Somatosensory evoked potentials during mild hypothermia after cardiopulmonary resuscitation

In patients who remain in a coma after cardiopulmonary resuscitation (CPR), the bilateral absence of cortical N20 responses of median nerve somatosensory evoked potentials (SSEP) 24 hours after admission invariably correlates with a poor neurologic outcome. Nowadays, CPR patients are treated with mild hypothermia, with simultaneously administered sedative drugs, hampering clinical neurologic assessment. We investigated whether SSEP performed during hypothermia can reliably predict a poor neurologic outcome.

Between July 2006 and April 2008, this multicenter prospective cohort study included adult comatose patients admitted after CPR and treated with induced mild hypothermia (32-34 degrees C). SSEP was performed during hypothermia, and in patients who remained comatose after rewarming, a second SSEP was performed. Neurologic outcome was assessed 30 days after admission with the Glasgow Outcome Scale.

Seventy-seven consecutive patients were included in 2 hospitals. In 13 patients (17%), the cortical N20 response during hypothermia was bilaterally absent. In 9 of these 13 patients in whom SSEP could be repeated during normothermia, the N20 response was also absent, yielding a positive predictive value of 1.00 (95% confidence interval [CI] 0.70-1.00). All 13 patients with absent SSEP during hypothermia had a poor neurologic outcome, yielding a positive predictive value of 1.00 (95% CI 0.77-1.00).

The results of this pilot study show that bilaterally absent cortical N20 responses of median nerve somatosensory evoked potentials performed during mild hypothermia after resuscitation can predict a poor neurologic outcome. We started a larger multicenter prospective cohort study to confirm these results.