ABNORMAL RENAL TUBULAR BACK-DIFFUSION FOLLOWING ANURIA

Renal distribution volumes of indocyanine green, ( 51 Cr)EDTA, and 24 Na in man during acute renal failure after shock. Implications for the pathogenesis of anuria

The mechanism responsible for the anuria in acute renal failure after shock is still controversial. Suppressed glomerular filtration and/or tubular back-diffusion of the filtrate are major possible causes. In the present investigation, seven patients with acute anuria, three of these seven again in the polyuric phase, six patients with moderate renal impairment, four patients with chronic renal failure, and eight subjects with normal renal function were studied by a multiple indicator-dilution method in which the total renal blood flow and renal distribution volumes of indocyanine green, [(51)Cr]EDTA, and (24)Na were determined. In normal subjects the average values for one kidney were 582 ml/min, 42 ml, 92 ml, and 139 ml, respectively. The measurements in the patients with moderate renal impairment were similar to those in the normal subjects, but were decreased in chronic renal failure. In acute anuria, the average values were 269 ml/min, 40 ml, 101 ml, and 114 ml and the kidney volume, estimated radiographically, was increased by 40%. When expressed as milliliters per milliliters kidney, the average distribution volume of (24)Na was decreased from 0.64 to 0.38. This decrease is consistent with the hypothesis that suppressed filtration is largely responsible for the anuria and that back-diffusion is, at most, a contributory factor. The apparent contradiction between the relatively well-preserved total blood flow and the suppressed filtration may be due to a combination of afferent vasoconstriction and efferent vasodilatation. This view is supported by the observation that low filtration fractions were found in clearance measurements performed during the polyuric phase.