Postanoxic coma: how (long) should we treat?

Postanoxic coma is a state of unconsciousness caused by global anoxia of the brain, most commonly due to cardiac arrest. Outcome after postanoxic coma lasting more than several hours is generally, but not invariably, poor. Recovery of consciousness reported in the literature varies from 8% to 72% of patients, but is mostly thought to be around 20-30% in patients surviving in coma for at least 24 h. Research is directed at defining factors that reliably predict poor outcome in these patients. Favourable outcome proves impossible to predict. Studies on outcome prediction have focussed mostly on neurological examination, clinical neurophysiological tests and biochemical parameters. The most recent and extensive study in this respect was the PROPAC study in The Netherlands (407 patients). This study confirmed earlier findings that bilaterally absent early cortical response after median nerve somatosensory potentials (absent somatosensory evoked potentials) is the most reliable predictor of poor outcome (no recovery of consciousness). A serum neuron-specific-enolase level >33 microg L(-1) seemed equally reliable. In 2006, the American Practice Parameter on anoxic-ischaemic coma was published, summarizing the findings from the different studies. Poor outcome was defined as death, coma or severe disability after 6 months. The following factors were found to reliably predict this outcome: myoclonic status epilepticus within the first 24 h, absent pupillary responses after 24 h, absent corneal reflexes after 48 h, motor response to pain absent or extensor after 72 h and absent somatosensory evoked potentials (as defined above) after 1-3 days. Results for biochemical parameters (such as neuron-specific enolase) and neuroimaging are inconclusive.