Electroencephalogram silence ratio for early outcome prognosis in severe head trauma

Objective: To introduce the electroencephalogram silence-ratio (ESR) as a v ariable derived from mathematically processed electroencephalogram for earl y outcome prognosis in patients with severe head trauma and to comparativel y assess sensitivity, specificity and predictive value vs. somatosensory ev oked potentials and brainstem auditory evoked potentials. Design: Prospective, Interventional study. Setting: Intensive care unit of a university hospital. Patients: A total of 32 adults with severe acute head trauma (Glasgow Coma Scale score less than or equal to 8). Methods and Main Results: In all patients, electroencephalographic recordin g was continuously performed by frontomastoid electrode montage for 24-96 h rs after admission to the ICU. The data were subsequently computed by fast Fourier analysis and the ESR (intervals of suppression as periods >240 msec s during which the electroencephalographic voltage did not exceed 5 mu V) w as displayed and recorded an a computer for further evaluation. Somatosenso ry evoked potentials and brainstem auditory evoked potentials were elicited during the first 2 days after admission. Outcome evaluation was performed 6 months after trauma using the Glasgow Outcome Scale and the Rappaport Dis ability Rating Scale. After careful artifact exclusion, the ESR depicted th e highest sensitivity, specificity, and positive predictive value compared with evoked potentials. Even a highly significant correlation between outco me and ESR was found (p < .0001). Conclusion: The ESR is a valuable variable showing a high reliability with respect to outcome prediction in severe head trauma with a higher predictiv e value than short latency somatosensory evoked potentials. Evidence exists that the ESR provides at least partial information regarding adequate cere bral oxygen delivery.