Abstract
Mixed venous oxygen tension was as well rerated to cardiac index as to arterial oxygen tension after open cardiac surgery. In an anesthetized dog, relationship between mixed venous Po2 and arterial Po2 at different levels of cardiac output with right chest open, or of artificial pump output under pulsatile total cardiopulmonary bypass with a closed perfusion system containing membrane oxygenator, was evaluated. Continuous monitoring of respiratory and blood gas tension with two mass spectrometers demonstrated that, when arterial oxygen tension was increased gradually, the higher was the level of mixed venous Po2 and the more pronounced was its rise, as cardiac output or artificial pump output was maintained at the higher levels. Calculated venous admixtures were lowest when inspired oxygen fractions were between 0.35 and 0.6.
