A lot has changed since the seminal paper by Levy et al. in JAMA neurology in 1985. The advent of therapeutic hypothermia (TH) has introduced uncertainty in prognostication. Cahill et al. reviewed in 2014 the most commonly used prognostic markers (physical examination, myoclonus, EEG, somatosensory evoked potentials SSEP, biochemical markers, and neuroimaging) in the era of therapeutic hypothermia. Dr. Maciel (joining UF faculty this summer), Dr. Youn, and colleagues have recently published an article titled “SSEP in therapeutic hypthermia era” in the Journal of Clinical Neurophysiology.
They conducted a retrospective assessment of the N20 responses in cardiac arrest survivors treated with TH. 73 patients with 93 SSEP studies (44 studies during TH) were reviewed. 11 of the 44 SSEP performed in TH had absent N20 peaks. Only 3 of the 11 had a repeat SSEP in normothermia which showed the persistent absence of N20 peaks. Despite the limitations of a small cohort, “the positive predictive value of SSEP in predicting nonawakening from hypoxic-ischemic encephalopathy in patients treated with TH was 100%”. They conclude that SSEP can still be considered for prognostication in the TH era. Factors that can affect SSEP include the cooling process (recommend waiting 48 hours from euthermia) and the effects of sedatives. They encourage multimodal prognostication and urge against “early perssimistic prognostication”.