F. Locatelli

Intradialytic Calcium Balances with Different Calcium Dialysate Levels

It has been shown that calcium carbonate (CaCO3) is an effective phosphate binder which is less toxic than Al(OH)3. However, given that its use with standard calcium dialysate (CaD) levels may lead to hypercalcemia, a decrease in CaD levels has been proposed. The aim of the present study was to elevate the acute clinical and biochemical consequences of a lowering of CaD in HD patients. Dialysate composition was otherwise the same. (1) Blood pressure levels (BP) during short hemodialysis were measured in a group of 12 patients who underwent alternate hemodialyses with dialysate calcium of 1.75 and 1.25 mmol/l. (2) Ca2+ and PTH kinetics during short hemodialysis were studied in a group of 6 patients who were sequentially treated with 1.75 and 1.25 mmol/l CaD. The results show: (1) that cardiovascular stability in chronic HD patients during short HD sessions with low CaD (LCaD) may be good; (2) that a single treatment with standard CaD (SCaD) produces positive calcium balances (JCa2+) with Ca2+ plasma increase and PTHi inhibition at the end of HD sessions; during HD with LCaD there were neutral mean JCa2+ and no changes in post-dialysis mean Ca2+ and PTHi plasma levels; furthermore 2 patients showed a small PTHi increase during HD with LCaD and neutral JCa2+ because of a high positive bicarbonate balance during HD. In conclusion, as with several aspects of dialysis treatment, dialysate calcium levels should also be individualized to avoid hypercalcemic crises or PTHi stimulation.

Determining the Adequacy of Sodium Balance in Hemodialysis Using a Kinetic Model

The importance of sodium balance avoiding intradialytic cardiovascular instability and interdialytic hypertension and pulmonary edema is well known. An early analytical single-pool kinetic model created to evaluate sodium balance in hemodialysis, using flame photometry to determine plasma and dialysate sodium concentrations, has been shown to have a level of imprecision of +/- 2.8 mEq/l in predicting end-dialysis sodium plasma water concentrations (NaPWt). The ionometric determination of sodium concentrations seems to be more accurate and refers to the activity of the sodium capable of crossing dialysis membranes. On the basis of the theoretical premises of the model mentioned above, we developed a computerized single-pool kinetic model which makes it possible to calculate the ionized dialysate sodium activity (NaDI) required to reach a pre-established target of end-dialysis blood sodium activity (NaBI). Thirty-seven non-diabetic and anuric patients undergoing regular thrice-weekly hemodialysis were given their usual dialysis treatment, with NaDI at the usual value for each patient (range 137-147 mEq/l) and kept constant throughout dialysis. At the beginning and end of the session, NaDI and NaBI were measured in quadruplicate by means of a Nova-1 device (Direct Potentiometry, Pabisch Instruments). The validity of this kinetic model was tested by considering the difference between predicted and observed (P-O) NaBI at the end of dialysis [(t)]. P-O NaBI(t) was -0.37 +/- 0.42 mEq/l, which was statistically different from 0 (p < 0.001). When P-O NaBI(t) was plotted against ONaBI(t), it was more negative at the higher values of ONaBI(t). P-O intradialytic sodium removal (Nag) was -12.5 +/- 17.8 mEq/session, which was also statistically different from 0 (p < 0.001). The imprecision of this kinetic model was less than 0.84 mEq/l, as estimated by doubling the SD of P-O NaBI(t) (0.42 = 0.84 mEq/l). Although the reasons for its inaccuracy especially at higher ONaBI(t) values remain to be clarified, these data are the expression of a satisfactory clinical model.

Molecular Epidemiology of Hepatitis C Virus Infection in Dialysis Patients

There are very few data on the molecular biology of hepatitis C virus (HCV) infection in dialysis patients. 101 patients undergoing dialysis treatment in 4 units in the Lombardy, northern Italy, were analyzed by RT-PCR for HCV viremia, by line probe assay technology for HCV genotyping and by a serological analysis for detecting type-specific antibodies. 61 of 101 (60%) patients showed detectable HCV RNA in serum; HCV genotype 2a was dominant (30/53 = 57%), followed by HCV genotype 1b (20/53 = 37%). There was no relationship between HCV genotyping and the clinical or demographic features of the patients. The antibody response toward the c33-c, c100-3, and 5-1-1 antigens was more frequent in HCV genotype 1b compared with genotype 2a (p = 0.046, p = 0.001 and p = 0.0001, respectively). The antibody levels to NS-3 and NS-4 HCV proteins were significantly higher in patients with-HCV genotype 1b in comparison with HCV 2a-infected individuals (p = 0.0001). There was a high level (82%) of agreement between HCV genotyping by RT-PCR and the assessment of type-specific antibodies by serological analysis; further, it was possible to detect type-specific antibodies in 6 of 22 (27%) patients in whom PCR amplification was unsuccessful. In conclusion, HCV subtype 2a was dominant in our population of HCV-infected dialysis patients, dialysis patients infected by different genotypes showed similar demographic and clinical characteristics, the antibody response toward the NS-3- and NS-4-related antigen of HCV was genotype dependent. There was a high level of agreement between HCV genotyping by RT-PCR and the detection of type-specific antibodies by serological analysis. As significant biological differences may exist among HCV strains, the assessment of HCV types may be very useful in the routine clinical activity of nephrologists in dialysis units.

Human serum albumin cysteinylation is increased in end stage renal disease patients and reduced by hemodialysis: mass spectrometry studies.

Abstract The aim of the present work was to monitor the covalent modifications of human serum albumin (HSA) in end stage renal diseases (ESRD) non-diabetic patients, before and after hemodialysis (HD), by direct infusion electrospray mass spectrometry (ESI-MS). Human serum samples were collected from healthy subjects (n = 10, 20–60 yr) and age-matched ESRD patients (n = 8) before and after HD, purified by affinity chromatography and analyzed by a triple-quadrupole mass spectrometer. The deconvoluted spectra from healthy subjects were all characterized by three peaks attributed to non-glycated mercaptoalbumin (HSA-SH) and to the corresponding adducts with cysteine (HSA-Cys) and glucose (HSA-Glc); relative contents: mercaptoalbumin in both glycated and non-glycated form, HSA-SHt (74 ± 6%), HSA-Cys (26 ± 5%) and HSA-Glc (24 ± 3%). HSA isolated from ESRD patients before HD was characterized by a significant reduction of HSA-SHt (42 ± 7%), and by a concomitant increase of the HSA-Cys adduct (58 ± 7%). Hemodialysis significantly reduced the cysteinylated form (37 ± 7%) and restored HSA-SHt (63 ± 8%) in all the ESRD patients. The mechanism of thiol oxidation and cysteinylation was then studied by mass spectrometry, using LQQCPF as a model peptide and H2O2 as an oxidizing agent.

Effectiveness of sodium and conductivity kinetic models in predicting end-dialysis plasma water sodium concentration: preliminary results of a single-center experience.

The attainment of a neutral sodium balance represents a major objective in hemodialysis patients. It requires that at the end of each dialysis session, total body water volume (Vf) and total plasma water sodium concentration (Napwf) are constant. Whereas to achieve a constant Vf it is sufficient that ultrafiltration equals the interdialytic increase in body weight, it is impossible to predict the value of Napwf and calculate the dialysate sodium concentration needed to obtain it without making use of kinetic mathematical models. The effectiveness of both sodium and conductivity kinetic models in predicting Napwf has already been validated in previous clinical studies. However, applying the sodium kinetic model appears to be poorly feasible in the everyday clinical practice, due to the need for blood samples at the start of each dialysis session for the determination of predialysis plasma water sodium concentration. The conductivity kinetic model appears to be more easily applicable, because no blood samples or laboratory tests are needed to determine plasma water conductivity (Cpw) and ionic dialysance (ID), used in place of plasma water sodium concentration and sodium dialysance, respectively. We applied the 2 models in 69 chronic hemodialysis patients using the Diascan Module® for the automatic determination of Cpw and ID, and using the latter as an estimate of sodium dialysance in the sodium kinetic model. The conductivity kinetic model was shown to be more accurate and precise in predicting Napwf as compared with the sodium kinetic model. Both accuracy and imprecision of the 2 models were not significantly affected by the method used to estimate total body water volume. These findings confirm the conductivity kinetic model as being an effective and easily applicable instrument for the achievement of a neutral sodium balance in chronic hemodialysis patients.

Conductivity: On-Line Monitoring of Dialysis Adequacy

Cardiovascular disease and the inadequacy of delivered dialysis are the main factors determining morbidity and mortality in dialysis patients. We have already demonstrated that a conductivity kinetic model makes it possible to match interdialytic sodium loading and intradialytic sodium removal (the main factor determining cardiovascular morbidity) without the need for blood samples and, thus, in routine clinical practice. The aim of the present study was to test the possibility of using the conductivity method also to determine Kt/v without blood or dialysate sampling. In 18 steady-state patients, the urea distribution volume (V) was kinetically determined once using ionic dialysance (D) values instead of those of effective urea clearance. One month later, the Kt/V was determined by using the current D and T values and the predetermined V (Dt/V), then compared with the equilibrated Kt/V computed by means of the SPVV kinetic model (eqKt/V). The mean value of Dt/V was 1.18 ± 0.15; while of eqKt/V it was 1.18 ± 0.16, with a mean difference of 0.00 ± 0.07. The conductivity method therefore seems to be very promising not only for monitoring the sodium balance, but also for quantifying delivered dialysis. Since its simplicity and low-cost make it suitable for use at each dialysis session, the conductivity method could therefore lead to significant progress in dialytic practice by contributing to the elimination of the two main causes of morbidity and mortality in dialysis patients.

Calcium phosphate and magnesium balance in patients with acute illness

Calcium is an essential divalent cation involved in many biological functions, such as the structural support of the body, neuromuscular and cardiovascular functions, blood coagulation, intracellular signal transmission and enzymatic reactions. There are about 1.3 kg of calcium in a normal 70 kg adult, approximately 99% of which is present in bones and teeth, 1% in soft tissue cells and 0.1% in extracellular fluid (ECF). The normal concentration of total plasma calcium is 8.4–10.4 mg/dl. Total plasma calcium exists in two forms: a protein-bound (predominantly albumin-bound) fraction, accounting for about 40% and a non protein-bound or ultrafilterable fraction, accounting for about 60% of the total plasma calcium. About 90% of the ultrafilterable calcium is in ionized form, the only homeostatically controlled and physiologically active form of plasma calcium; the remaining 10% is chelated to various anions including bicarbonate, citrate and phosphate. Changes in plasma albumin concentration must be considered in the interpretation of total plasma calcium concentration: in general, for each 1 g/dl decrease (or increase) in plasma albumin, there is a decrease (or increase) of about 0.8–1 mg/dl in total plasma calcium. The calcium binding properties of plasma albumin are affected by blood pH. Consequently plasma levels of ionized calcium (Ca2+) may change, even if there are no alterations in total plasma concentration (and vice versa). Alkalosis increases the binding of calcium to albumin and thereby reduces plasma Ca2+ concentrations, whereas the Ca2+ concentration increases in the presence of acidosis. The changes in Ca2+ levels induced by pH are usually small [1], but their clinical implications are considerable.

Comparison of second-generation screening and confirmatory assays with recombinant antigens and synthetic peptides against antibodies to hepatitis C virus : a study in renal patients

The aim of this study was to compare some common tests which are nowadays routinely used to screen and to confirm anti-HCV antibodies in renal patients. There was agreement between Ortho 2 and Abbott 2 in 94% of samples; structural and nonstructural beads of the Abbott supplementary assay were in agreement with 4-RIBA in 98 and in 85% of samples, respectively; 61% of Ortho 2 samples and 65% of Abbott 2 samples were confirmed by 4-RIBA; there was a correlation between semiquantitative analysis of screening tests (Ortho 2 and Abbott 2) and positive results by 4-RIBA; 36 and 33% of Ortho-2- and Abbott-2-positive samples were 4-RIBA indeterminate: in these instances more sophisticated techniques (polymerase chain reaction) (PCR) could be useful as a third-level assay. The comparison between Ortho 2, based on recombinant antigens, and Innotest, based on synthetic peptides, showed agreement only in 44% of samples, but this preliminary comparison cannot afford definitive conclusions. These findings suggest that second-generation assays may sometimes yield conflicting results in renal patients. These contradictions will be resolved by new HCV tests or PCR.

Fluid and electrolyte balance during extracorporeal therapies

The aims of depurative therapies in renal insufficiency are to obtain an efficient removal of metabolic waste products, and to restore and maintain body fluid, electrolyte, and acid-base homeostasis. These results may be achieved by means of the controlled transfer of solutes and water through a porous membrane placed between the patient’s blood and a properly designed solution. The membranes used for extracorporeal depurative therapies are made with a wide variety of polymeric materials, and are conventionally divided into two basic categories: those derived from the natural polymer cellulose, and those that can only be obtained by means of chemical synthesis. Both of these types of membrane are semi-permeable insofar as they allow the passage of small, but not large molecules. The permeability of dialysis membranes depends on a number of factors, including their porosity (the size and distribution of the pores), their structure and thickness, their hydrophilicity and their surface electrical charge. In the dialyzer (the device in which the semi-permeable membranes are contained), the membrane separates flowing blood (i.e. the blood compartment) from the dialysate stream (i.e. the dialysate compartment), and allows the removal of excess body water by means of ultrafiltration and the transfer of solutes from the blood to the dialysate and vice versa. The other basic elements necessary for extracorporeal depurative therapy are a vascular access, which provides the dialyzer with a large blood flow, and the dialysis machine, which prepares the dialysis solution on line, regulates blood and dialysate flows and pressures, ensures safe therapy monitoring against blood leakage and air embolism, and controls the temperature and composition of the dialysate.

Hemodialysis fluid composition

This is very important, since on the composition depends the amount of dialytic exchange of electrolytes between blood and dialysate, and thus the possibility to restore adequate body electrolytic concentrations and acid—base equilibrium. Moreover, dialysate composition is a factor strongly affecting cardiovascular stability during treatment. Thus, the choice of dialysate composition is an essential element of dialysis prescription, as well as dialyzer membrane, blood and dialysate flow rates and treatment time.