INULIN SPACE AS A MEASURE OF EXTRACELLULAR FLUID

Abstract

A new method was devised which permits the use of inulin as a measure of the extracellular space, by means of an equilibrating infusion followed by the collection of the total inulin excreted after the cessation of the infusion. The length of infusion necessary to insure uniform distribution of inulin throughout the extracellular space is 2 hrs. in the dog. A method is described to measure the delay time which permits the correction of the total urinary inulin recovery. This delay time is inversely proportional to the rate of urine flow so that the product of these 2 quantities offers an approximation of the renal dead space (6 cc. in the dog). This infusion method measures the same space in the normal dog that the single injn. method measures in the nephrectomized dog. The avg. extracellular space of the dog is 19.4% of body wt. compared to 30.4% and 33. 8% for the spaces of distribution of Na24 and thiocyanate, respectively.