#500 Monitoring relative blood volume and calf bioimpedance in hemodialysis patients
Authors: Sipahioglu Murat , Liu L I , Raimann Jochen , Mermelstein Ariella , Levin Nathan W , Kotanko Peter , Zhu Fansan 
Published: May 2024

Abstract

Background and Aims
Measurements of relative blood volume (RBV, %) are used to monitor the relative change in blood plasm during hemodialysis (HD). Continuous measurement of calf extracellular volume (cECV) during HD allows the calculation of relative change in cECV (RCE). RCE was defined as the ratio of cECV to its initial value, cECV0 (RCE = 100 × cECV/cECV0, %). The aim of our study was to investigate the relationship between RBV, RCE and the occurrence of intradialytic hypotension (IDH).

Method
Fifty-five HD patients were studied. We reduced the HD target weight stepwise by 0.1 to 0.2 kg per HD session until clinically defined IDH symptoms occurred. RBV was monitored using the blood volume monitor (BVM, Fresenius Medical Care, Germany). Whole body bioimpedance spectroscopy (wBIS) provided whole body ECV (wECV) and intracellular volume (wICV) pre and post HD. Continuous calf bioimpedance (Hydra 4200, Xitron Technologies, San Diego, CA USA) provided cECV during HD. Pre HD overhydration (OH) was calculated according to whole body composition model (Chamney et al, Am J Clin Nutr 2007; 85:80). Total number of HD sessions in all patients were divided into three groups according to the pre HD OH: 1) normal OH (NOH, OH &lt; 1 L), 2) moderate OH (MOH, 1 ≤ OH &lt; 4 L) and 3) severe OH (SOH, OH ≥ 4 L). Furthermore, patients were stratified by the presence or absence of IDH in each hydration group. Ultrafiltration rate (UFR), pre HD body weight, body mass index (BMI) were measured. Minimal RBV (RBVMin) and minimal RCE (RCEMin) in each HD session were recorded. These measures represent maximum reduction of fluid in the intravascular and interstitial spaces, respectively. Reducing cECV can be considered as refilling fluid from interstitial transferring to intravascular space driving by ultrafiltration. The difference between RCEMin and RBVMin was defined as vascular refilling capacity. Linear mixed-effect logistic regression (LMELR) analysis was applied to explore relationships between IDH with RBVMin, RCEMin, wECV and BMI.

Results
We studied 621 HD sessions in 55 patients. MOH was present in 57%, SOH in 22% and NOH in 21% of total number of HD sessions respectively. There were significant differences in age, UFR, RBVMin, RCEMin, pre HD wECV, BMI between three groups, while the IDH rate did not differ significantly (Table 1). RBVMin was inversely correlated with UFR (Fig. 1) in all measurements. Pre HD wECV was the only factor associated with IDH in overall measurement. Pre HD wECV was significantly lower in IDH than in non-IDH patients in the NOH group (Fig. 2). In the MOH group, UFR and RCEMin-RBVMin were higher in IDH than in non-IDH patients (Fig. 3a and Fig. 3b). In the SOH group, Pre HD OH is the major factor associated with IDH (Fig. 4).

Conclusion
This study found that the major factors leading to IDH are 1) lower hydration status; 2) relative higher UFR; and 3) the limited refilling capacity. RBVMin correlated with UFR, but it did not predict IDH. Combined analysis of RBV and calf bioimpedance may provide a means to quantitate the fluid transport between intravascular and interstitial compartments and could add to an early IDH warning system.