Effect of anesthesia and surgery on renal function.

Interpretation of the effects of anesthesia and surgery on renal function should be based on careful appraisal of the methodology used. Currently, the most accurate measurement of in vivo RBF is provided by flow probes, although thermodilution techniques show promise. In addition, the many secondary factors that affect renal responses, such as intravascular volume status and positive pressure ventilation, should be taken into consideration in evaluating any study. Normal renal function appears to be regulated by a balance between opposing neurohormonal systems which control vasomotor tone, diuresis, and natriuresis. Surgical stress tips the balance in favor of renal vasoconstriction and salt and water retention, which may last for days after operation. Recent elucidation of the role of atrial natriuretic peptide enhances the concept that these changes can be prevented or modified by maintenance of normal or increased atrial volume. Anesthetic agents generally decrease GFR and urine output. Effects of RBF are variable and probably reflect overall circulatory responses rather than direct actions. All these changes are mild and usually reversed at the end of anesthesia. Positive pressure ventilation depresses renal function through its effects on the central circulation, which can be reversed by administration of fluid or inotropic agents. Controlled hypotensive anesthesia, aortic cross-clamping, and cardiopulmonary bypass represent anticipated renal insults which should be carefully managed.