Beyond dichotomy: patterns and amplitudes of SSEPs and neurological outcomes after cardiac arrest

We hypothesized that the absence of P25 and the N20-P25 amplitude in somatosensory evoked potentials (SSEPs) have higher sensitivity than the absence of N20 for poor neurological outcomes, and we evaluated the ability of SSEPs to predict long-term outcomes using pattern and amplitude analyses.

Using prospectively collected therapeutic hypothermia registry data, we evaluated whether cortical SSEPs contained a negative or positive short-latency wave (N20 or P25). The N20-P25 amplitude was defined as the largest difference in amplitude between the N20 and P25 peaks. A good or poor outcome was defined as a Glasgow-Pittsburgh Cerebral Performance Category (CPC) score of 1-2 or 3-5, respectively, 6 months after cardiac arrest.

A total of 192 SSEP recordings were included. In all patients with a good outcome (n = 51), both N20 and P25 were present. Compared to the absence of N20, the absence of N20-P25 component improved the sensitivity for predicting a poor outcome from 30.5% (95% confidence interval [CI], 23.0-38.8%) to 71.6% (95% CI, 63.4-78.9%), while maintaining a specificity of 100% (93.0-100.0%). Using an amplitude < 0.64 μV, i.e., the lowest N20-P25 amplitude in the good outcome group, as the threshold, the sensitivity for predicting a poor neurological outcome was 74.5% (95% CI, 66.5-81.4%). Using the highest N20-P25 amplitude in the CPC 4 group (2.31 μV) as the threshold for predicting a good outcome, the sensitivity and specificity were 52.9% (95% CI, 38.5-67.1%) and 96.5% (95% CI, 91.9-98.8%), respectively. The predictive performance of the N20-P25 amplitude was good, with an area under the receiver operating characteristic curve (AUC) of 0.94 (95% CI, 0.90-0.97). The absence of N20 was statistically inferior regarding outcome prediction (p < 0.05), and amplitude analysis yielded significantly higher AUC values than did the pattern analysis (p < 0.05).

The simple pattern analysis of whether the N20-P25 component was present had a sensitivity comparable to that of the N20-P25 amplitude for predicting a poor outcome. Amplitude analysis was also capable of predicting a good outcome.