Extending the limits of hemodilution on cardiopulmonary bypass using stroma-free hemoglobin solution

Ten swine were subjected to exchange transfusion to a hematocrit level of 5% with either stroma-free hemoglobin solution (SFHS) or 7% albumin solution. Myocardial performance, oxygen kinetics, and myocardial metabolism were subsequently examined using a perfused, in situ, right heart bypass, swine heart model with control of preload, afterload, and heart rate. Animals were tested during a control period (hematocrit = 30%) and following exchange transfusion with either solution to a hematocrit level of 5%. We found that myocardial performance following albumin solution exchange could not be sustained on right heart bypass, and these animals had a stroke volume of zero at a left ventricular end-diastolic pressure of 14 torr. SFHS animals had a significant drop in stroke volume at 14 torr following exchange (20 +/- 3 versus 10 +/- 4, p < 0.025), but this 50% performance level could be sustained. Coronary blood flow rose and myocardial oxygen consumption fell in both groups, although the statistically nonsignificant mean differences were less with SFHS. Arterial-coronary sinus oxygen difference fell significantly (p < 0.05) with albumin solution (7.3 +/- 0.8 versus 2.2 +/- 0.2) and nonsignificantly with SFHS (5.6 +/- 0.4 versus 4.1 +/- 0.7). Lactate production occurred in both groups, but was greater with albumin (34% +/- 6%) than with SFHS (3% +/- 16%). No changes in myocardial tissue gasses were noted in either group. Although myocardial performance decreased and some lactate production occurred with SFHS, we believe these comparative results provide promise in the eventual utilization of an oxygen-carrying agent such as SFHS to extend the limits of hemodilution to a hematocrit value of 5% or less.