Objective: Therapeutic hypothermia (TH) is a recommended treatment for survivors of cardiac arrest. Prognostication is complicated since sedation and muscle relaxation are used and established indicators of a poor prognosis are lacking. This prospective, observational study describes the pattern of commonly used prognostic markers in a hypothermia-treated cohort of cardiac arrest patients with prolonged coma.
Methods: Among 111 consecutive patients, 19 died, 58 recovered, and 34 were in coma 3 days after normothermia (4.5 days after cardiac arrest), defined as prolonged coma. All patients were monitored with continuous amplitude-integrated EEG and repeated samples of neuron-specific enolase (NSE) were collected. In patients with prolonged coma, somatosensory evoked potentials (SSEP) and brain MRI were performed. A postmortem brain investigation was undertaken in patients who died.
Results: Six of the 17 patients (35%) with NSE levels <33 μg/L at 48 hours regained the capacity to obey verbal commands. By contrast, all 17 patients with NSE levels >33 failed to recover consciousness. In the >33 NSE group, all 10 studied with MRI had extensive brain injury on diffusion-weighted images, 12/16 lacked cortical responses on SSEP, and all 6 who underwent autopsy had extensive severe histologic damage. NSE levels also correlated with EEG pattern, but less uniformly, since 11/17 with NSE <33 had an electrographic status epilepticus (ESE), only one of whom recovered. A continuous EEG pattern correlated to NSE <33 and awakening.
Conclusions: NSE correlates well with other markers of ischemic brain injury. In patients with no other signs of brain injury, postanoxic ESE may explain a poor outcome.