The effects of systemic oxygenation on cerebral oxygen saturation and its relationship to mixed venous oxygen saturation: A prospective observational study comparison of the INVOS and ForeSight Elite cerebral oximeters

Purpose The present study aimed to test the hypothesis that cerebral oxygen saturation (ScO 2 ) measurements with the INVOS-5100-C and the ForeSight-Elite cerebral oximeters vary in their correlation with mixed venous oxygen saturation (SvO 2 ) upon changes in systemic oxygenation in extubated cardiac surgical patients. Additionally, we aimed to elucidate whether the ScO 2 measurements of both devices can be used interchangeably to detect reduced SvO 2 . Methods Forty-eight spontaneously breathing patients extubated after cardiac surgery were included in this prospective observational study. The patients were exposed to both high (10 oxygen L·min −1 via face mask) and low (room air) inspiratory oxygen concentrations. Bi-hemispherical ScO 2 was determined with the INVOS and ForeSight Elite cerebral oximeters. The SvO 2 was measured with a pulmonary artery catheter. Results Significant changes in oxygen delivery, ScO 2 (by both cerebral oximeters), and SvO 2 were observed upon variation of oxygenation. The minimum mean (standard deviation) ScO 2 (ScO 2min ) using the INVOS and ForeSight did not differ significantly during high oxygen delivery [63.1 (8.6) % vs 65.8 (4.7) %, respectively; P = 0.07], but during low oxygen delivery, the INVOS value was significantly lower than that of the ForeSight oximeter [56.7 (8.9) % vs 61.3 (4.4) %, respectively; P = 0.003]. Both devices differed in the correlation between ScO 2min and SvO 2 for the combined oxygenation data (0.59, INVOS vs 0.28, ForeSight; correlation difference, 0.31; Bonferroni-adjusted 95% confidence interval [CI], 0.08 to 0.54; P = 0.008). The receiver-operating curve analysis revealed an area under the curve of 0.83 (95% CI, 0.74 to 0.9; P = 0.005) for detecting an SvO 2 below 50% by ScO 2min with the INVOS and 0.51 (95% CI, 0.41 to 0.62; P = 0.92), respectively, with the ForeSight. Conclusions These findings suggest that the cerebral oximeters tested react differently to variations in systemic oxygenation and in their relationship with SvO 2 and thus give different information on cardiopulmonary function. These findings raise doubt about whether these devices should be used interchangeably.