Association between Brain Natriuretic Peptide and Extracellular Water in Hemodialysis Patients

Abstract

Background: Brain natriuretic peptide (BNP) is a hormone released by the left ventricle (LV) as a consequence of pressure or volume load. BNP increases in left ventricle hypertrophy (LVH), LV dysfunction, and it can also predict cardiovascular mortality in the general population as well as those undergoing hemodialysis (HD). We investigated the association between BNP and volume load in HD patients. Methods: We studied 32 HD patients (60 ± 17.1 years) treated thrice-weekly for at least 6 months. Exclusion criteria were: LV dysfunction, atrial fibrillation, malnutrition. Blood chemistries and BNP were determined on mid-week HD day. Blood pressure (BP) and cardiac diameters were determined on mid-week inter-HD day by using 24-hour ambulatory blood pressure monitoring and echocardiography. Bioimpedance was performed after HD and extracellular water (ECW%), calculated as a percentage of total body water, was considered as the index of volume load. Results: Patients were divided into quartiles of 8 patients depending on the BNP value: 1st qtl BNP ≤45.5 pg/ml (28.4 ± 10.9 pg/ml), 2nd qtl BNP > 45.5 pg/ml and ≤99.1 pg/ml (60.9 ± 15.8 pg/ml), 3rd qtl BNP > 99.1 pg/ml and ≤231.8 pg/ml (160.5 ± 51.8 pg/ml), 4th qtl BNP > 231.8 pg/ml (664.8 ± 576.6 pg/ml). No inter-quartile differences were reported in age, HD age, body mass index spKt/V, or blood chemistries. As expected patients in the 4th BNP quartile showed the highest values of 24-hour pulse pressure (PP) and LV mass index (LVMi). The study of body composition revealed significant differences in ECW%, which was higher in the 4th quartile when compared to the others (4th q: 50 ± 9.6%, vs 1st q. 40.1 ± 2.4%, 2nd q. 41.9 ± 5%, 3rd q. 42.8 ± 6.9%). Using multiple stepwise linear regression where BNP was the dependent variable, and PP and ECW% the independent variables, only ECW% maintained statistical significance as a predictor of BNP levels (PP: Beta = 0.86, p = 0.58; ECW%: Beta = 0.64, p < 0.001 p < 0.001). Conclusions: Few studies have investigated the relationship between plasma BNP and volume load, and direct evidence is lacking. We used bioimpedance and the determination of ECW% to assess volume state in HD patients finding an association between BNP and ECW. The increased synthesis and release of BNP from the LV in HD patients appear to be mainly related to volume stress rather than to pressure load.

N-terminal proBNP—Marker of Cardiac Dysfunction, Fluid Overload, or Malnutrition in Hemodialysis Patients?

“…On simple correlation analysis and in keeping with other reports, we found that NT-proBNP was associated with markers suggestive of volume overload: ultrafiltration rate, cardiothoracic ratio, predialysis ratio of extracellular water to total body water, and change in extracellular fluid volume with dialysis and postdialysis BP (4,7,12). However, there were also correlations with left ventricular diastolic dysfunction as assessed by standard two-dimensional transthoracic echocardiograms and previous history of hypertension with current prescription of beta-blockers, suggestive of an association with cardiac function and supporting previous observations (2,13).…”

“…This may be due to the different sizes and half-lives of the peptides, because ANP is cleared during high-flux hemodialysis, with a post dialysis rebound taking some 80 to 100 minutes to re-equilibrate (Mathavakkannan, unpublished data). However, others have shown higher BNP values in volume-overloaded hemodialysis patients without overt cardiac dysfunction (4). Because BNP can also be cleared by high-flux dialysis and has been shown to sequentially fall during the course of a typical dialysis week (5), there has been debate as to whether these cardiac biomarkers are more reflective of fluid volume overload or intrinsic cardiac dysfunction in hemodialysis patients.…”

N-Terminal Pro–B-Type Natriuretic Peptide Variability in Stable Dialysis Patients

“…Several factors affect NT-proBNP concentrations, including extracellular volume (12), cardiac rhythm (13), myocardial ischemia (14,15), the dialysis prescription (16), and cardiac pharmacotherapy (17)(18)(19). These influences were assessed at every visit using a structured clinical interview, physical examination, and medical records review to ascertain interim hospitalization and changes to medication and/or the dialysis prescription.…”

N‑terminal pro‑B-type natriuretic peptide as a marker of hypervolemia and predictor of increased mortality in patients on hemodialysis

“…These findings are, at least partially, in line with other studies. 20,24,25,31,32 On the other hand, Booth et al 21 was able to connect log NT-proBNP with ultrafiltration rate, whereas Nongnuch et al, …”