Renal Performance in Patients Undergoing Replacement of the Aortic Valve

Abstract

Renal performance of seven patients undergoing replacement of the aortic valve was investigated. The initial portion of cardiopulmonary bypass was characterized by low arterial blood pressure and anuria. With a subsequent rise in arterial pressure during bypass, urine flow suddenly increased in five patients. In two patients urine flow did not resume until immediately after cardiopulmonary bypass. The high rate of urine flow at these times is thought to be partially due to a glucose-induced osmotic diuresis. The glomerular filtration rate (inulin clearance) and the effective renal plasma flow (PAH clearance) fell with induction of anesthesia and opening of the chest, but there was no further drop in these functions as a result of total body perfusion. Urine osmolality fell significantly during and immediately after cardiopulmonary bypass. The changes in urine osmolality are thought to be due in part to the osmotic diuresis and in part to a temporary reduction in the renal medullary hyperosmolality secondary to hemodynamic changes. All of the alterations in renal function were reversible in the patients studied.

Anemia increases the risk of renal cortical and medullary hypoxia during cardiopulmonary bypass

“…These data relate to the findings that CPB is associated with a large fall in the urine osmolality, 26 suggesting that renal medullary dysfunction may result from an insufficient supply of O 2 required for active reabsorption in the renal medullary interstitium. The renal cortex also experienced tissue hypoxia at a delayed time during anemia-CPB, but with unchanged blood flow, which reinforces the idea that the deeper area of the kidney is more susceptible to hypoxic damage during anemia.…”

The effects of hypotension on renal function

“…Hg is frequently quoted as the minimum pressure necessary for glomerular ultrafiltration to occur (Corcoran and Page, 1943;Smith, 1951). I n a reportofa study on a similar group of patients to this present series, Mielke, Maher, Hunt, and Kirklin (1965) stated that urine secretion during full cardiopulmonary by-pass did not occur at arterial perfusion pressures below 60mm. Hg in their cases.…”

Acute Alterations of Body Composition after Open Intracardiac Operations

“…This same conclusion was reached in a previous study, in which patients undergoing aortic valve replacement were found to excrete an average of 12 mEq/24 hr in the first 3 days after operation in contrast to 55 mEq/24 hr preoperatively. 23 The data from this investigation indicate that exchangeable potassium is less 3 or 4 days after cardiopulmonary bypass than it was preoperatively. A recent study by Clark and colleagues,24 in which whole body potassium was measured by use of a total body counter, showed a decrease in whole body potassium of about 200 mEq between the preoperative study and that 48 hr later, a value similar to that in the present study.…”