Blood coagulability and hematological changes in calves with chronic centrifugal biventricular bypass pumps

A Hemadyne centrifugal pump was used to determine the effects of long-term circulatory assist on platelet number and aggregability. Five calves were supported on biventricular bypass with a pair of Hemadyne centrifugal pumps. On the 7th postoperative day (POD), the heart was fibrillated after pump flow rates were increased to compensate for the total cardiac output. The animals were anticoagulated with heparin throughout the study and adjustments were made to maintain the activated clotting time at between 180 and 220 sec. To maintain the activated clotting time level in the therapeutic range, it was necessary to gradually increase the heparin dose with time due to the developing heparin tolerance. Fibrinogen levels increased significantly on the 3rd postoperative day when compared to the preoperative control value. Platelet aggregation was measured using a whole blood impedance method with adenosine diphosphate and collagen as agonists. Platelet function was found to be significantly depressed following the biventricular bypass procedure (P < 0.05 on the 7th, 14th, and 21st POD). Platelet numbers were significantly decreased compared to the preoperative control values, being the lowest on the 1st and 3rd POD, recovering to 76% of the control values by the 7th POD, and then gradually decreasing to the 55% level by the 28th POD. These results show that, when tested for up to 4 weeks following surgery, both platelet number and function in calves supported with centrifugal pumps remain depressed. Despite the progressive heparin tolerance and suppressed platelet number and function, none of the animals showed abnormal bleeding tendencies on biventricular bypass.