Factors associated with systolic hypertension in peritoneal dialysis patients

The association between office blood pressure and fluid status using bioimpedance spectroscopy in stable continuous ambulatory peritoneal dialysis patients

Background

Hypertension is common in continuous ambulatory peritoneal dialysis (CAPD) patients. It remains to be determined the extent to which fluid overload contributes to uncontrolled blood pressure (BP) in this population. The aim was to determine the association between fluid status as measured using bioimpedance spectroscopy (BIS) and BP in CAPD patients.

Methods

A cross-sectional study was performed involving 50 stable CAPD patients at a single center in Cape Town, South Africa. All participants were known to have hypertension and were divided into two groups based on office BP measurements: an uncontrolled BP group (systolic BP ≥ 140 mmHg or diastolic BP ≥ 90 mmHg) and a controlled BP group. Fluid status was determined using BIS (Body Composition Monitor®, Fresenius Medical Care, Bad Homburg, Germany).

Results

There was a statistically significant difference in overhydration (OH) between the uncontrolled BP group and the controlled BP group (3.0 ± 2.3 L vs. 1.4 ± 1.6 L, respectively, P = 0.01). The uncontrolled BP group was older (37.7 ± 9.5 years vs. 32.0 ± 8.0 years, P = 0.04) and had a shorter dialysis vintage (15 [IQR, 7–22] months vs. 31 [IQR, 12–39] months, P = 0.02). Significant correlations were found between OH and the extracellular water (ECW) (r = 0.557, P < 0.01) and ECW to total body water (TBW) ratio (r = 0.474, P < 0.01). Mixed ancestry, presence of residual kidney function, ECW, and ECW to TBW ratio were identified as predictors of OH on multivariable linear regression.

Conclusions

We found that stable CAPD patients with uncontrolled BP had higher OH compared to patients whose BP was controlled.

Sodium toxicity in peritoneal dialysis: mechanisms and "solutions"

The major trials in peritoneal dialysis (PD) have demonstrated that increasing peritoneal clearance of small solutes is not associated with any advantage on survival, whereas sodium and fluid overload heralds higher risk of death and technique failure. On the other hand, higher sodium and fluid overload due to loss of residual kidney function (RKF) and higher transport membrane is associated with poor patient and technique survival. Recent experimental studies also show that, independently from fluid overload, sodium accumulation in the peritoneal interstitium exerts direct inflammatory and angiogenetic stimuli, with consequent structural and functional changes of peritoneum, while in patients with Chronic Kidney Disease sodium stored in interstitial skin acts as independent determinant of left ventricular hypertrophy. Noteworthy, this tissue pool of sodium is modifiable being removed by dialysis. Therefore, novel PD strategies to optimize sodium removal, including the use of bimodal and/or low-sodium solutions, are actively tested. Nonetheless, a holistic approach aimed at preserving peritoneal function and the kidney may represent the key of therapy success in the hard task of preserving adequate sodium balance in PD patients. In this review, we describe the available evidence on sodium toxicity in PD, either related or unrelated to fluid overload, and we also discuss about possible "solutions" to preserve or restore sodium balance in PD patients.

Aortic Pulse Wave Velocity in Peritoneal Dialysis Patients Is Not Simply Associated with Extracellular Water Expansion

BACKGROUND

Cardiac death is increased in peritoneal dialysis (PD) patients. Pulse wave velocity (PWV) is a measurement of arterial stiffness, and previous reports linked PWV to increased extracellular water (ECW). As cyclers and icodextrin are increasingly used, we wished to determine whether this association between PWV and ECW remains.

METHODS

We measured aortic PWV (aPWV) and bioimpedance (InBody, Seoul, South Korea) in consecutive PD patients attending for peritoneal membrane testing.

RESULTS

189 patients were included, 62.4% male, mean age 63.1 ± 15.2 years, 45.3% diabetic, median dialysis duration 12.3 (6.5-25.1) months, 71.4% using cyclers, weight 73.0 ± 16.1 kg, systolic blood pressure 142 ± 21 mm Hg, aPWV 10.4 ± 5.1 m/s. aPWV was associated with pulse pressure (r = 0.26, p = 0.001), Davies comorbidity score (r = 0.18, p = 0.013), and N-terminal pro-brain-type natriuretic peptide (NTproBNP; r = 0.18, p = 0.011). Patients with aPWV ≥10 m/s were older (65.9 ± 13.6 vs. 60.1 ± 16.3 years, p < 0.01) with a higher ECW-to-total body water ratio (0.400 ± 0.012 vs. 0.396 ± 0.013, p < 0.05), but ECW/height was not different (8.52 ± 2.32 vs. 8.75 ± 1.78 L/m), as was NTproBNP (2,472 [788-5,422] vs. 1,234 [410-6,230] ng/L). On multivariable testing, aPWV was positively associated with β-blocker prescription (standardised β coefficient [Stβ] 0.3, 95% confidence limits [95% CL] 0.7-2.6, p = 0.001) and negatively with icodextrin prescription (Stβ 0.19, 95% CL -0.2 to -2.1, p = 0.04).

CONCLUSIONS

Compared to previous studies, we did not find an independent association between aPWV and ECW and estimates of ECW excess, using the InBody bioimpedance device, suggesting that vascular stiffness in PD patients is more complex than simple ECW volume expansion in PD patients.