Postdialytic Changes in Serum Osmolarity and in Blood Urea of 23 Patients

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PATIENTS in chronic renal failure, and to a lesser extent those in acute renal failure, may have a relative decrease in urinary output after treatment with the artificial kidney. It has been suggested that the cause of this postdialytic “oliguria” may be due to a decrease in osmotic load. We know of no study that substantiates or refutes this thesis, and therefore undertook to investigate a possible correlation between postdialytic changes in urinary output and in osmolarity of serum.

Methods and Material

Twenty-three patients in different stages of acute and chronic renal failure were treated with twin-coil disposable artificial kidneys for a total of 64 dialyses. Before and after each dialysis, samples of blood were taken for standard laboratory tests and to determine the osmolarity of the serum. For control purposes, 24 samples of blood were taken from normal blood donors for determinations of osmolarity of the serum. Determinations of concentrations of sodium, chloride, bicarbonate, and urea in the serum, and of hematocrit readings were performed in our hospital laboratory under the supervision of John W. King, M.D., Ph.D., and Willard R. Faulkner, Ph.D.

Osmolarity of serum was determined with the Fiske osmometer, which operates on the physical principle that both the osmotic pressure of a solution and the depression of the freezing point of the solvent are directly proportional to the molecular concentration of the dissolved substance (the total ion and molecular counts in the case of ionized solutions). The osmometer measures the depression of the freezing point, but. . .



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