By definition, perfusion is the process of nutritive delivery of arterial blood to a capillary bed in the biological tissue. The Perfusion Index, summarized in this slide, is a measurement displayed on many pulse oximeters and is beneficial in gauging the severity of illness in newborns. A low perfusion signal is more difficult to detect in the presence of motion artifacts, which are ideally removed from a pulse oximetry signal in order to obtain a more accurate SpO2 level. Patient motion and venous pulse motion add to this “noise” versus perfusion challenge and can mask the true SpO2 measurement.