Do changes in SSEP amplitude over time predict the outcome of comatose survivors of cardiac arrest?

AIM: To assess if the amplitude of the N20 wave (N20Amp) of somatosensory evoked potentials (SSEPs) changes between 12-24h and 72h from the return of spontaneous circulation (ROSC) after cardiac arrest and if an N20Amp decrease predicts poor neurological outcome (CPC 3-5) at six months. Setting retrospective analysis of the ProNeCA multicentre prognostication study dataset. (NCT03849911).

METHODS: In adult comatose cardiac arrest survivors whose SSEPs were recorded at both 12-24h and 72h after ROSC, we measured the median N20Amp at each timepoint and the individual change in N20Amp across the two timepoints. We identified their cutoffs for predicting poor outcome with 0% false positive rate (FPR) and compared their sensitivities.

RESULTS: We included 236 patients. The median [IQR] N20Amp increased from 1.90 [0.78-4.22] µV to 2.86 [1.52-5.10] µV between 12-24h and 72h (p = 0.0019). The N20Amp cutoff for 0% FPR increased from 0.6 µV at 12-24h to 1.23 µV at 72h, and its sensitivity increased from 56[48-64]% to 71[63-77]%. Between 12-24h and 72h, an N20Amp decrease >53% predicted poor outcome with 0[0-5]% FPR and 26[19-35]% sensitivity. Its combination with an N20Amp<1.23µV at 72h increased sensitivity by 1% to 72[64-79]%.

CONCLUSION: In comatose cardiac arrest survivors, the median N20Amp and its cutoff for predicting poor neurological outcome increase between 12-24 and 72h after ROSC. An N20Amp decrease greater than 53% between these two timepoints predicts poor outcome with 0% FPR, confirming the unfavourable prognostic signal of a low N20Amp at 72h.