Natriuresis during and early after cardiopulmonary bypass: relationship to atrial natriuretic factor, aldosterone, and antidiuretic hormone.

Because neurohumoral responses to cardiopulmonary bypass (CPB) are similar to those seen in shock, CPB might be expected to decrease renal blood flow; yet diuresis is commonly observed during and early after routine cardiac procedures with CPB. To examine this apparent paradox, we studied 15 patients before, during, and after CPB for coronary artery bypass grafting. Plasma levels of atrial natriuretic factor (alpha-ANF), aldosterone, and antidiuretic hormone (ADH) and urinary sodium excretion were measured before anesthesia, after sternotomy but before CPB, at 15 and 30 minutes of CPB, and at 15 and 30 minutes after discontinuation of CPB. alpha-ANF increased only slightly during CPB, and the initial natriuresis during CPB occurred in the presence of a markedly increased ADH level. After CPB ended, urine flow and sodium excretion increased in conjunction with increased alpha-ANF and normal ADH. We conclude that the early natriuresis during CPB occurs in the presence of a high ADH concentration, with no significant increase in plasma alpha-ANF. This may be a paradoxic response to supraphysiologic levels of ADH. The natriuresis after CPB appears to be strongly associated with increased alpha-ANF, present for at least the first 30 minutes after CPB, which could reflect alpha-ANF release resulting from atrial distention during volume loading.