Abstracts Health Sciences

The control of interdialytic weight gain in hemodialysis patients

by Alison Jane Rigby-Mathews

Background. The control of interdialytic weight gain (IDWG) is critically important in the management of hemodialysis (HD) patients, since large IDWG makes it difficult to be removed during the limited hours on hemodialysis. HD patients are constantly asked to limit their fluid intake which they are unable to do because the thirst is overwhelming. We propose that ingested sodium is the principal factor that determines the severity of thirst and consequently IDWG, and its restriction not fluid restriction should be emphasized.Methods. To test this hypothesis a prospective randomized cross-over design study was conducted in 28 adult maintenance hemodialysis subjects from three outpatient dialysis units of the Northwest Kidney Centers. Patients were randomized to the order of ingesting a very low sodium diet (less than 1 g/day) in between two dialysis treatments or their usual standard diet and fluid intake. Patients were instructed not to limit water intake when on the low sodium diet. Pre and post dialysis weights and blood samples were obtained during the study period to assess changes in body weight and changes in serum chemical composition. Food records were kept to determine intake of key nutrients, including sodium during the study period. Thirst was assessed using a visual analogue scale, immediately following the low sodium diet intervention and control periods prior to hemodialysis.Results. Despite no water restriction IDWG of the patients when they were on the low sodium diet was significantly lower than on their regular diet (1.95 +/- 1.06 Vs 2.78 +/- 1.11 kg respectively, p < 0.001). The patients also had significantly lower increases in calculated extracellular fluid volume (ECV) on the low sodium diet compared to the control period (0.77 +/- 0.97 Vs 2.21 +/- 0.99 L respectively, p < 0.001), and significantly less thirst (3.5 +/- 2.7 Vs 5.6 +/- 2.2 cm respectively, p = 0.002).Conclusions. The results demonstrate that sodium intake rather than fluid intake is the principal factor that controls IDWG. It is felt that limiting fluid intake is futile due to the overwhelming effect of thirst. Limiting dietary sodium intake may be more effective than limiting fluid intake in controlling IDWG for patients who experience excessive IDWG. These results demonstrate that the primary factor responsible for IDWG is sodium intake not fluid intake; and instruction to restrict sodium would be more effective.