Renal function in respiratory failure.

Respiratory failure produces significant changes in many aspects of renal function. Whereas in response to acute hypercapnia, body buffering mecha­ nisms are of primary importance in maintaining pH, in adaptation to chronic hypercapnia, increased renal excretion of acid is predominant. Augmented secretion of ammonia accounts solely for the net increase in renal acid excre­ tion. During chronic hypercapnia, increased reabsorption of bicarbonate by the kidney serves to maintain elevated extra-cellular bicarbonate concentra­ tion. In patients with chronic pulmonary disease, renal blood flow is usually re­ duced while glomerular filtration is less affected. Water and sodium excretion by the kidney is impaired when congestive failure is present. After recovery from heart failure, these parameters return towards normal levels. Renal blood flow and sodium excretion increase during moderate hypoxia but decrease significantly in response to severe hypoxia, hypercapnia, or to hyperoxia. Prolonged mechanical ventilation is often associated with renal water reten­ tion and congestive heart failure. Respiratory failure is associated with pro­ found alterations in the composition of body fluids. With ventilatory insufficiency, retention of carbon dioxide (hypercapnia), inadequate oxygenation (hypoxia) and res* Supported in part by a grant from the Otho S. A. Sprague Foundation, Grant T01-AM-05 from the National Institutes of Health, and Grant RR-48 from the National Institutes of Health, Division of Research Resources, to the Clinical Research Center of Northwestern University Medi­ cal School, Chicago, IL. fAddress requests for reprints to Norman M. Simon, M.D., Northwestern Memorial Hospital, Passavant Pavilion, 303 East Superior Street, Chicago, IL 60611. piratory acidosis ensue. These metabolic perturbations evoke multiple changes in renal function. As a compensatory mecha­ nism, renal acid excretion increases in re­ sponse to respiratory acidosis. In a less clearly adaptive reaction, renal hemo­ dynamics and water and sodium excretion decrease from normal levels. The purpose of this account is to review alterations of renal function in acute and chronic res­ piratory failure, and to discuss the effects of several therapeutic measures, emphasizing primarily data gathered from studies per­ formed in man.