The effects of extracellular volume and intradialytic peripheral resistance changes on ambulatory blood pressure in hemodialysis patients with and without recurrent intradialytic hypertension

Background. Hypertension and extracellular volume (ECV) overload are interrelated mortality risk factors in hemodialysis (HD) patients, but confounding related to changes in ECV and vasoconstriction during and between treatments obfuscate their relationship. We sought to clarify independent contributions of post-HD ECV and intradialytic changes in vasoconstriction on ambulatory blood pressure (BP) in patients with and without recurrent intradialytic hypertension (IH). Methods. In this prospective observational study, we obtained measurements of pre- and post-HD ECV with bioimpedance spectroscopy (BIS), pre- and post-HD total peripheral resistance index and 44-h ambulatory BP. Linear regression determined associations between post-HD ECV/weight and intradialytic change in total peripheral resistance index (TPRI) with interdialytic BP and slope. Results. In fully-adjusted models for participants with complete data, post-HD ECV/weight associated with mean ambulatory BP (beta=133, P=0.01; n=52) and ambulatory BP slope (beta= -4.28, P=0.03; n=42). ECV/weight was associated with mean ambulatory BP in those with recurrent IH (beta=314, P=0.0005; n=16) and with ambulatory BP slope in those without recurrent IH (beta=-4.56, P=0.04; n=28). Interdialytic weight gain percentage and intradialytic TPRI change were not associated with ambulatory BP or slope in any analyses. Conclusion. Ambulatory BP in HD patients is more strongly associated with post-HD ECV assessed with BIS than with intradialytic TPRI changes or interdialytic ECV increases. These findings highlight the essential role of recognizing and managing chronic ECV overload to improve ambulatory BP in HD patients, particularly so for those with IH.