Moderate and extreme hemodilution in open-heart surgery: fluid balance and acid-base studies

Two groups of patients underwent aortic valve replacement. Fifteen patients received moderate hemodilution (mean hematocrit, 27%) with 40% donor blood in the priming solution. Extreme hemodilution was used in 14 patients (mean hematocrit, 18%) with a nonhemic prime and withdrawal of blood at the start of operation. Both groups were given more than 7 liters of fluid during operation; donor blood was primarily used in the moderately diluted patients, and Ringer's acetate was primarily given to the other group. The diuretic response to this fluid load was much more pronounced in the extreme than in the moderate hemodilution group. Eighteen hours postoperatively, patients in the moderate and extreme hemodilution groups had an excess of about 2 and 1.5 liters of water, respectively. In the patients who had moderate dilution an average of 1,000 ml of erythrocytes disappeared from circulation; no such disappearance could be found in the other group. The moderate group showed significantly lower arterial PO2 postoperatively than the extreme group. There were, however, no differences between the two groups in mixed venous PO2 during perfusion or in acid-base and osmolality values.