P300-mapping--a neurophysiological tool to quantify cerebral dysfunction after coronary artery bypass grafting

Objective parameters are needed to quantify cerebral dysfunction following cardiac surgery in outcome and comparative studies. In this investigation we assessed the value of the late auditory evoked potentials N100 and P300 to measure the neuropsychological deficit after coronary artery bypass grafting (CABG). N100, an exogenous potential is influenced by the stimulus pattern (frequency, intensity and stimulus presentation rate). P300, an endogenous potential, depends on the cognitive processing invoked by the stimulus. With approval of the Human Investigation Committee and the patients' consents, 52 subjects undergoing elective CABG were enrolled. Operation, extracorporal circulation, anesthesia and postoperative intensive care were standardized. Twenty-channel recordings of N100 and P300 were obtained for off-line analysis. P300 was elicited using an oddball paradigm with rare target tones interspersed among frequent non-target tones. Additionally, neuropsychological tests (syndrome short test SKT and letter cancellation test) were carried out. Neurological examination and all tests were compared preoperatively and one week postoperatively. A significant deterioration in cerebral function was documented by the SKT score (P = 0.04), an increase in P300 latency (P = 0.004) and an increase of mistake rate in counting the P300 target tone (P = 0.02). No differences between preoperative and postoperative testing were found for letter cancellation, P300 amplitude and any N100 parameter. No correlation was found between the preoperative/postoperative changes in SKT score and P300 latency. P300 was proved to be an objective neurophysiological parameter that allows for the quantification of cerebral function after CABG.