Osmotic disequilibrium causing ascites during chronic hemodialysis

Ascites formation is a recognized complication of chronic hemodialysis (CHD). The cause is an enigma after tumors, tuberculosis, and heart, liver, and pancreatic diseases are excluded. A 55-year-old patient who developed intractable ascites about 6 months after starting CHD was studied. The premise was that osmotic disequilibrium during HD may be the causative factor. Other causes of ascites were excluded. The study method relied on determining simultaneous serum and ascites osmolality (Sosm and Aosm) at the start and finish of a standard 4 hour HD session.

Sosm and Aosm at the start averaged 310 and 309 mosm/L, respectively. At the end, Sosm averaged 285 and Aosm averaged 301 mosm/L, giving a 16 mosm concentration gradient. Two days later, Sosm and Aosm were equal again. It is concluded that the osmotic gradient at the end of 4 hours of HD favors movement of water from the intravascular space into the ascitic fluid space until osmotic equilibrium is once again achieved.