Abstracts

Rationale: In anoxic brain injury, a lack of thalamocortical components (N19/P22) on somatosensory evoked potentials (SSEPs) is 100% specific for a poor outcome and has proven to be a better predictor than a malignant electroencephalogram (EEG). More recently, postanoxic status epilepticus (PSE) has been found to be an independent predictor of poor outcome in this setting, with rates approaching 100% mortality. Previous studies have not specifically looked at the correlation of PSE and SSEP findings. The purpose of the current study was to assess the correlation of SSEP and PSE findings in patients with anoxic brain injury, and to assess the reliability of SSEP in the presence of PSE. Methods: We reviewed all patients at the Massachusetts General Hospital, from 2004-2008, that had at least one SSEP and one EEG after a diagnosis of anoxic brain injury. Demographic data was collected including age, gener, cause of anoxia, treatments and co-morbidities. The SSEPs were reviewed based on the thalamocortical components (N19/P22), and were classified as normal, low amplitude, or absent (with preserved cervico-medullary junction potentials). EEGs were classified in only two categories, slow and PSE. Overall patient outcomes were recorded. Results: Thiry-one patients were included in the study. Thirteen patients had PSE on EEG. In this subgroup, twelve patients had primary cardiac arrest, while one had a primary respiratory arrest with subsequent pulseless electrical activity. Eight patients received cooling. Six patients had a normal SSEP, six had an absent SSEP, and one had a peripheral nerve conduction defect. All but one patient had active care withdrawn and died. The one patient had an outome of persistent vegetative state, N19/P22 were absent. Conclusions: This small restrospective study shows that a large proportion of patients, in our case 6/13, who have PSE on EEG, will have a normal SSEP. As has been previously established, a normal SSEP does not imply a good prognosis, but our experience here shows that PSE on an EEG does not preclude registration of a normal appearing N19/P22 and attests to the reliability of these waveforms in a problematic setting. PSE itself is a somewhat controversial entity, in that some feel it does not represent typical, clinically correlated, status epilepticus requiring treatment. However, studies are currently underway to assess outcome after anoxic brain injury with aggressive treatment of this EEG pattern. We propose that normal SSEPs, in the presence of PSE, be a minimal criteria for treatment, even in study settings. In addition, absent SSEPS should serve as an endpoint of treatment in this setting.