Renal Excretion at Low Urine Volumes and the Mechanism of Oliguria.

In previous papers (1, 2) it was shown that when the urine volume output falls below about 0.35 ml. per minute, the urine becomes " maximally" concentrated with respect to urea. The urea concentration of the urine is constant below this critical volume, and thus the urea clearance (U V/B) varies directly and quantitatively with the urine volume (V). In an effort to analyze the mechanism of renal excretion at low urine volumes, the plasma clearance of endogenous creatinine, and the excretions of phosphorus, total nitrogen, and total solids have been studied in a series of oliguric subjects. These findings are the basis for this report.