The understanding of fluid changes during hemodialysis (HD is essential for reducing complications as well as efficacy of the procedure. Bioimpedance spectroscopy provides a non invasive method of measuring total body water (TBW), the distribution of intra (ICF) and extracellular (ECF) fluids, and their changes during HD. Segmental bioimpedance may be used to measure the same fluid shifts but from different body segments; the technique has previously been shown to com pare well with whole body measures. It is possible that fluid shifts occur differently in different body compartments during HD. Based on previous hemodynamic studies we postulated that during HD ultrafiltration (UF) the body attempts to preserve its central blood volume (cardiopulmonary circula tion plus great vessels), and thus fluid shifts would be greater from the periphery than from central compartments. To test this hypothesis, segmental bioimpedance (Xitron Technolo gies, San Diego, CA) was performed on 11 subjects undergoing HD where ECF and ICF values were obtained from the legs, arms and trunk before and after a period of UF. Blood volume change (ABV%) was also followed using an on-line optical hematocrit (Hct) sensor (Crit-Line monitor, In-Line Diagnostics, UT) where deltaBV% = deltaBV% = (1 - Hct1/Hct0) x 100 (Hct0 = baseline Hct; Hct1 = postultrafiltration Hct) The UF of 2.0 L +/- 0.79 L (M +/- SD) over 75 minutes was associated with a deltaBV% of -9.43% +/- 3.6% (M +/- SD), a significant (Student's paired t-test) reduction in total body (TB) ECF (p < 0.02), a weak correlation in reduction in TBW (p = 0.09) but not in TB ICF. The ECF reductions from the trunk, legs, and arms were all significant (minimum p < 0.02); no ICF changes from these compartments were significant. The amount of ECF reduction was greater from the legs (0.7 L +/- 0.6 L) than the arms (0.12 L +/- 0.08 L) and trunk (0.2 L +/- 0.2 L) (all M +/- SD). Multiple regression analysis showed that TB ECF changes correlated strongly with leg (r = 0.94, p < 0.001) and arm (r = 0.72, p = 0.002) ECF changes but not with trunk changes. deltaBV% correlated weakly with leg (r = 0.45, p = 0.08) and arm (r = 0.42, p = 0.10) ECF changes but not with the trunk. As the deltaBV% represents the net volume change between UF and plasma water refilling, thiss indicates that plasma water is being removed more from the peripheral compartments than from the trunk. These data suggest that plasma refilling during HD to preserve central blood volume is more dynamic from the leg ECF than from elsewhere and may, in turn, explain the frequent occurrence of leg cramps during and after hemodialysis.

No abstract

Background: Small randomized trials demonstrated that a lower compared with higher dialysate temperature reduced the average drop in intradialytic blood pressure. Some observational studies demonstrated that a lower compared with higher dialysate temperature was associated with a lower risk of all-cause mortality and cardiovascular mortality. There is now the need for a large randomized trial that compares the effect of a low vs high dialysate temperature on major cardiovascular outcomes. Objective: The purpose of this study is to test the effect of outpatient hemodialysis centers randomized to (1) a personalized temperature-reduced dialysate protocol or (2) a standard-temperature dialysate protocol for 4 years on cardiovascular-related death and hospitalizations. Design: The design of the study is a pragmatic, registry-based, open-label, cluster randomized controlled trial. Setting: Hemodialysis centers in Ontario, Canada, were randomized on February 1, 2017, for a trial start date of April 3, 2017, and end date of March 31, 2021. Participants: In total, 84 hemodialysis centers will care for approximately 15 500 patients and provide over 4 million dialysis sessions over a 4-year follow-up. Intervention: Hemodialysis centers were randomized (1:1) to provide (1) a personalized temperature-reduced dialysate protocol or (2) a standard-temperature dialysate protocol of 36.5°C. For the personalized protocol, nurses set the dialysate temperature between 0.5°C and 0.9°C below the patient’s predialysis body temperature for each dialysis session, to a minimum dialysate temperature of 35.5°C. Primary outcome: A composite of cardiovascular-related death or major cardiovascular-related hospitalization (a hospital admission with myocardial infarction, congestive heart failure, or ischemic stroke) captured in Ontario health care administrative databases. Planned primary analysis: The primary analysis will follow an intent-to-treat approach. The hazard ratio of time-to-first event will be estimated from a Cox model. Within-center correlation will be considered using a robust sandwich estimator. Observation time will be censored on the trial end date or when patients die from a noncardiovascular event. Trial Registration: www.clinicaltrials.gov ; identifier: NCT02628366.

Predialysis ECF influences BP and UF reduces DeltaBV and ECF, but CBV and BP are conserved by increasing PVR. ECF reduction is mainly from the legs, hence may cause cramps. Intradialytic hypotension is caused by failure of PVR response.