Somatosensory evoked potential changes in position-related brain stem ischemia

The park bench or three-quarters prone position has been advocated because of the low incidence of air emboli and the advantage of cerebellar displacement away from the brain stem by gravity. An integral part of that position is flexion and rotation of the head to optimize exposure and minimize venous bleeding. A patient is described in whom probable brain stem ischemia was demonstrated by somatosensory evoked potential monitoring despite technically correct park bench positioning and normal arterial blood pressure, intracranial pressure, and cerebral perfusion pressure.