Cerebral and Somatic Near-Infrared Spectroscopy Measurements During Fluid Challenge in Cardiac Surgery Patients: A Descriptive Pilot Study

ObjectiveLittle is known about changes in near-infrared spectroscopy (NIRS)-derived cerebral (rSO2b) and somatic (rSO2s) oxygen saturation during a fluid challenge. The authors tested the hypothesis that they could differ from central venous oxygen saturation (ScvO2) and from one site to another.DesignA prospective observational study.SettingA teaching university hospital.ParticipantsFifty consecutive adult patients.InterventionsAdmission to the intensive care unit after cardiac surgery and investigation before and after a fluid challenge.Measurements and Main ResultsSimultaneous comparative ScvO2, rSO2b, and rSO2s data points were collected from a blood-gas analyzer and the EQUANOX monitor (Nonin Medical, Inc, Plymouth, MN). Correlations were determined by linear regression. Multiple stepwise linear regression models were used to assess independent variables associated with changes in ScvO2, rSO2b, and rSO2s. A statistically significant relationship was found between absolute values of ScvO2 and rSO2b (r = 0.42, p < 0.001) but not between absolute values of ScvO2 and rSO2s (r = 0.18, p = 0.066). No relationship was found between percent changes in ScvO2 and rSO2b (r = 0.05, p = 0.715) and between percent changes in ScvO2 and rSO2s (r = 0.02, p = 0.886) after the fluid challenge. Cardiac index contributed to the prediction of changes in ScvO2 (regression coefficient = −4.09, p = 0.006), whereas the mean arterial pressure contributed to the prediction of changes in rSO2b (regression coefficient = −0.05, p = 0.027).ConclusionsrSO2b and rSO2s cannot be used to provide noninvasive estimation of ScvO2, and trends in rSO2b and rSO2s cannot be considered as noninvasive surrogates for the trend in ScvO2 after cardiac surgery. Different independent variables contribute to the prediction of ScvO2, rSO2b, and rSO2s.