Abstract
BackgroundWe 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.MethodsUsing 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.ResultsA 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).ConclusionsThe 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.
Highlights
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
OHCA out-of-hospital cardiac arrest, CPR cardiopulmonary resuscitation, ROSC return of spontaneous circulation, SD standard deviation, SSEP somatosensory evoked potential, IQR interquartile range, CPC Cerebral Performance Category an area under the receiver operating characteristic (ROC) curve (AUC) of 0.65, 0.85, and 0.86, respectively (Fig. 5)
The AUCs increased when the absence of P25 or N20–P25 amplitude was added (AUC 0.95 and AUC 0.97, respectively), and the differences were statistically significant (Additional file 3: Table S1). In this retrospective, single-center registry-based study, when we focused on the P25 peak or N20–P25 component, the sensitivity for predicting a poor outcome and the specificity for predicting a good outcome simultaneously increased more than twofold compared to those of the traditionally used pattern
Summary
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. These confounders might limit the value of a neurological examination and necessitate other multimodal prognostic approaches Of these modalities, somatosensory evoked potential (SSEP) measurement is a noninvasive bedside technique that can even be used for unstable critically ill patients and is less confounded by sedation or hypothermia than electroencephalography (EEG). High noise levels and artifacts may affect the ability to discern a low-amplitude N20 and impede reliable interpretation [8]. These problems could produce interobserver disagreement and false-positive cases. Endisch et al performed a large prospective study on the relationship between cortical SSEP amplitudes and short-term neurological outcomes and found that absent or very low-amplitude SSEPs appear to be highly predictive of a poor outcome, with high sensitivity [17]. Kim et al reported that the absence of P25/30 has better sensitivity than the absence of N20 for predicting a poor neurological outcome at hospital discharge [18]
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