Assessing Extracellular Volume in Hemodialysis Patients Using Intradialytic Blood Pressure Slopes

Epidemiology, Pathophysiology, and Clinical Perspectives of Intradialytic Hypertension

BACKGROUND

Individuals with end-stage renal disease on chronic hemodialysis (HD) may encounter numerous HD-associated complications, including intradialytic hypertension (IDHYPER). Although blood pressure (BP) follows a predictable course in the post-HD period, BP levels during the session may vary across the individuals. Typically, a decline in BP is noted during HD, but a significant proportion of patients exhibit a paradoxical elevation.

SUMMARY

Several studies have been conducted to understand the complexity of IDHYPER, but much remains to be elucidated in the future. This review article aimed to present the current evidence regarding the proposed definitions, the pathophysiologic background, the extent and clinical implications of IDHYPER, as well as the possible therapeutic options that have emerged from clinical studies.

KEY MESSAGES

IDHYPER is noted in approximately 15% of individuals undergoing HD. Several definitions have been proposed, with a systolic BP rise >10 mm Hg from pre- to post-dialysis in the hypertensive range in at least four out of six consecutive HD treatments being suggested by the latest Kidney Disease: Improving Global Outcomes. Concerning its pathophysiology, extracellular fluid overload is a crucial determinant, with endothelial dysfunction, sympathetic nervous system overdrive, renin-angiotensin-aldosterone system activation, and electrolyte alterations being important contributors. Although its association with ambulatory BP in the interdialytic period is controversial, IDHYPER is associated with adverse cardiovascular events and mortality. Moving to its management, the antihypertensive drugs of choice should ideally be nondialyzable with proven cardiovascular and mortality benefits. Finally, rigorous clinical and objective assessment of extracellular fluid volume is essential. Volume-overloaded patients should be instructed about the importance of sodium restriction, while physicians ought to alter HD settings toward a greater dry weight reduction. The use of a low-sodium dialysate and isothermic HD could also be considered on a case-by-case basis since no randomized evidence is currently available.

Comparative Impact of Isolated Ultrafiltration and Hemodialysis on Fluid Distribution: A Bioimpedance Study

INTRODUCTION

Isolated ultrafiltration (IUF) is an alternative treatment for diuretic-resistant patients with fluid retention. Although hemodialysis (HD) predominantly decreases extracellular water (ECW), the impact of IUF on fluid distribution compared with HD remains unclear.

METHODS

We compared the effect of HD (n = 22) and IUF (n = 10) sessions on the body fluid status using a bioimpedance analysis device (InBody S10).

RESULTS

The total ultrafiltration volume was similar between HD and IUF (HD 2.5 ± 0.3 vs. ICF 2.1 ± 0.3 L/session, p = 0.196). The reduction rate of ECW was significantly higher than that of intracellular water (ICW) after HD (ECW -7.9% ± 0.8% vs. ICW -3.0% ± 0.9%, p < 0.001) and IUF (ECW -5.8% ± 0.9% vs. ICW -3.6% ± 0.8%, p = 0.048). However, the change in the ratio of ECW to total body water in HD was significantly larger than that in IUF (HD -3.2% ± 0.3% vs. ICF -1.1% ± 0.4%, p < 0.001). The reduction rates in serum tonicity (effective osmolality) were higher after HD than after IUF (HD -1.8% ± 0.5% vs. IUF -0.6% ± 0.2%, p = 0.052). Among the components of effective osmolality, the reduction rates of serum K+ and glucose levels after HD were significantly higher than those after IUF (serum K+: HD -30.5% ± 1.6% vs. IUF -0.5% ± 3.8%, p < 0.001; serum glucose: HD -15.4% ± 5.0% vs. IUF 0.7% ± 4.8%, p = 0.026), while the serum Na+ level was slightly and similarly reduced (HD -0.8% ± 0.4% vs. IUF -0.8% ± 0.4%, p = 0.500). The reduction in the osmolal gap value (measured osmolality-calculated osmolarity) was significantly greater after HD sessions than after IUF sessions (HD -12.4 ± 1.4 vs. IUF 2.0 ± 1.0 mOsm/kg, p = 0.001).

CONCLUSION

The extracellular fluid reduction effect of HD is stronger than that of IUF. The different changes in effective osmolality and osmolal gap after HD and IUF sessions may be related to the different effects of HD and IUF on fluid distribution.

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 (β = 133, P = 0.01; n = 52) and ambulatory BP slope (β = −4.28, P = 0.03; n = 42). ECV/weight was associated with mean ambulatory BP in those with recurrent IH (β = 314, P = 0.0005; n = 16) and with ambulatory BP slope in those without recurrent IH (β = −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.