MEASUREMENT OF EXTRACELLULAR FLUID BY MEANS OF A CONSTANT INFUSION TECHNIQUE WITHOUT COLLECTION OF URINE

Abstract

The volume of distribution of a substance may be detd. regardless of the route of removal of the substance from the body (a) if it is freely and rapidly diffusible, and (b) if it is removed from the body water compartment in which it is dissolved at a rate proportional to its concn. A constant infusion was used to determine the overall or total plasma clearance of mannitol, p-aminohippurate, thiosulfate and T1824, following which the infusion was stopped, and the decrement with time of plasma concn. was observed. The volume of distribution of each of these substances was calculated as the total plasma clearance divided by the post-infusion decrement with time (slope) of the natural logarithm of plasma concn., thus correcting for any metabolic or other extrarenal disposal. The mannitol space averaged 19.2% of body wt. in the dog and 17.3% of body wt. in man. The thiosulfate space averaged 17% of body wt. in the dog and 2 measurements of the thiosulfate space in man were 15.7 and 19.5% of body wt. The p-aminohippurate spaces were 27.5 and 26.6% of body wt. in 2 dogs and 28.5 and 26.2% of body wt. in 2 men. Measurements of the T1824 space in a human subject and in a dog were 5.94 and 7.9% of body wt., respectively.