How near-infrared spectroscopy differentiates between lower body ischemia due to arterial occlusion versus venous outflow obstruction.

Small infants undergoing cardiac surgery are at high risk for regional malperfusion during cardiopulmonary bypass. We report a 13-day-old neonate who underwent reconstruction of the aortic arch and closure of atrial and ventricular septum defects. Near-infrared spectroscopy probes were placed on the forehead and the calf to monitor tissue oxygenation and hemoglobin concentrations. During rewarming, after deep hypothermic circulatory arrest, the patient's calf hemoglobin concentration immediately increased but oxygenation remained low. Repositioning of the venous cannula resolved this suspected venous congestion. Simultaneous monitoring of tissue oxygenation and hemoglobin concentration allows differentiation of arterial obstruction from venous congestion.