MIXED VENOUS OXYGEN-SATURATION DURING CARDIOPULMONARY BYPASS POORLY PREDICTS REGIONAL VENOUS SATURATION

Mixed venous oxygen saturation is generally accepted as an indicator o f adequacy of systemic oxygen delivery; however, cardiopulmonary bypas s (CPB) may alter this relationship. Major postoperative complications potentially secondary to inadequate oxygen delivery during CPB indica te that mixed venous oxygen saturation may not detect regional venous desaturation during CPB. We therefore tested the hypothesis that mixed venous oxygen saturation and pH did not predict regional venous oxyge n saturations and pH during 2 h of bypass in a swine model. Six immatu re swine (27-34 kg) received standard normothermic CPB. Sagittal sinus and portal vein oxygen saturations and blood gases were measured at 3 0, 60, 90, and 120 min of bypass. Although the venous reservoir oxygen saturation remained unchanged during 2 h of bypass, sagittal sinus sa turation and pH decreased significantly (66% +/- 3.3% to 33% +/- 2.2% and 7.38 +/- 0.04 to 7.23 +/- 0.05, respectively). Likewise in the por tal vein, oxygen saturation and pH also decreased (82% +/- 2.4% to 59. 3% +/- 3.9% and 7.39 +/- 0.03 to 7.27 +/- 0.06, respectively). We conc lude that profound regional venous desaturation and progressive region al acidemia may go undetected even when a standard pump flow rate of 1 00 mL . kg(-1). min(-1) is used and mixed venous oxygen saturation is normal.