Living on chronic hemodialysis between dryness and fluid overload.

The hydration state of a hemodialysis patient reflects the balance between fluid overload, normovolemia and underhydration. Since chronic volume overload enhances the cardiac mortality, and chronic underhydration carries the risk for dialysis-associated hypotension, treatment for the deranged water homeostasis of hemodialysis patients needs to focus on an accurate assessment of dry body weight. Non-invasive methods such as echocardiography of the inferior caval vein diameter (ICVD) or conductivity measurements are considered as reliable techniques to estimate the hydration state of hemodialysis patients. The value of biochemical parameters for an adequate assessment of dry body weight remains controversial. In our study we have determined cyclic guanosine 3'5'-monophosphate (cGMP) serum levels in 125 patients undergoing regular hemodialysis. Predialytic cGMP significantly decreased from 46.1 +/- 26.0 to 17.0 +/- 9.3 pmol/liter post-dialysis (P < 0.001). In 35 patients cGMP level after hemodialysis remained > 20 pmol/liter, but non of these patients displayed any clinical signs of fluid overload. In a group of patients with normal heart function (N = 29) additional sonography of the ICVD revealed normovolemia in 16 patients, underhydration in 5 patients and fluid overload in 4 patients. The respective post-dialytic mean cGMP level was significantly higher in the overhydrated group compared to normovolemic and underhydrated patients (25.3 +/- 10.8 vs. 14.7 +/- 6.4 and 11.4 +/- 5.3 pmol/liter, P < 0.02). However, there was no significant correlation between cGMP level and ICVD (r = 0.5, NS). We conclude that there is no single parameter to define the adequate dry body weight of a hemodialysis patient. Our own data demonstrate the limitations using cGMP, particularly in estimating underhydration. ICVD and bioimpedance offer non-invasive methods for both volume overload and underhydration, and seem to be reliable in the routine assessment of dry body weight.