A comparison of the NeurOs® and the INVOS 5100C® cerebral oximeter during variations of the partial pressure of carbon dioxide and fractional inspiratory concentration of oxygen

This prospective method comparison study compared cerebral oxygen saturation (ScO 2 ) measurement performance of the new cerebral oximeter (NeurOs®, Mespere LifeSciences, Ontario, Canada) in comparison to the established INVOS 5100C® (Medtronic, Boulder, USA) cerebral oximeter. We performed measurements during different levels of carbon dioxide pressure (PaCO 2 ) during hyper- and hypoventilation and different levels of arterial oxygen saturation (SaO 2 ) induced by variation of the inspiratory fraction of oxygen (FiO 2 ). 59 anesthetized cardiac and vascular surgical patients were studied during hemodynamically stable conditions. Two versions of the NeurOs® oximeter were used in 39 and 20 patients, respectively: an older version with one bi-hemispherical sensor attached to the midline of the forehead and a newer version with two sensors that were attached to the left and right forehead. Alternating measurements of ScO 2 with the INVOS® oximeter (bifrontal sensors) and the NeurOs® oximeter were performed during baseline conditions and after PaCO 2 had been randomly in- and decreased by changes in ventilation (constant FiO 2 ) and SaO 2 had been randomly modified by variations in FiO 2 (constant PaCO 2 ). Employing the most recent NeurOs® version, measurements were additionally performed in a default and a high penetration mode. Bland–Altman analyses revealed comparable bias and limits of agreement for INVOS® and NeurOS® measurements during baseline conditions when using the bi-hemispherical sensor and the version with two sensors, respectively. Consequently, further analyses were performed on the pooled data of 59 patients. Bland–Altman analysis for repeated measurements revealed a bias of − 0.5%, a lower limit of agreement of − 16.3% (95% CI − 19.6 to − 13.7%) and an upper limit of agreement of 15.4% (95% CI 12.8 to 18.8%) during variations of PaCO 2 . The respective analysis during changes in SaO 2 induced by variation of the FiO 2 revealed a bias of − 0.8%, a lower limit of agreement of − 16.3% (95% CI − 19.7 to − 13.6%) and an upper limit of agreement of 14.7% (95% CI 12.1 to 18.2%). Both analyses showed a proportional error. No significant differences in ScO 2 were observed during measurements with the bi-frontal sensors in the default as well as the high penetration mode. The ScO 2 measurement performance of the NeurOs® cerebral oximeter is not interchangeable with the INVOS® cerebral oximeter during variations of ventilation and oxygenation in elective cardiac or vascular surgical patients. The lack of reactivity to changes in ventilation (by variation of PaCO 2 ) and oxygen delivery (by variation of FiO 2 ) question the reliability of NeurOs® measurements to reflect changes in cerebral blood flow and cerebral oxygen balance. This holds true not only for different sensor positions at the forehead but also for different modes of penetration.