NONINVASIVE MONITORING OF BLOOD-VOLUME DURING HEMODIALYSIS - ITS RELATION WITH POST-DIALYTIC DRY-WEIGHT

Hemodialysis has a profound effect on fluid balance. Since fluid is in itially withdrawn from the intravascular compartment, blood volume wil l decrease rapidly. A fluid shift (refill) from the overhydrated inter stitium towards the intravascular compartment counteracts hypovolemia. Underestimation of post-dialytic dry weight will cause interstitial d ehydration and consequently a low refill capacity. This can cause hypo volemia-induced hypotension, a serious problem in the daily practice o f hemodialysis: during one out of three sessions a hypotensive episode occurs. Clinical criteria to estimate post-dialytic dry we ht are ins ensitive. We have developed non-invasive methods to estimate dry weigh t and changes in blood volume (BV) more accurately. The aim of this st udy was to investigate the relation between hydration state of the pat ient and changes in BV during treatment. Therefore, 37 hemodialysis pa tients 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 o verhydrated (N = 8). Using an on-line optical reflection method, chang es 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 overhy drated (2.7 +/- 1.9%/liter) groups. In the dehydrated group, the frequ ency of hypotensive episodes (48.5 +/- 20.2%) was significantly greate r compared to the normohydrated (20.5 +/- 23.5%) or overhydrated (6.5 +/- 6.5%) group, P < 0.005. The seven hypotensive episodes that occurr ed in the course of the study were all characterized by a lower BV at that moment, and a greater reduction in BV during the 10 minutes prece ding the event, when compared with the data of 30 non-hypotensive cont rols at comparable moments of time. These results suggest that continu ous monitoring of changes in BV will assist in the early detection of hypovolemia, especially in dehydrated patients. Tissue hydration state can be assessed by means of conductivity analysis and forms a main fa ctor in BV preservation.