Non-invasive monitoring of blood volume during hemodialysis: its relation with post-dialytic dry weight.

Hemodialysis has a profound effect on fluid balance. Since fluid is initially withdrawn from the intravascular compartment, blood volume will decrease rapidly. A fluid shift (refill) from the overhydrated interstitium towards the intravascular compartment counteracts hypovolemia. Underestimation of postdialytic dry weight will cause interstitial dehydration and consequently a low refill capacity. This can cause hypovolemia-induced hypotension, a serious problem in the daily practice of hemodialysis: during one out of three sessions a hypotensive episode occurs. Clinical criteria to estimate post-dialytic dry weight are insensitive. We have developed non-invasive methods to estimate dry weight and changes in blood volume (BV) more accurately. The aim of this study was to investigate the relation between hydration state of the patient and changes in BV during treatment. Therefore, 37 hemodialysis patients were divided into three groups according to their post-dialytic extracellular fluid volume (EFV), which was measured by means of the non-invasive conductivity method: de- (N = 11), normo- (N = 18), and overhydrated (N = 8). Using an on-line optical reflection method, changes in BV were measured continuously during hemodialysis. BV decrease, corrected for ultrafiltration, was stronger in the dehydrated (4.4 +/- 1.5%/liter) than in the normohydrated (3.3 +/- 1.5%/liter) and overhydrated (2.7 +/- 1.9%/liter) groups. In the dehydrated group, the frequency of hypotensive episodes (48.5 +/- 20.2%) was significantly greater compared to the normohydrated (20.5 +/- 23.5%) or overhydrated (6.5 +/- 6.5%) group, P < 0.005.(ABSTRACT TRUNCATED AT 250 WORDS)