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.

Effect of indexed glomerular filtration rate according to age

BACKGROUND

To find out up to what age there is dispersion in glomerular filtration rate (GFR) values when normalised by body surface area (BSA) and extracellular fluid volume (ECFV), based on the hypothesis that these values differ in childhood age.

METHODS

A retrospective study was performed on patients aged 0-85 years, with renal pathology, who were administered i.v. 51Cr-EDTA. GFR was obtained using the Ham and Piepsz (children) or Christensen and Groth (adults) formula. Results were normalised by BSA and ECFV.

RESULTS

The cut-off point is defined as the age that discriminates between values ± 10 points apart. Using a ROC curve analysis, this age was set at 11.96 years with a sensitivity of 0.83 and a specificity of 0.85. The area obtained was 0.902 (95%CI 0.880-0.923). The results were corroborated by linear regression stratifying by age. For children under 12 years of age, the Pearson correlation was 0.883 (95% CI 0.860-0.902). For those aged 12 years or older, this coefficient was 0.963 (95%CI 0.957-0.968). According to our results, when normalising GFR by BSA and by ECFV there are different behaviours according to age.

CONCLUSION

For children older than 12 years both normalisation methods can be used, but for children younger than 12 years there are differences. We believe that in children under 12 years of age, GFR should be normalised by ECFV.

Differential assessment of fluid compartments by bioimpedance in pediatric patients with kidney diseases

BACKGROUND

The kidney is central for maintaining water balance. As a corollary, patients with impaired kidney function are prone to pathological fluid volumes. Total body water (TBW) is distributed between the extracellular (ECW) and intracellular fluid compartments (ICW). In clinical practice, the judgment of hydration status does not allow to distinguish between ECW and ICW. Here, we evaluate the hydration status in children with chronic kidney disease by analyzing TBW, ECW, and ICW.

METHODS

Hydration was quantified using whole-body bioimpedance spectroscopy (BCM) in 128 outpatients (1-25 years, 52 girls). Forty-two were transplanted (TPL), 43 suffered from chronic kidney disease without kidney replacement therapy (CKD), 21 were on peritoneal dialysis (PD), and 22 on hemodialysis (HD). HD patients were investigated before, after, and sequentially during dialysis.

RESULTS

The ECW and ICW values obtained by BCM were of the same magnitude as those from the literature using isotope dilution. When compared with a healthy control group, TBW was increased in 9 TPL, 9 CKD, 1 PD, and 11 HD patients before but in none after dialysis. The decline of overhydration during dialysis (p < 0.001, n = 22) correlated with the change in body weight (R² = 0.62). The kinetics of fluid compartment changes assessed twice in six HD patients revealed a reproducible linear decay of the ECW/ICW ratio due to an increase of ICW and a decrease of ECW.

CONCLUSION

BCM quantifies TBW and acute changes of ECW and ICW in children with chronic kidney failure. The clinical utility of measuring TBW, ECW, and ICW should be defined in the future.

[Which biological parameters for volemic status estimation?]

INTRODUCTION

Estimation of volemic status can be useful in the diagnosis of some hydro-electrolytic disorders such as hyponatremia and dyskalemia. As a matter of fact, clinical examination and classical biological parameters are not discriminant enough. The aim of this study was to determine the biological parameters that are better correlated to volemic status.

METHOD

Volemic status was established using extracellular fluid volume, measured by apparent distribution of inuline, in non-edematous patients and without cardiac or hepatic insufficiency. Patients were split in three groups according to their extracellular fluid volume: hypovolemic, normovolemic, and hypervolemic. Clinical and biological parameters were compared between the three groups and were correlated to extracellular fluid volume.

RESULTS

Data of 91 explorations were collected. There were no difference between groups regarding clinical parameters, plasma proteins, and urinary sodium excretion. Parameters better correlated to extracellular fluid volume were fasting calcium/creatinine ratio (r=0.51; P<0.0001), fasting urinary pH (r=0.43; P<0.0001), and plasma uric acid (r=-0.39; P=0.002).

CONCLUSION

In addition to uric acid, already proposed as a biological marker to estimate volemic status, fasting calciuria and fasting urinary pH could also be useful.

Fluid volume expansion and depletion in hemodialysis patients lack association with clinical parameters

BACKGROUND

Achievement of normal volume status is crucial in hemodialysis (HD), since both volume expansion and volume contraction have been associated with adverse outcome and events.

OBJECTIVES

The objectives of this study are to assess the prevalence of fluid volume expansion and depletion and to identify the best clinical parameter or set of parameters that can predict fluid volume expansion in HD patients.

DESIGN

This study is cross-sectional.

SETTING

This study was conducted in three hemodialysis units.

PATIENTS

In this study, there are 194 HD patients.

METHODS

Volume status was assessed by multifrequency bio-impedance spectroscopy (The Body Composition Monitor, Fresenius) prior to the mid-week HD session.

RESULTS

Of all patients, 48 % (n = 94) were volume-expanded and 9 % of patients were volume-depleted (n = 17). Interdialytic weight gain was not different between hypovolemic, normovolemic, and hypervolemic patients. Fifty percent of the volume-expanded patients were hypertensive. Paradoxical hypertension was very common (31 % of all patients); its incidence was not different between patient groups. Intradialytic hypotension was relatively common and was more frequent among hypovolemic patients. Multivariate regression analysis identified only four predictors for volume expansion (edema, lower BMI, higher SBP, and smoking). None of these parameters displayed both a good sensitivity and specificity.

LIMITATIONS

The volume assessment was performed once.

CONCLUSIONS

The study indicates that volume expansion is highly prevalent in HD population and could not be identified using clinical parameters alone. No clinical parameters were identified that could reliably predict volume status. This study shows that bio-impedance can assist to determine volume status. Volume status, in turn, is not related to intradialytic weight gain and is unable to explain the high incidence of paradoxical hypertension.

Hyponatremia in the intensive care unit: How to avoid a Zugzwang situation?

Hyponatremia is a common electrolyte derangement in the setting of the intensive care unit. Life-threatening neurological complications may arise not only in case of a severe (<120 mmol/L) and acute fall of plasma sodium levels, but may also stem from overly rapid correction of hyponatremia. Additionally, even mild hyponatremia carries a poor short-term and long-term prognosis across a wide range of conditions. Its multifaceted and intricate physiopathology may seem deterring at first glance, yet a careful multi-step diagnostic approach may easily unravel the underlying mechanisms and enable physicians to adopt the adequate measures at the patient’s bedside. Unless hyponatremia is associated with obvious extracellular fluid volume increase such as in heart failure or cirrhosis, hypertonic saline therapy is the cornerstone of the therapeutic of profound or severely symptomatic hyponatremia. When overcorrection of hyponatremia occurs, recent data indicate that re-lowering of plasma sodium levels through the infusion of hypotonic fluids and the cautious use of desmopressin acetate represent a reasonable strategy. New therapeutic options have recently emerged, foremost among these being vaptans, but their use in the setting of the intensive care unit remains to be clarified.

Adiposity has unique influence on the renin-aldosterone axis and blood pressure in black children

OBJECTIVE

To comparatively examine the effects of adiposity on the levels of plasma renin activity (PRA), plasma aldosterone concentration (PAC), and aldosterone-renin ratio (ARR) in young black and white children.

STUDY DESIGN

We prospectively assessed 248 black and 345 white children and adolescents. A novel analytical technique was used to assess the concurrent influences of age and body mass index (BMI) on PRA, PAC, and ARR. The estimated effects were depicted by colored contour plots.

RESULTS

In contrast to whites, blacks had lower PRA (2.76 vs 3.36 ng/mL/h; P < .001) and lower PAC (9.01 vs 14.59 ng/dL; P < .001). In blacks, BMI was negatively associated with PRA (P = .001), consistent with an association with a more expanded plasma volume; there was no association with PAC. In whites, BMI was positively associated with PAC (P = .005); we did not detect a BMI-PRA association. The effects of BMI on ARR were directionally similar in the two race groups but more pronounced in blacks. Mean systolic blood pressure was greater in blacks with lower PRA (P < .01), higher PAC (P = .015), and higher ARR (P = .49).

CONCLUSIONS

An increase in adiposity was associated with a suppressed PRA in blacks and an increase in PAC in whites. The unique relationship between adiposity and renin-aldosterone axis in blacks suggests the possible existence of a population-specific mechanism characterized by volume expansion, which could in turn enhance the influences of adiposity on blood pressure in black children and adolescents.