currently used to predict neurological outcome after cardiac arrest and resuscitation. Thus, additional parameters are needed to increase certainty of early prognosis in these patients. A promising new approach is the determination of the gray-white-matter ratio (GWR) in cranial computed tomography (CCT) obtained early after resuscitation. It is not known how GWR relates to established outcome parameters such as neuron specific enolase (NSE) or somatosensory evoked potentials (SSEP).