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

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 Since fluid is initially withdrawn from the intravascular compartment, blood volume will decrease rapidly.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 post-dialytic 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. The seven hypotensive episodes that occurred 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 preceding the event, when compared with the data of 30 non-hypotensive controls at comparable moments of time. These results suggest that continuous 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 factor in BV preservation