The proposed use of a 'screening test' to assess oxygenator performance

This study aimed to assess whether the use of the physiological shunt equation could (within the first five minutes of initiating CPB) serve as a 'screen' to differentiate normal and dysfunctional oxygenator performance. If dysfunction severe enough to require replacement was necessary, the normothermic patient could be weaned from CPB and replacement would be carried out under safe, controlled conditions. This technique would require postponing the induction of hypothermia (if used), aortic cross-clamping, and arresting the heart until after this screen was completed. This study demonstrates that a strong negative correlation exists between the degree of blood shunting and the membrane's 0 2 transfer performance (r = -0.874). This relation enables us to predict 0 2 transfer performance when only the shunt fraction is known. Of the 41 oxygenators used in this study, 40 demonstrated normal, or below-normal, shunt fractions. Oxygen transfer performance at or above predicted levels would be anticipated for these oxygenators. One of the 41 oxygenators had mildly elevated shunt fractions, which we predicted would be associated with mild 0 2 transfer dysfunction. Based on the performance screen worksheet we created, replacement was not necessary since the oxygenator maintained high levels of 0 2 transfer in reserve despite its marginal performance dysfunction. Assessment of oxygenator performance dysfunction in this earliest phase of CPB would greatly reduce the incidence of emergency oxygenator replacement secondary to actual or perceived oxygenator failure later in the course of the procedure.