Intradialytic alkalinization is a neglected factor affecting calcium mass balance and parathyroid hormone level during haemodiafiltration.

BACKGROUND: The diffusion gradient between ionized calcium (iCa) in the inlet dialysate and blood is considered to be the main driving force of calcium mass balance (CMB). The intradialytic change of parathyroid hormone (PTH) level corresponds to the change in plasma iCa. In contrast to the widely discussed calcium concentration of dialysis solution, the dialysate pH and bicarbonate concentration (DHCO3), important factors affecting the level of iCa, have not been studied with respect to the intradialytic change of plasma PTH level (ΔPTH) and CMB. METHODS: We measured ΔPTH and CMB (calcium flux from the dialysate to the patient) in 10 stable patients on haemodiafiltration. All patients underwent two treatments differing in DHCO3 (26 versus 32 mmol/L). The dialysate calcium concentration was 1.25 mmol/L for all treatments. RESULTS: We found significant difference in ΔPTH, which decreased with 26_DHCO3 and slightly increased with 32_DHCO3 (-110.5 versus +19.7 pg/mL, P < 0.01). CMB was negative for both DHCO3, but with higher DHCO3 there was a trend to minor intradialytic loss of calcium (-108 versus -309 mg). CONCLUSIONS: DHCO3 increase at first glance leads to contrasting phenomena: the intradialytic rise of PTH and calcium gain. Both processes are caused by a pH-dependent decrease of plasma iCa, resulting in parathyroid stimulation and intradialytic increase of iCa diffusion gradient. We found no significant correlation between CMB and intradialytic change of plasma total Ca. With respect to plasma PTH level and CMB, the bicarbonate concentration should always be taken into account when selecting the optimal dialysis solution.

[Metabolic acidosis in chronic kidney disease]. / Metabolická acidóza u chronického onemocnení ledvin.

Metabolic acidosis (MAC) is a constant symptom of chronic kidney disease (CKD) in advanced stages. However, its onset and degree do not depend only on the decrease of glomerular filtration but also on tubular functions. Therefore, in patients with predominant tubulointerstitial involvement it may already appear in earlier stages of CKD, usually as MAC with normal anion gap. The progressive decrease of glomerular filtration leads to acid retention that develops in a MAC with an increased anion gap. MAC has many adverse clinical impacts, including the progression of the underlying CKD. The development and degree of MAC in CKD is usually influenced by a combination of several pathophysiological mechanisms and a number of external factors, the most important of them being the diet - the intake and type of proteins - and hydration status. A correct identification of the factors contributing to MAC determines the therapeutic possibilities of its correction. However, optimal serum concentrations of bicarbonate in conservatively treated patients are still subject to debate. Opinions are even more divided on the question of optimal serum concentration of bicarbonate before and after dialysis, in particular due to the risk of post-dialysis meta-bolic alkalosis.Key words: dialysate bicarbonate - chronic kidney disease - metabolic acidosis - sodium bicarbonate - sodium-chloride difference.

Acid-base disorders associated with serum electrolyte patterns in patients on hemodiafiltration.

BACKGROUND: Metabolic acidosis (MAC) is a common aspect of dialysis-dependent patients. It is definitely caused by acid retention; however, the influence of other plasma ions is unclear. Understanding the mechanism of MAC and its correction is important when choosing the dialysis solution. Therefore, we assessed the relationship between intradialytic change of acid-base status and serum electrolytes. METHODS: We studied 68 patients on post-dilution hemodiafiltration, using dialysate bicarbonate concentration 32mmol/L. The acid-base disorders were evaluated by the traditional Siggaard-Anderson and modern Stewart approaches. RESULTS: The mean pre-dialysis pH was 7.38, standard base excess (SBE) -1.5, undetermined anions (UA(-)) 7.5, sodium-chloride difference (Diff(NaCl)) 36.2mmol/L. MAC was present in 34% of patients, of which 83% had an increased UA(-) as a major cause of MAC. The mean nPCR was 0.99g/kg/day and correlated negatively with SBE. After dialysis, metabolic alkalosis predominated in 81%. The mean post-dialysis pH was 7.45, SBE 4, UA(-) 2.6, Diff(NaCl) 36.9mmol/L. ΔSBE significantly correlated with ΔUA(-), but not with ΔDiff(NaCl) or ΔCl(-). CONCLUSIONS: MAC in patients on hemodiafiltration is mainly caused by acid retention and is associated with higher protein intake. We did not prove the effect of sodium or chloride on acid-base balance. Even though we used a relatively low concentration of dialysate bicarbonate, we recorded a high proportion of post-dialysis alkalosis caused by the excessive decrease of undetermined anions, which had been completely replaced by bicarbonate and indicated the elimination of undesirable anions, as well as of normal endogenous anions.

Ghrelin variants influence development of body mass index and plasma levels of total cholesterol in dialyzed patients.

BACKGROUND: Ghrelin is an endogenous hormone expressed predominantly in the stomach. Ghrelin controls growth hormone secretion and also affects the body's energy balance. We analyzed the association of ghrelin variants with body mass index (BMI), albumin as a marker of malnutrition and plasma lipids as risk factors for atherosclerosis in hemodialyzed patients, in whom malnutrition and accelerated atherosclerosis are common complications. METHODS: Ghrelin variants Arg51>Gln and Leu72> Met were analyzed by PCR-RFLP in 210 hemodialyzed patients, prospectively followed up for 15 months. Changes in body mass index, triglycerides, total cholesterol and albumin over time (after 3, 6, 9, 12 and 15 months of dialysis) were analyzed in subgroups divided according to ghrelin genotypes. RESULTS: Carriers of at least one of the Gln51 and Met72 alleles lost body weight more quickly than Arg51Arg/Leu72Leu homozygotes (p<0.01). Carriers of the Gln51 allele were at higher risk of developing high cholesterol levels (p<0.01). CONCLUSIONS: Common ghrelin variants may have an effect on changes in biochemical and anthropometric parameters in hemodialyzed patients over time and could be used in the future to plan individualized therapy.