Near-infrared spectroscopy as a possible device for continuous monitoring of arterial carbon dioxide tension during cardiac surgery

Background: Insufflation of carbon dioxide (CO2) to the operative field has been used to prevent major organ injury attributed to air embolisms in cardiac surgery. However, it may be preferable to avoid hypercapnia induced by CO2 insufflation, owing to its potentially harmful effect. To investigate the effectiveness of near-infrared spectroscopy (NIRS) as a possible method for continuous monitoring of arterial CO2 tension during cardiac surgery, we evaluated the correlation between the change in arterial CO2 tension and the change in regional cerebral oxygen saturation (rScO2) obtained from NIRS in as controlled a condition as possible. Methods: Thirty patients who underwent surgical correction for atrial or ventricular septal defects were enrolled in this study. Patients who had pulmonary hypertension or other intracardiac anomalies were excluded. Anesthetic and cardiopulmonary bypass (CPB) management were conducted according to our standard institutional practice. Data obtained from arterial blood gas analyses and corresponding regional cerebral oxygen saturation (rScO2) recorded from NIRS before and after the insufflations of CO2 during CPB were used for analysis. Results: The change in arterial CO2 tension correlated with the change in rScO2 in the left hemisphere (r = 0.681, p <0.001, y = -1.393 + 0.547x) and right hemisphere (r = 0.690, p <0.001, y = -1.999 + 0.486x). To control the effects of other variables, including hematocrit and temperature, these relationship were not reduced (left hemisphere: r=0.678, p<0.001; right hemisphere: r=0.634, p<0.001). Conclusions: Since the change in regional cerebral oxygen saturation was correlated with the change in arterial CO2 tension during mild hypothermic CPB, NIRS might be a possible non-invasive method for monitoring of arterial CO2 tension without incurring additional cost in this setting.