[Arterial hypertension in chronic kidney failure: a volume-dependent pathology or a disease due to malnutrition?]

Hemodialysis patients are a clinical circulatory model whose main feature is discontinuous fluid removal. Extracorporeal treatment in chronic renal failure exerts blood-volume and circulatory changes with effects on post-dialysis blood pressure (BP). We investigated if pre-dialysis body fluid disposition and body composition, assessed as lean and fat mass, have different relationship with blood pressure.

Bio-electrical whole-body multifrequency impedance analysis (BIA) enables dynamic assessment of body composition according to a multi-compartment model: extracellular (ECW) and total body water (TBW), lean (FFM) and fat (FAT) mass. We studied 73 patients (53 males, 20 females), mean age 54.4 +/- 13.1 years, on maintenance bicarbonate dialysis for 57.3 +/- 61.8 months. BIA was performed at the start and at the end of three consecutive dialysis sessions; blood pressure was monitored non-invasively throughout dialysis. Twenty-one patients (HP) were hypertensive (systolic BP 183.63 +/- 26.88 mmHg) and on pharmacological treatment, while 52 patients (NP) were normotensive (systolic BP 131.68 +/- 12.63 mmHg).

Pre-dialysis assessment of blood pressure (BP) and body compartment in HP showed inverse relationships between systolic BP and percentage of total body water (r = -057, p < 0.001) and between BP vs lean mass/fat mass ratio (r = -0.68, p < 0.001). A high positive correlation was observed between systolic BP and percentage of fat mass (r = 0.73, p < 0.001). At the end of dialysis session, a strong relationship was observed between systolic BP and extracellular water (r = 0.77, p < 0.001). BP changes with dialysis do not show any special correlation with body compartment changes. No significant or overly weak correlations were observed in normotensive patients.

Arterial hypertension of maintenance hemodialysis patients shows a strong relationship with the percentage of body fat and with FFM/FAT ratio, i.e. with the adiposity of diseased malnourished patients. Moreover, as suggested by the relationship between ECW and BP, present only at the end of dialysis, expansion of the extracellular water compartment or in other words, the degree of adequacy of water filtration during dialysis, seems to be an important condition in determining post-dialysis BP levels in hypertensive patients. The increase in BP during the interdialysis period is not closely interrelated with the degree of body hydration, but there is strong evidence that it is connected with the effects of malnutrition, including the increase in body lipids. This condition is multifactorial and can be a consequence of nutritional behavior, as well as of kidney disease and dialysis itself, with metabolic derangement also associated with protein and I-carnitine deficiency.