critical care medicine
Oliguria
Key Points
Categories of causes of oliguria include decreased renal blood flow, renal insufficiency, and urinary outflow obstruction. History and physical examination often suggest a mechanism (eg, recent hypotension, nephrotoxic drug use). Measure serum electrolytes, bloodureanitrogen, and creatinine. Measure urine sodium and creatinine concentration, and calculate fractional sodium excretion if it is unclear whether the cause is prerenal or renal; a ratio<1 indicates the problem is prerenal, a ratio>2 indicates acute tubular necrosis, and ratios between 1% and 2% are indeterminate. For patients taking diuretics, measure urine and plasmaureaas well as urine and plasma creatinine and calculate the fractional excretion ofureato determine if the cause is prerenal or renal;<35% indicates the problem is prerenal;>50% indicates the problem is acute tubular necrosis; and 35% to 50% indicates the etiology is indeterminate 