Renal Excretion at Low Urine Volumes and the Mechanism of Oliguria

Abstract

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. MATERIAL AND METHODSSeries of excretion studies were carried out, using four normal non-pregnant adults, one normal pregnant woman at term, six patients with preeclamptic toxemia, one patient with terminal malignant nephrosclerosis and cardiac decompensation, one with Bright's disease, and one unclassified cardiac patient. In the normals, a thirty to sixty hour food and water fast was necessary to get the urine volume down to the desired level. In the toxemia patients, a twelve hour fast sufficed, while the patient with renal disease required no preparation. Most of the urines were taken at hourly intervals, though some were for longer periods up to three hours. When the completeness of collection was controlled by washing out the bladder, specimens were taken at intervals of twenty to thirty minutes. In the first two normals, voided specimens were used; in all other cases the urines were obtained by catheter. In the later experiments the urine was first collected, and then the bladder washed out twice with saline at the end of each collection. The washings were separately analyzed. The observed urine volume was corrected by adding the volume of urine calculated, from the creatinine, to be in the saline washings.The apparent plasma creatinine was determined in a modified Folin-Wu filtrate of the plasma, by the method of Folin and Wu (3). Urinary creatinine was determined by Folin's (3) method.For the determination of urinary nitrogen, 1 ml. of urine was diluted to volume in a 200 ml. volumetric flask. From this were taken 2, 3, and 5 ml. samples which were digested by the Wong persulphate method (4). After cooling, they were nesslerized and read against a standard containing 0.15 or 025 mgm. of nitrogen. Correction was made for protein whenever present.Inorganic phosphorus was determined in 1, 2, and 5 ml. samples of the urine diluted 1:200. Youngburg's method (3) was used.Total solids were determined indirectly, because of the small amounts of urine available. Using calibrated pipettes, 10, or when necessary, 5 ml. of urine were weighed to a tenth of a milligram. The specific gravity was then calculated and corrected for protein (for each 10 grams of protein per liter 0.0030 was subtracted from the specific gravity). The significant figures in the specific gravity were then multiplied by Long's coefficient, 2.6, to get the approximate total solid content (3).All data were fitted to...

Serum Creatinine and Renal Function

“…In normal dogs and humans, reabsorption has been observed when urine flow rate is very low (less than 0.5 ml per minute), perhaps as a result of passive diffusion of creatinine through the normal tubular and urinary tract epithelium (41)(42)(43). Dis orders in which creatinine reabsorption has been demonstrated include severe congestive heart failure and uncontrolled diabetes mellitus (44)(45)(46)(47)(48).…”

Effect of an Acute Oral Protein Load on Microalbuminuria in Uninephrectomized Patients in Relation to the Time Since Nephrectomy

“…In deed. reabsorption of creatinine has been reported in asso ciation with low urine flow rates in patients with uncontrol lable diabetes mellitus [481. in patients with congestive heart failure [49], and in normal subjects [50].…”

The Association Between Urine Output, Creatinine Elevation, and Death

“…Although we found that AKI-Cr developed in 38% (after 1 hour)-59% (after 12 hours) of patients with a UO below 0.3 mL $ kg -1 $ h -1 (21 mL/h for a 70-kg person)-AKI-Cr did not develop in 41 (62%). This suggests that AKI may have developed (we just did not measure Cr at the right time), but that UO and filtration increased sufficiently enough by the time of the next Cr measurement so that Cr had recovered to below that required for AKI-Cr or that these patient are able to concentrate their urine to a greater extent as found by Chelsey in his 14 patients [18]. Further study is needed to clarify this point.…”

“…The association between AKI and death (the third question) was determined using binary logistic regression, adjusted for age, height, type of operation, ejection fraction, baseline creatinine, and comorbidities with 95% confidence intervals (CIs) that excluded 1 and a p of less than 0.05 denoting statistical significance. No adjustment was made for multiple outcomes [18]. All statistics were done with R software (R Foundation, Vienna, Austria).…”

“…An early study showed that the glomerular filtration rate is preserved in fasted, dehydrated individuals until the UO falls to approximately 0.35 to 0.5 mL/min (21 to 30 mL/h) [18]. Below this value, the glomerular filtration rate falls linearly until anuria and no filtration are reached.…”