Associations among preoperative transthoracic echocardiography variables and cerebral near-infrared spectroscopy values at baseline before anesthesia in patients undergoing cardiac surgery: a retrospective observational study.

Cerebral tissue oximetry with near-infrared spectroscopy (NIRS) is used to monitor cerebral oxygenation during cardiac surgery. To date, reduced baseline cerebral NIRS values have been attributed to reduced cerebral blood flow primarily based on a significant positive correlation between left ventricular ejection fraction (LVEF) and baseline rSO2 measured with the INVOS 5100C oximeter. Reportedly, however, rSO2, but not StO2 measured with the FORESIGHT Elite oximeter, correlated with LVEF. We, thus, investigated associations among baseline NIRS values measured with three different oximeters before anesthesia for cardiac surgery and preoperative transthoracic echocardiography (TTE) variables, including LVEF, to examine whether there are inter-device differences in associations among baseline NIRS values and TTE variables. Using Spearman's correlation coefficient, we retrospectively investigated associations among 15 preoperative TTE variables, including LVEF, and baseline NIRS values, including rSO2, StO2, and TOI with the NIRO-200NX oximeter in 1346, 515, and 301 patients, respectively. Only rSO2 (p < 0.00001), but not TOI or StO2 (p > 0.05), positively correlated with LVEF. On the other hand, baseline rSO2, TOI, and StO2 consistently, negatively correlated with the left atrial diameter index (LADI), early diastolic transmitral flow velocity (E), E-to-early diastolic mitral annular velocity ratio (E/e'), estimated right ventricular systolic pressure (eRVP), and inferior vena cava diameter index (IVCDI) (p < 0.0005 to p < 0.00001). Because all of these five TTE variables could be positively associated with right as well as left ventricular filling pressure, our results indicated that reduced baseline NIRS values were consistently associated not with reduced LVEF but with TTE findings indicative of elevated biventricular filling pressure. Our data suggest that regional venous congestion greatly contributes to reduced baseline NIRS values in patients undergoing cardiac surgery.

Cerebral oxygen saturation (rSO2) during cardiopulmonary bypass (CPB) measured using the INVOS oximeter closely correlates with baseline rSO2.

Baseline cerebral regional saturation (rSO2) measured using the INVOS 5100C (Medtronic, MN, USA) varies widely among patients with cardiac and/or renal diseases. To identify significant correlates of baseline rSO2 and to investigate intraoperative rSO2 changes, we conducted a retrospective study in 494 patients undergoing on-pump cardiovascular surgery. Correlations between preoperative blood laboratory test variables and baseline rSO2 before anesthesia were examined. Intraoperative rSO2 changes were analyzed. Of all the variables examined, log-transformed B-type natriuretic peptide (BNP) most significantly and negatively correlated with baseline rSO2 (r = - 0.652, p < 0.0001). Intraoperatively, rSO2 showed the lowest value during cardiopulmonary bypass (CPB) (median rSO2: 56.2% during CPB vs. 63.9% at baseline, p < 0.0001). Although rSO2 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 rSO2 (r = - 0.589, p < 0.0001). Thus, patients showing low baseline rSO2 primarily associated with preoperatively high BNP continued to show low rSO2 even during CPB independent of hemodynamics artificially controlled by CPB. Our findings suggest that low baseline rSO2 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 rSO2 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.