Detection of cerebral desaturation during cardiopulmonary bypass by cerebral oximetry

As oxygen consumption increases acutely during rewarming period in extracorporeal cardiopulmonary bypass (CPB), it is crucial to maintain cerebral oxygen delivery at this critical moment. The aim of this study was to evaluate the effectiveness of a cerebral oximeter (INVOS 3100, Somanetics Corporation, Troy, MI, USA) in monitoring cerebral oxygen balance during rewarming in CPB by correlating optical spectroscopic determinations with jugular bulb oxyhemoglobin saturation measurements.

On trial were 15 patients who underwent cardiac surgery under moderate hypothermic nonpulsatile CPB. Infrared spectroscopic soma sensor was placed over the patient's left frontal area to continuously monitor the regional cerebral oxygen saturation (SrO2) and the ipsilateral internal jugular vein was cannulated for measurement of venous oxyhemoglobin saturation (SjO2) at the jugular bulb. The changes of SjO2, SrO2, mean arterial pressure (MAP) and nasopharyngeal temperature (NPT) were recorded 5 min before CPB, instantaneously at initiation of CPB and at the point where every increment of 1 degree C in NPT was reached during CPB rewarming. The data obtained were statistically analyzed for any correlation between two methods using repeated measurements of ANOVA and linear regression.

There was no correlation between SjO2 and SrO2, between MAP change and SjO2 or SrO2 at the start of CPB, but a significant reduction of SjO2 during rewarming period was observed which was inversely correlative with NPT changes (r(2) = 0.64, p < 0.05). However, SrO2 did not show a similarity.

Jugular bulb desaturation which correlated inversely with rewarming speed as disclosed in this study indicated that the temperature change during rewarming was crucial for cerebral oxygen balance. Being less sensitive and still more unspecific, the INVOS 3100 cerebral oximeter is incapable and not recommended for monitoring cerebral oxygen saturation in CPB.