ON THE AVAILABILITY OF OXYGEN TO THE BODY DURING CARDIOPULMONARY BYPASS IN MAN

The adequacy of tissue perfusion during cardiopulmonary bypass, with and without moderate hypothermia, was assessed in 33 adult patients undergoing open-heart sur-gery. The criterion of adequacy chosen was the whole-body oxygen consumption, suitably adjusted for weight and temperature. Within the range of pump-flows generally used, a low mixed-venous oxygen tension and a high arteriovenous oxygen-content difference were associated with better tissue oxygenation than their converse. It is argued that arteriovenous shunting is an important determinant of tissue oxygenation during cardiopulmonary bypass. Blood concentrations of pyruvate and lactate were not significantly correlated with the availability of oxygen to the tissues. The use of mixed-venous oxygen saturation (Sv02) as an indication of the adequacy of cardiopulmonary bypass (CPBP) during cardiac operations, and of cardiac output during the immediate post-operative period, was suggested many years ago (Clark, 1958; Boyd et al., 1959; McArthur et al., 1962). Mor