Pathophysiology and management of renal insufficiency in the perioperative and critically ill patient.

Acute renal failure (ARF) is defined as azotemia and decreased urine output secondary to a sustained decline in the glomerular filtration rate (GFR). In the postoperative and ICU settings, however, the classic markers of renal insufficiency can be misleading. The blood urea nitrogen (BUN) level can be increased in the face of gastrointestinal bleeding, catabolic states, and medications like steroids; and the creatinine level can be influenced by muscle mass and acute muscle injury. An abrupt change in the urine output frequently heralds ensuing renal failure. In the literature, the incidence of ARF in the postoperative period and in the ICU setting ranges from 7% 26 to 15%. 60 Exact estimates, however, are difficult to ascertain, given the variable definitions of ARF. These estimates likely will prove to be conservative in the face of an aging population and the increased number of patients being supported through multisystem organ dysfunction. For example, a study that attempted to elucidate the natural history of patients diagnosed with culture-positive septic shock found the incidence of ARF to be 51%. 73 Whether ARF itself is an independent predictor of a poor outcome or merely another component of multisystem organ dysfunction remains controversial. Acute renal failure associated with increased mortality has been well documented in the cardiac 1,5,30,100 and vascular surgery 47,94 literature. The most recent study by Chertow et al 30 revealed a 63.7% mortality rate for patients requiring dialysis following cardiac surgery versus 4.3% for patients with intact renal function, even after adjusting for comorbidities and postoperative complications. Even when more conservative definitions of ARF are used, the mortality remains excessive. A recent study of medical patients requiring bone marrow transplantation revealed an 87% versus 37% versus 17% mortality for patients requiring dialysis, for those who doubled their creatinine and for patients with normal renal function, respectively. 98 Another study that used a more conservative definition of renal insufficiency that did not include dialysis also revealed a mortality rate of 67%, as compared with 19.4% in patients with intact renal function. 60 Studies examining all admissions to the ICU revealed similarly poor outcomes, but most of these cases occurred in the presence of multisystem organ dysfunction. 26,29,55,65 Despite advances in ICU supportive care and renal replacement therapy, the mortality from ARF in the critically ill patient remains high. Efforts directed at prevention of renal insufficiency are important, given the lack of specific treatments of proved benefit. This article discusses the causes of ARF that are most common in the postoperative and critically ill patient, with some suggestions for diagnosis, prevention, and management. Emphasis is placed on the pathophysiologic mechanisms involved in the progressive development of acute renal insufficiency in this patient population rather than on the presence of more chronic forms of renal failure, including glomerulonephritis, acute interstitial nephritis (AIN), and nephrotic syndrome.