Electropyhsiological assessment of the afferent sensory pathway in cardiac arrest survivors

Background Hypoxic-ischaemic brain damage in cardiac arrest survivors is global, but postmortem histology could identify parts of the brain that are selectively vulnerable to ischaemia, comprising the thalamus and cortex. We hypothesized that hypoxic-ischaemic brain damage increases along the afferent sensory pathway with a stepwise decrease of detectable somatosensory evoked potential peaks. Methods Somatosensory evoked potentials were recorded within 72 h after cardiac arrest in 305 comatose patients after cardiopulmonary resuscitation. We measured the short latency SEP peaks N9, P15, N20, P25 (reflecting the peripheral-thalamo-cortical pathway) and the long latency SEP peaks N35 and N70 (reflecting complex cortico-cortical interactions). Patients with a Cerebral Performance Category score > 2 at 1 year were defined as patients with hypoxic-ischaemic brain damage. Results Patients with hypoxic-ischaemic brain damage (n = 232) showed a statistically significant decrease of detectable peaks (P < 0.05) along the thalamo-cortical afferent pathway: N13, P15, N20, P25 and N70 peaks were detectable in 99%, 63%, 59%, 55% and 44% patients, respectively. In patients without hypoxic-ischaemic brain damage (n = 73) the N13, P15, N20, P25 peaks were detectable in all, and the N35 and N70 peaks in 98%. Furthermore, in patients with hypoxic-ischaemic brain damage and detectable SEP peaks, P15, N20, P25, N35 and N70, peak latencies were prolonged (P < 0.05) and N20 and N70 amplitudes were decreased (P < 0.05) compared with patients without hypoxic-ischaemic brain damage. Conclusion Extent of hypoxic-ischaemic brain damage in cardiac arrest survivors increases along the afferent sensory pathway, with pronounced vulnerability of thalamic and cortical brain regions.