Acute renal failure

Acute renal failure in infants, children and adults

Acute renal failure (ARF) occurs in many critically ill patients regardless of age. A combination of events often seen in critical care settings, including shock, sepsis, hypoxia, and the use of potentially nephrotoxic medications, combine to make ARF an ongoing and important management issue in critical care medicine. Since the events leading to the development of ARF differ in infants, children, adults, and the elderly, the pathophysiology, clinical features, and treatment modalities do indeed have remarkable similarities among the different age groups.

Urinary osmolal changes in renal dysfunction following open-heart operations

Forty consecutive patients who underwent open-heart procedures using a hyperosmolar perfusion prime were studied to determine the significance of free-water clearance and urinary osmolality early after bypass in predicting the likelihood of postoperative renal dysfunction, defined as a blood urea nitrogen (BUN) level over 50 mg/100 ml. Urinary osmolality increased in all patients during the first 18 hours after bypass, but the increase was substantially less for those who subsequently developed renal dysfunction. Free-water clearance, which was significantly less negative in the patients with renal dysfunction by 2 hours after bypass and remained so throughout the 18 hours of this study, served as an early postoperative indicator of impaired renal function in the patients who eventually developed BUN elevation. Moreover, it was more sensitive as an index of renal dysfunction than was osmolality alone. Early recognition of renal impairment is important, as it may prevent dangerous fluid overloading and allow for corrective measures to be undertaken before frank renal failure develops.

Cholangitis with acute renal failure: priorities in therapeutics

Obstructive cholangitis with acute renal failure is a dramatic syndrome which merits individual definition. Twenty-one patients with acute suppurative cholangitis complicated by rapidly developing renal insufficiency were studied, and the severity of the renal failure, an acute interstitial tubulopathy, bore no significant relationship to the serum bilirubin level. The mechanism of renal damage was clearly related to episodes of septicemia. Increasing experience has modified the approach to treatment. The dominant septic problem can often be controlled by vigorous antibiotic and fluid therapy, allowing time for spontaneous improvements in renal function. All patients thus operated at a distance from the septic episode survived. If emergency operation is required because of persistent or recrudescnet sepsis, the necessity for dialysis should be considered first; the circumstances demanding dialysis are defined. The priorities in therapy are then: 1) treatment of the infection, 2) treatment of the renal failure, and finally 3) operation. The amount of the operation depends on the evolution of the sepsis, but should be preceded by dialysis when required.

Renal blood flow in acute epidemic nephritis (nephropathia epidemica of Scandinavia)

Different haemodynamic and functional parameters were studied in 5 cases of acute epidemic nephritis with uraemia using nephroangiography and dye-dilution measurements combined with determination of extraction ratio and clearance for 51Cr-EDTA and PAH. In the acute phase, with greatly reduced renal function, increased vascular resistance was noted in spite of the vasodilatation observed in the renal artery out to and including the interlobular arteries. Moreover, angiography revealed enlarged kidneys with an increase in the thickness of the cortex and reduced cortical contrast accumulation. The renal blood flow, which was normal or slightly reduced initially, increased during convalescence, and renal function returned to normal. The investigation indicated that a primary vascular lesion in glomerular to postglomerular capillaries gives rise to pronounced interstitial oedema, which, probably as a result of secondary tubular compression, may be the cause of the rapidly developing renal failure.

Management of acute renal failure

Acute renal failure has oliguria and uraemia as its cardinal manifestations. The syndrome may be due to acute tubular necrosis, glomerulonephritis, urinary tract obstruction and occlusive vascular disease.

The renal damage due to acute tubular necrosis is of uncertain aetiology. Renal cortical ischaemia and depression of glomerular filtration rate are important in the pathogenesis. Activation of the renin-angiotensin system and glomerular coagulation may prove to be important in these changes.

The differentiation between reversible oliguria and established renal failure is generally accomplished on clinical grounds and the response to a therapeutic trial of mannitol. Measurement of urinary sodium concentration and osmolality are valuable adjuncts.

The keystone of management is the prevention of symptomatic uraemia. Infection and haemorrhage have now replaced pulmonary oedema and hyperkalaemia as the major causes of death. The mortality rate remains high in acute tubular necrosis and a significant mortality occurs in the diuretic phase.

Renal performance in patients undergoing replacement of the aortic valve

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.