[Clinical study on measurement of cerebral metabolism and oxygenation during cardio-pulmonary bypass by near-infrared spectrophotometry].

We studied the non-invasive method of monitoring of cerebral metabolism and oxygenation of patients mainly with thoracic aortic aneurysm during Cardio-pulmonary bypass (CPB) by Near-infrared Spectrophotometry (NIRS) to establish the safety limits of cerebral perfusion. NIRS monitoring of all 12 patients showed that cerebral oxygenation levels were maintained within the pre-CPB range when mean arterial perfusion pressure (MAPP) was above 60 mmHg. With considering rectal temperature, the cerebral oxygenation levels were maintained above the pre-perfusion baseline when MAPP was above 50 mmHg at rectal temp. < or = 25 degrees C, and 73 mmHg at > or = 25 degrees C. It was suspected that cerebral autoregulatory mechanism could exist even in hypothermia (< or = 25 degrees C) because cerebral oxy-Hb and blood volume was significantly declined when MAPP was reduced to 40 mmHg or less. In 5 patients who underwent selective cerebral perfusion, the base line level of blood volume was preserved when the perfusion flow rates were above 0.5l/min, and the desirable oxy-Hb levels were obtained when the flow rates were above 0.4l/min. During deep hypothermic circulatory arrest (18 degrees C), cerebral oxy-Hb level was gradually reduced from baseline, reflecting proceeding metabolic activity even in profound hypothermia. These findings led us to conclude that non-invasive, continuous, and direct monitoring of cerebral oxygenation using NIRS can provide valuable data to prevent cerebral injury after CPB. It is hoped that the safety limits of cerebral perfusion and circulatory arrest can be established in the future using multiple analysis of pressure, flow, temperature, Hb concentration and so far by NIRS.