Estimating the False Positive Rate of Absent Somatosensory Evoked Potentials in Cardiac Arrest Prognostication

Abstract

Objective: Absence of short-latency cortical median nerve somatosensory evoked potentials (“absent SSEPs”) is considered a nearly perfect predictor of poor outcome after cardiac arrest. However, reports of good outcomes despite absent SSEPs and high rates of withdrawal of life-sustaining therapies (WLST) have raised concerns that estimates of the prognostic value of absent SSEPs may be biased by self-fulfilling prophecies. We aimed to develop an unbiased estimate of the false positive rate (FPR) of absent SSEPs as a predictor of poor outcome after cardiac arrest. Data Sources: PubMed. Study Selection: We selected 35 studies in cardiac arrest prognostication that reported SSEP results. Data Extraction: In each study, we identified rates of WLST and good outcomes despite absent SSEPs. We appraised studies for potential biases using the Quality in Prognostic Studies tool. Using these data, we developed a statistical model to estimate the FPR of absent SSEPs adjusted for WLST rate. Data Synthesis: Two thousand, one hundred and thirty-three subjects underwent SSEP testing. Five hundred and ninety-four had absent SSEPs; of these,14 had good functional outcomes. The rate of WLST for subjects with absent SSEP could be estimated in 14 of the 35 studies (mean 80%, median 100%). The FPR for absent SSEP in predicting poor neurologic outcome, adjusted for a WLST rate of 80%, is 7.7% (95% Confidence Interval: 4–13%). Conclusions: Absent cortical SSEPs do not infallibly predict poor outcome in patients with coma following cardiac arrest. The chances of survival in subjects with absent SSEPs, though low, may be substantially higher than generally believed.

Performance of a guideline-recommended algorithm for prognostication of poor neurological outcome after cardiac arrest

“…As supported by our results, false positive findings may occur with all methods currently used for prognostication, emphasizing the importance of a multimodal approach to reduce the risk of overly pessimistic predictions [8,[23][24][25][26]. Six patients with single pathological findings were awake and obeying commands on day 4, illustrating that sufficient time for recovery post-arrest is also an important part of neurological prognostication [1,27].…”

“…Bilaterally absent N20-potentials in combination with early status myoclonus or in isolation were considered predictive of poor outcome in the TTM-trial. Whilst SSEP is considered a very robust method for prognostication after cardiac arrest, the self-fulfilling prophecy may have affected most previous studies [ 25 , 28 , 29 ]. One patient with absent N20-potentials in the TTM-trial awoke before scheduled prognostication [ 11 ] and the majority of our patients lacking N20 potentials had ≥ 1 additional prognostic finding indicating severe brain injury.…”

Relevance of Somatosensory Evoked Potential Amplitude After Cardiac Arrest

“…Second, a potential problem in unblinded studies investigating diagnostic accuracy is the self-fulfilling prophecy. This characterizes almost all studies on this topic (27). Although EEG classifications were assigned offline, and treatment withdrawal was never based on the EEG or low SSEP amplitude, attending physicians were not blinded for the SSEP outcome.…”

Recovery from disorders of consciousness: mechanisms, prognosis and emerging therapies

“…Evoked potentials can be used to assess the integrity of specific sensory pathways, that is, the transmission of tactile sensation to the somatosensory cortex, providing reliable information about the overall impact of diffuse brain injury. For example, measurement of somatosensory evoked potentials are frequently used to aid prognostication following cardiac arrest 154 and TBI 155 — the absence of a negative potential 20 ms after peripheral stimulation reflects loss of thalamocortical integrity.…”