While evaluating the potential advantages of gravity drainage of the cavae, as compared with those of a venous pump, we found that verbal recommendations regarding the desirable distance between the right atrium and the blood level in the venous reservoir varied from 5 to 80 cm. H2 O. In plotting the relation of the caval drainage pressure gradient to the venous pressure in animals, we found that the curves had the same slope with varying flow rates and catheter sizes, and that they finally leveled off when the drainage gradient was less than 10 cm. H2O. Since all of the curves were parallel, it seemed apparent that the slopes were dependent upon the out flow pressure and resistance characteristics, primarily, since the size and length of the connecting tubing remained constant. When the caval catheters were nearly as large as the dog's cavae, the venous pressure could
KIRBY CK, GIANELLI S, McMICHAEL H, SCHUDER JC, McCAUGHAN JS, JOHNSON J. Simple Automatic Method of Blood Volume Control During Cardiac Bypass for Open Heart Surgery. AMA Arch Surg. 1959;78(2):193–196. doi:10.1001/archsurg.1959.04320020015003
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