Cerebral oxygen saturation (rSO) during cardiopulmonary bypass (CPB) measured using the INVOS oximeter closely correlates with baseline rSO.

Baseline cerebral regional saturation (rSO) measured using the INVOS 5100C (Medtronic, MN, USA) varies widely among patients with cardiac and/or renal diseases. To identify significant correlates of baseline rSO and to investigate intraoperative rSO changes, we conducted a retrospective study in 494 patients undergoing on-pump cardiovascular surgery. Correlations between preoperative blood laboratory test variables and baseline rSO before anesthesia were examined. Intraoperative rSO changes were analyzed. Of all the variables examined, log-transformed B-type natriuretic peptide (BNP) most significantly and negatively correlated with baseline rSO (r = - 0.652, p < 0.0001). Intraoperatively, rSO showed the lowest value during cardiopulmonary bypass (CPB) (median rSO: 56.2% during CPB vs. 63.9% at baseline, p < 0.0001). Although rSO during CPB correlated positively with hemoglobin concentration and oxygen delivery during CPB (r = 0.192, p < 0.0001; and r = 0.172, p = 0.0001, respectively), it correlated much more closely with baseline rSO (r = - 0.589, p < 0.0001). Thus, patients showing low baseline rSO primarily associated with preoperatively high BNP continued to show low rSO even during CPB independent of hemodynamics artificially controlled by CPB. Our findings suggest that low baseline rSO in patients with high BNP due to cardiac and/or renal diseases is more likely to result from tissue edema causing alterations in optical pathlength and thus in calculated rSO values, not readily modifiable with CPB, rather than actual cerebral hemodynamic alterations readily modifiable with CPB. These may partly explain why the INVOS oximeter is a trend monitor requiring baseline measures.