This recording demonstrates somatosensory-evoked potentials recorded after stimulation of the left and right median nerves in a 38-yr-old male with hypoxic–ischemic encephalopathy attributable to cardiac arrest of prolonged duration. Note that there are robust signals from recording electrodes at the axilla, C5 spinous process, and the mastoid (brainstem activity). There is, however, no response at all from cortical electrodes placed on the scalp.
Somatosensory-evoked potentials have been in common clinical use since the 1980s. They are commonly used for intraoperative monitoring, diagnosis of central nervous system pathology (e.g., multiple sclerosis), and, in some cases, peripheral nerve or root disease. When stimulating mixed nerves, one can often record from multiple sites as the depolarization proceeds rostrally up the nervous system.
Regarding this case, multiple studies in the literature have demonstrated that no patients in this setting awaken from coma when cortical responses are absent bilaterally. Given the numbers of individuals who have been studied, the 95% confidence indicates that there is less than a 1% chance of awakening.1,2 This is judged by many as representing medical futility.3 Hence, soon after onset of coma, the patient care team and family may want to discuss discontinuing life support.
In traumatic coma, the situation is somewhat different. About 5% of such individuals awaken, but most of these would have severe disability. In children with coma, about 7% of individuals awaken, and many of these have a good outcome.1 Thus, the results demonstrated above are of the most use in those with hypoxic–ischemic encephalopathy (Fig. 1).
In this case, the patient’s family agreed to have life support withdrawn, and brain death was pronounced shortly thereafter.
1. Robinson LR, Micklesen PJ, Tirschwell DL, Lew HL: Predictive value of somatosensory evoked potentials for awakening from coma. Crit Care Med
2. Zandbergen EG, Hijdra A, Koelman JH, et al: Prediction of poor outcome within the first 3 days of postanoxic coma. Neurology
3. Schneiderman LJ, Jecker NS, Jonsen AR: Medical futility: its meaning and ethical implications. Ann Intern Med