Body fluid composition in chronic renal failure.

Studies were performed to assess body fluid composition alterations occurring in 10 patients undergoing chronic hemodialysis. Red cell mass (RCM), plasma volume (PV), extracellular fluid volume (ECF), and total body water (TBW) were assessed 24 hours following hemodialysis to dry weight, following infusion of normal saline to increase body weight by approximately 2 kg, and following hemodialysis to decrease body weight by approximately 2 kg. Results demonstrate that TBW constituted from 48.5 to 51.0% of body weight. The ECF constituted from 41.8 to 46.3% of the total body water. The ratio of PV to interstitial fluid (ISF) volume (ISF = ECF - PV) approximated 1.1 to 1.2:3. Salt and water alterations (isotonic saline infusion and ultrafiltration) were restricted to the ECF component of the TBW. In the ECF, it was principally the ISF that buffered salt and water expansion or depletion. There was no evidence for volume alterations in the intracellular fluid (ICF = TBW - ECF). We conclude that the ISF is the buffer zone which maintains the proper balance and relationship between vascular capacity and volume.