Solute-free versus electrolyte-free water clearance in the analysis of osmoregulation.
BACKGROUND
Although attention has recently focused on electrolyte-free water clearance (E-CH2O) as a replacement for solute-free water clearance (CH2O), especially from the viewpoint of plasma sodium regulation, a thorough comparison of the two has yet to be conducted.


METHODS
CH2O and E-CH2O were systematically compared in normal subjects in different diuretic stages, including furosemide-induced solute diuresis, and in patients with renal disease.


RESULTS
The normal renal ability to conserve free water based on E-CH2O was only 41% of that based on CH2O. E-CH2O remained positive until the urinary osmolality exceeded 500 mosm/kg H2O, markedly different from the 300 mosm/kg H2O for CH2O. The difference between E-CH2O and CH2O could ultimately be attributed to urea osmolar clearance, i.e., urea excretion rate/plasma osmolality, which accounted for about 40% of the osmolar clearance. CH2O underestimated the free water clearance by about 1 ml/min on average at all diuretic stages.


CONCLUSIONS
E-CH2O is a more correct parameter than CH2O with regard to the regulation of both plasma sodium and plasma osmolality. However, there is the opinion that the concept of E-CH2O is difficult to understand and that E-CH2O is still not a generally accepted parameter. It is expected that the results of the present study will lead to more general acceptance.
Shimizu
Kurakazu
K
Sumiyoshi Clinic Hospital, Mito, Fourth Department of Internal Medicine, Tokyo Women's Medical University, Tokyo, Japan. aquamoon@mui.bioglobe.ne.jp
Kurosawa
Takeshi
T
Sanjo
Teizo
T
Hoshino
Masanobu
M
Nonaka
Tatsuya
T
D000328:Adult; D000465:Algorithms; D065092:Antidiuretic Hormone Receptor Antagonists; D004231:Diuresis / Q000187:drug effects; D004573:Electrolytes / Q000097:blood / Q000737:chemistry* / Q000652:urine; D005921:Glomerulonephritis / Q000175:diagnosis / Q000378:metabolism; D006801:Humans; D008297:Male; D014867:Water / Q000737:chemistry*; D014882:Water-Electrolyte Balance / Q000502:physiology*
D065092:Antidiuretic Hormone Receptor Antagonists; D004573:Electrolytes; D014867:Water