[Near-infrared spectroscopy during hypothermic selective cerebral perfusion--a clinical study of its value]

The purpose of this study is to assess the value of near-infrared spectroscopic oxymetry (NIRO) in monitoring cerebral oxygenation and metabolism during selective cerebral perfusion (SCP) for surgery of the aortic arch. The measurement protocol during SCP comprised oxyhemoglobin (HbO2), deoxyhemoglobin (Hb), and total hemoglobin levels in the brain. From March 1994 through March 1997, 14 patients underwent surgical treatment of the aortic arch anomalies with intraoperative monitoring with NIRO. The temporary circulatory arrest was accomplished at a rectal temperature of 22 degrees C and the hypothermic SCP was employed for the cerebral protection. SCP was initiated at a flow rate of 10 ml/kg/min so as to maintain HbO2 at the same level as immediately before the circulatory arrest (baseline). The longitudinal changes of HbO2 level during the process revealed four different patterns and were grouped accordingly. Three of the patients maintained HbO2 level above the baseline during SCP (Group A). HbO2 level reached to the baseline at initial flow rate but decreased gradually thereafter in 4 patients (Group B). Gradual increment of the perfusion flow rate failed to elevate HbO2 level to the baseline in the 5 patients (Group C1). In this group, HbO2 level started to elevate about 60 minutes after the initiation of SCP. HbO2 level of the remaining 2 patients was absolutely resistant to the increment of SCP flow rate and kept low values throughout SCP (Group C2). All the patients recovered uneventfully without any neurological abnormality. Our analyses for the longitudinal behavior of the HbO2 level confirmed the previously reported evidences that the values were affected not only by perfusion flow rate but also by hemodilution, blood transfusion, and perfusion pressure. Furthermore, our present study disclosed another evidence that HbO2 level was strongly affected by subclavian steal phenomenon. Although there were no differences in the clinical outcome among the groups, referring to the theories that HbO2 level is better not to be departed from baseline level, it could be concluded that HbO2 level monitoring in the setting of the determined hematocrit and hypothermia was effective for securing the adequate demand and supply balance of the cerebral oxygenation. Our conclusion may extend further that NIRO is a useful means in determining the optimal perfusion flow rate of SCP during surgery of the aortic arch.