Early-SEPs' amplitude reduction is reliable for poor-outcome prediction after cardiac arrest?

The bilateral absence of cortical Somatosensory Evoked Potentials (SEPs), after cardiac arrest (CA), is a high reliable predictor of poor outcome but it is present in no more than 40% of patients. An amplitude reduction of cortical SEPs was found in about 30% of subjects, but few papers analysed its prognostic significance. The aim of our study is to identify a value of SEP amplitude reduction below which all the CA patients had poor outcome and the relationship between SEP and Electroencephalogram (EEG) patterns.

We analysed comatose patients in whom SEPs and EEG were recorded at 6-12 hours after CA. We evaluated the sensitivity at specificity of 100% of SEP amplitude in predicting the non-recovery of consciousness by plotting Receiver Operating Characteristic (ROC) curves. We also analysed the relationship between SEP amplitude and EEG patterns. Outcome was evaluated at 6 months by Glasgow Outcome Scale.

We analysed 119 subjects. According to the ROC analysis (area under the curve = 0.95/CI 0.91-0.99), all patients with a cortical SEP amplitude <0.65 μV did not recover consciousness (GOS 1-2), with a sensitivity of 71.8%. Severe EEG abnormalities (suppression and burst-suppression patterns) were also observed in all these patients.

Not only the absence but also a bilateral amplitude reduction of cortical SEPs (<0.65 μV) is associated with ominous prognosis (death or non-recovery of consciousness) with a very high predictive value. However, we emphasize that great caution should be applied before adopting amplitude reduction as a criterion for the poor prognosis of CA patients.