Prognostic Value of P25/30 Cortical Somatosensory Evoked Potential Amplitude After Cardiac Arrest*

Abstract

Objectives: The aim of this study was to evaluate the prognostic performance of the peak amplitude of P25/30 cortical somatosensory evoked potentials in predicting nonawakening in targeted temperature management-treated cardiac arrest patients. Design: Prospective analysis. Setting: Four academic tertiary care hospitals. Patients: Eighty-seven cardiac arrest survivors after targeted temperature management. Interventions: Analysis of the amplitude of P25/30. Measurements and Main Results: In all participants, somatosensory evoked potentials were recorded after rewarming, and bilaterally absent pupillary and corneal reflexes were evaluated at 72 hours after the return of spontaneous circulation. We analyzed the amplitudes of the N20 and P25/30 peaks and the N20–P25/30 complex in cortical somatosensory evoked potentials. Upon hospital discharge, 87 patients were dichotomized into the awakening and nonawakening groups. The lowest amplitudes of N20, P25/30, and N20–P25/30 in the awakening patients were 0.17, 0.45, and 0.73 μV, respectively, and these thresholds showed a sensitivity of 70.5% (95% CI, 54.8–83.2%), 86.4% (95% CI, 72.7–94.8%), and 75.0% (95% CI, 59.7–86.8%), respectively, for nonawakening. The area under the curve of the P25/30 amplitude was significantly higher than that of the N20 amplitude (0.955 [95% CI, 0.912–0.998] vs 0.894 [95% CI, 0.819–0.969]; p = 0.036) and was comparable with that of the N20–P25/30 amplitude (0.931 [95% CI, 0.873–0.989]). Additionally, adding resuscitation variables or an absent brainstem reflex to the P25/30 amplitude showed a trend toward improving prognostic performance compared with the use of other somatosensory evoked potential amplitudes (area under the curve, 0.958; 95% CI, 0.917–0.999 and area under the curve, 0.974; 95% CI, 0.914–0.996, respectively). Conclusions: Our results provide evidence that the absence of the P25/30 peak and a reduction in the P25/30 amplitude may be considered prognostic indicators in these patients.

Early Latency Somatosensory Evoked Potentials Are Considered Robust Tests That Are Relatively Insensitive to Some Confounders After Cardiac Arrest That Received Targeted Temperature Management: Today We Are Not Sure Anymore!

“…They conclude that their results “indicate that a P25/30 amplitude less than 0.45 µV is a reliable threshold below which no patients recover consciousness.” We would like to comment. Whereas the results by Oh et al (1) are interesting and call for further investigation of the benefits of their strategy, their conclusion stating a 100% specificity seems currently unwarranted. Although the false positive rate (FPR) of absent early cortical SSEP for predicting poor outcome has usually been estimated to be within the 0.4–0.7% range (2), a recent reevaluation of this value rose the estimated FPR to an alarming 7.7% by taking the “self-fulfilling prophecy” (SPF) bias into account (2).…”

“…We have read with great interest the article published in a recent issue of Critical Care Medicine by Oh et al (1) who conclude that currently somatosensory evoked potentials (SSEPs) are considered robust tests that are relatively insensitive to some confounders after cardiac arrest who received targeted temperature management (1). Elaborating their strategy on previous work shows that all patients showing low (< 0.62 µV) N20-P25/30 amplitudes had poor outcomes, they focused on baseline-to-P25/30 amplitudes, considered to be less prone to bias due to suboptimal electrode positioning (1). By resorting to that strategy, they obtained an improved (86.4%) sensitivity of abnormal early SSEP for predicting poor outcome, without compromising specificity.…”

“…By prognosticating poor outcome, the SSEP results contribute to prompt withdrawal of life-supporting therapies (WLSTs), thus biasing its predictive value close to 100%. Oh et al (1) reckon that their study was not immune to the SPF effect. With a sample size of 44 patients showing an FPR count of zero, the study by Oh et al (1) was at significant risk of missing the true value.…”

“…Oh et al (1) reckon that their study was not immune to the SPF effect. With a sample size of 44 patients showing an FPR count of zero, the study by Oh et al (1) was at significant risk of missing the true value. It has been calculated that even with a genuine FPR as high as 5% and no WLST bias, such a sample size could lead to a 10% probability that all outcomes were poor (2).…”

2020 Korean Guidelines for Cardiopulmonary Resuscitation. Part 5. Post-cardiac arrest care

“…In 21 studies, when bilateral absence of N20 waves was observed in the SSEP conducted at 24 hours or more after ROSC, a poor neurological outcome was predicted with specificity of 50% to 100% and sensitivity of 18.2% to 70.5%. 101,102,114,121,123,127,128,134,[144][145][146][147][148][149][150][151][152][153][154][155][156] Although decrease in the amplitude of N20 is associated with a poor neurological outcome in some studies, further studies are needed. 152,155,157,158 Since there is a high likelihood that results are affected by confounding factors within 24 hours after ROSC, it is recommended to use bilateral absence of N20 waves more than 24 hours after ROSC in combination with other prognostic tests.…”