Rethinking an effective AV fistula-graft screening program. An "A B C".

The goal of a vascular access screening program is to detect and preemptively correct hemodynamically significant stenosis, however, a practice pattern allowing to implement such a program still remains to be defined. Achieving balance between the increase in access-related procedures by adopting an aggressive screening program, and the risks associated with the absence of any screening program, i.e., failure or abandonment of the arterio-venous access with need for central venous catheter placement, can be extremely challenging. All major guidelines agree about the role of arterio-venous access monitoring, but the way surveillance should be managed is still a controversial issue. Preserving long-term vascular access function should be a goal for all hemodialysis teams, yet it ideally requires a multidisciplinary effort with a monitoring program, calling for a great deal of involvement by hemodialysis health professionals. In this context, the engagement of skilled nurses and the role of patient empowerment with collaborative decision-making may be the key to a successful vascular access screening program. Screening programs should be personalized, shared with the patients, and tailored according to vascular access type and site. In the near future, new devices and the use of artificial intelligence may allow to support interpretation of complex data and lead to the development of prediction models for vascular access failure.

How to manage catheter-related right atrial thrombosis: Our conservative approach.

BACKGROUND: Catheter-related right atrial thrombosis is an underestimated, severe, and life-threatening complication of any type of central venous catheters. No clear-cut epidemiological data are available. Catheter-related right atrial thrombosis is often asymptomatic; however, it can lead to serious complications and death. CASE SERIES: We report seven catheter-related right atrial thrombosis events occurred in five hemodialysis patients; two recurrences following primary treatment are included in the report, all of them managed with a conservative approach without catheter removal. Systemic anticoagulation (vitamin K antagonists), having a well-defined target of International Normalized Ratio of 2.5-3.0, combined with urokinase as a locking solution at the end of each hemodialysis session were the therapeutic strategy used in all patients. After the first month, the anticoagulation target was reduced to an International Normalized Ratio value of 1.5-2.0 and urokinase to a weekly administration. After sixth months, when no thrombus was identified at transthoracic echocardiographic examinations, the treatment was stopped. No bleeding complications were reported. CONCLUSION: The combination therapy here described is safe, quick, and effective, achieving the goal of not removing catheters.

[Membranoproliferative glomerulonephritis with relapsing episodes of acute kidney injury in the Schnitzler syndrome].

The Schnitzler syndrome (SS) is a rare and underdiagnosed entity that associates a chronic urticarial rash, monoclonal IgM (or sometimes IgG) gammopathy and signs and symptoms of systemic inflammation. During the past 45 years the SS has evolved from an elusive, little-known disorder to the paradigm of a late-onset auto-inflammatory acquired syndrome. Though there is no definite proof of its precise pathogenesis, it should be considered as an acquired disease involving abnormal stimulation of the innate immune system, which can be reversed by the interleukin 1 (IL-1) receptor antagonist anakinra. Here we describe the case of a 56-year-old male Caucasian patient affected by SS and hospitalized several times in our unit because of relapsing episodes of acute kidney injury. He underwent an ultrasound-guided percutaneous kidney biopsy in September 2012, which showed the histologic picture of type I membranoproliferative glomerulonephritis. He has undergone conventional therapies, including nonsteroidal anti-inflammatory drugs, steroids and immunosuppressive drugs; more recently, the IL-1 receptor antagonist anakinra has been prescribed, with striking clinical improvement. Although the literature regarding kidney involvement in the SS is lacking, it can however be so severe, as in the case reported here, to lead us to recommend the systematic search of nephropathy markers in the SS.

Is the removal of a central venous catheter always necessary in the context of catheter-related right atrial thrombosis?

Catheter-related right atrial thrombosis is a severe and life-threatening complication of central venous catheters in both adult and young patients. Catheter-related right atrial thrombosis can occur with any type of central venous catheters, utilized either for hemodialysis or infusion. Up to 30% of patients with central venous catheter are estimated to be affected by catheter-related right atrial thrombosis; however, neither precise epidemiological data nor guidelines regarding medical or surgical treatment are available. This complication seems to be closely associated with positioning of the catheter tip in the atrium, whereas it is unlikely with a tip located within superior vena cava. Herein, we report the case of a patient affected by catheter-related right atrial thrombosis, who showed a quick resolution of thrombosis with a new therapeutic scheme combining loco-regional thrombolytic therapy (urokinase as a locking solution) and systemic anticoagulation therapy (vitamin K antagonists), thus avoiding catheter removal. Neither complications of the combination therapy were reported, nor recurrence of catheter-related right atrial thrombosis occurred. In conclusion, the combination therapy here described was safe, quick and effective, achieving the goal of not removing the catheter.

Kidney involvement in the Schnitzler syndrome, a rare disease.

The Schnitzler syndrome (SS) is a rare and underdiagnosed entity that associates a chronic urticarial rash, monoclonal IgM (or sometimes IgG) gammopathy and signs and symptoms of systemic inflammation. During the past 45 years, the SS has evolved from an elusive little-known disorder to the paradigm of a late-onset acquired auto-inflammatory syndrome. Though there is no definite proof of its precise pathogenesis, it should be considered as an acquired disease involving abnormal stimulation of the innate immune system, which can be reversed by the interleukin-1 receptor antagonist anakinra. It clearly expands our view of this group of rare genetic diseases and makes the concept of auto-inflammation relevant in polygenic acquired diseases as well. Increasing numbers of dermatologists, rheumatologists, allergologists, haematologists and, more recently, nephrologists, recognize the SS. The aim of this review is to focus on kidney involvement in the SS. Although the literature regarding kidney involvement in the SS is very poor it can be severe, as in our own case here reported, leading us to recommend the systematic search for nephropathy markers in the SS.

The impact of haemodialysis arteriovenous fistula on haemodynamic parameters of the cardiovascular system.

BACKGROUND: Satisfactory vascular access flow (Qa) of an arteriovenous fistula (AVF) is necessary for haemodialysis (HD) adequacy. The aim of the present study was to further our understanding of haemodynamic modifications of the cardiovascular system of HD patients associated with an AVF. The main objective was to calculate using real data in what way an AVF influences the load of the left ventricle (LLV). METHODS: All HD patients treated in our dialysis unit and bearing an AVF were enrolled into the present observational cross-sectional study. Fifty-six patients bore a lower arm AVF and 30 an upper arm AVF. Qa and cardiac output (CO) were measured by means of the ultrasound dilution Transonic Hemodialysis Monitor HD02. Mean arterial pressure (MAP) was calculated; total peripheral vascular resistance (TPVR) was calculated as MAP/CO; resistance of AVF (AR) and systemic vascular resistance (SVR) are connected in parallel and were respectively calculated as AR = MAP/Qa and SVR = MAP/(CO - Qa). LLV was calculated on the principle of a simple physical model: LLV (watt) = TPVR·CO(2). The latter was computationally divided into the part spent to run Qa through the AVF (LLVAVF) and that part ensuring the flow (CO - Qa) through the vascular system. The data from the 86 AVFs were analysed by categorizing them into lower and upper arm AVFs. RESULTS: Mean Qa, CO, MAP, TPVR, LLV and LLVAVF of the 86 AVFs were, respectively, 1.3 (0.6 SD) L/min, 6.3 (1.3) L/min, 92.7 (13.9) mmHg, 14.9 (3.9) mmHg·min/L, 1.3 (0.6) watt and 19.7 (3.1)% of LLV. A statistically significant increase of Qa, CO, LLV and LLVAVF and a statistically significant decrease of TPVR, AR and SVR of upper arm AVFs compared with lower arm AVFs was shown. A third-order polynomial regression model best fitted the relationship between Qa and LLV for the entire cohort (R (2) = 0.546; P < 0.0001) and for both lower (R (2) = 0.181; P < 0.01) and upper arm AVFs (R (2) = 0.663; P < 0.0001). LLVAVF calculated as % of LLV rose with increasing Qa according to a quadratic polynomial regression model, but only in lower arm AVFs. On the contrary, no statistically significant relationship was found between the two parameters in upper arm AVFs, even if mean LLVAVF was statistically significantly higher in upper arm AVFs (P < 0.0001). CONCLUSIONS: Our observational cross-sectional study describes statistically significant haemodynamic modifications of the CV system associated to an AVF. Moreover, a quadratic polynomial regression model best fits the relationship between LLVAVF and Qa, but only in lower arm AVFs.

Efficacy and Safety of a New Technique of Conversion from Temporary to Tunneled Central Venous Catheters.

The usually applied conversion technique from temporary to tunneled central venous catheters (CVCs) using the same venous insertion site requires a peel-away sheath. We propose a conversion technique without peel-away sheath: a guide wire is advanced through the existing temporary CVC; then, a subcutaneous tunnel is created from the exit to the venotomy site. After removing the temporary CVC, the tunneled one is advanced along the guide wire. The study group included all patients requiring a catheter conversion from January 2012 to June 2014; the control group included incident patients who had received de novo placement of tunneled CVCs from January 2010 to December 2011. The main outcome measures were technical success and immediate complications. Seventy-two tunneled catheters (40 with our conversion technique and 32 with the traditional one) were placed in 72 patients. The technical success was 95% in the study group and 75% in the controls (p = 0.019). The immediate complications were one bleeding in the study group (2.5%) and one air embolism, one pneumothorax, and four bleedings (18.7%) in the controls (p = 0.039). Conversion from temporary to tunneled CVC using a guide wire and without a peel-away sheath is an effective and safe procedure.

Ranking of factors determining potassium mass balance in bicarbonate haemodialysis.

BACKGROUND: One of the most important pathogenetic factors involved in the onset of intradialysis arrhytmias is the alteration in electrolyte concentration, particularly potassium (K(+)). METHODS: Two studies were performed: Study A was designed to investigate above all the isolated effect of the factor time t on intradialysis K(+) mass balance (K(+)MB): 11 stable prevalent Caucasian anuric patients underwent one standard (∼4 h) and one long-hour (∼8 h) bicarbonate haemodialysis (HD) session. The latter were pair-matched as far as the dialysate and blood volume processed (90 L) and volume of ultrafiltration are concerned. Study B was designed to identify and rank the other factors determining intradialysis K(+)MB: 63 stable prevalent Caucasian anuric patients underwent one 4-h standard bicarbonate HD session. Dialysate K(+) concentration was 2.0 mmol/L in both studies. Blood samples were obtained from the inlet blood tubing immediately before the onset of dialysis and at t60, t120, t180 min and at end of the 4- and 8-h sessions for the measurement of plasma K(+), blood bicarbonates and blood pH. Additional blood samples were obtained at t360 min for the 8 h sessions. Direct dialysate quantification was utilized for K(+)MBs. Direct potentiometry with an ion-selective electrode was used for K(+) measurements. RESULTS: Study A: mean K(+)MBs were significantly higher in the 8-h sessions (4 h: -88.4 ± 23.2 SD mmol versus 8 h: -101.9 ± 32.2 mmol; P = 0.02). Bivariate linear regression analyses showed that only mean plasma K(+), area under the curve (AUC) of the hourly inlet dialyser diffusion concentration gradient of K(+) (hcgAUCK(+)) and AUC of blood bicarbonates and mean blood bicarbonates were significantly related to K(+)MB in both 4- and 8-h sessions. A multiple linear regression output with K(+)MB as dependent variable showed that only mean plasma K(+), hcgAUCK(+) and duration of HD sessions per se remained statistically significant. Study B: mean K(+)MBs were -86.7 ± 22.6 mmol. Bivariate linear regression analyses showed that only mean plasma K(+), hcgAUCK(+) and mean blood bicarbonates were significantly related to K(+)MB. Again, only mean plasma K(+) and hcgAUCK(+) predicted K(+)MB at the multiple linear regression analysis. CONCLUSIONS: Our studies enabled to establish the ranking of factors determining intradialysis K(+)MB: plasma K(+) → dialysate K(+) gradient is the main determinant; acid-base balance plays a much less important role. The duration of HD session per se is an independent determinant of K(+)MB.

Probing the dry weight by bioimpedance: the resistance stabilization test.

Probing dry weight (DW) was largely dependent on clinical subjective estimate until recently. New bedside non-invasive tools have been developed with the aim of providing more objective information on volume status and guiding physicians in the quest for DW. Among them, bioimpedance appears to be very promising in the achievement of this goal. We have developed a test aimed to assess DW in complicated hemodialysis (HD) patients and named it "RE.sistance S.tabilization T.est" (RE.S.T.). It is based on the following four items: 1. one or more HD sessions lasting 6 h with ultrafiltration (UF) rate ≤0.5 kg/h are planned; 2. bioimpedance measurements are determined injecting 800 µA at 50 kHz alternating sinusoidal current with a standard tetrapolar technique. Resistance (R) is recorded at the start of the treatment (R0) and every 15 min (Rt) during HD until the end of the 6-h session; 3. DW is defined as that achieved at the time point at which three consecutive R0/Rt ratios show in-between changes ±1% despite ongoing UF; 4. if at the end of the 6-h HD session R stabilization is not attained, a new 6-h HD treatment with UF rate ≤0.5 kg/h is planned until a bioimpedance DW (according to the item 3) is obtained. As said, we are applying RE.S.T. to assess DW in complicated HD patients. Here we report a paradigmatic case which illustrates quite brilliantly its clinical usefulness. The patient was admitted to our nephrology ward with a hypertensive crisis, a very large drug regimen notwithstanding. His DW was reduced by 5 kg after four 6-h HD sessions probing his DW by means of RE.S.T. He was discharged with a normal blood pressure and no need for anti-hypertensive drugs. In conclusion, RE.S.T. appears to be a (the) brilliant solution in solving the old problem of DW in HD patients.

[Rescue endovascular revascularization in two patients with bilateral atherosclerotic renal artery occlusion]. / Rivascolarizzazione endovascolare di salvataggio in due pazienti con occlusione aterosclerotica bilaterale dell'arteria renale.

Renal artery stenosis is found in 2% and 40% of general and high cardiovascular risk populations, respectively. Atherosclerotic renal artery stenosis (ARAS) has become an increasingly recognized clinical condition, especially in older or otherwise atherosclerosis-prone populations. This increase in prevalence has led to a dramatically increased use of percutaneous transluminal renal angioplasty. Randomized trials have failed to demonstrate any superiority of renal revascularization over medical therapy as far as control of hypertension, mortality or cardiovascular events is concerned. However, in this report we present two cases in which rescue endovascular revascularization in patients affected by bilateral ARAS permitted withdrawal from hemodialysis treatment and the restoration of a certain degree of renal function. In conclusion, for certain carefully-selected high-risk patients, renal revascularization may still have an important role. The two cases presented in this article are good examples of the extraordinary benefit that endovascular revascularization can bestow.

[A technique for inserting inadvertently removed tunneled hemodialysis catheters through the original exit site]. / Una tecnica per il riposizionamento del catetere venoso centrale tunnellizzato fuoriscito accidentalmente mediante infilaggio dall'exit site.

Accidental loss of tunneled hemodialysis (HD) central venous catheters (CVCs) is a rare complication. In the absence of other sites available for positioning a new CVC, the lack of a vascular access exposes the patient to a high risk of mortality. The technique for inserting inadvertently removed tunneled CVCs using the original exit site has never gained popularity and has been used, although with good results, in selected cases only. The purpose of this case report is to describe our experience in similar cases, and to propose a variant of the procedure described above: in 4 cases occurring over the last 12 months, our technique permitted recovery of vascular access for up to 72 hours after the loss of the CVC, with placement of a new cuffed CVC performed in the space of a few minutes. There were no cases of bleeding nor episodes of infection. The patients resumed their regular HD program with adequate performance of the CVC during a follow-up period that ranged from 3 to 12 months.In conclusion, we believe that this simple manoeuvre can help the nephrologist solve one of the dialysis room's moments of genuine emergency.

Sodium setpoint and gradient in bicarbonate hemodialysis.

BACKGROUND: The demonstration of an individual osmolar setpoint in hemodialysis (HD) is crucial to individualize dialysate sodium concentrations. Furthermore, the diffusive gradient between plasma and dialysate sodium is important in the "fine tuning" of the intradialytic sodium mass balance (MB). METHODS: The design of this study included part A: a retrospective analysis of predialysis plasma sodium concentrations extracted from a 6-year database in our HD population (147 prevalent white anuric patients); and part B: study of intradialytic sodium kinetics in 48 patients undergoing one 4-hour bicarbonate HD session. Direct potentiometry with an ion-selective electrode was used for sodium measurements. RESULTS: Study part A: the mean number of plasma sodium measurements per patient was 16.06 ± 14.03 over a mean follow-up of 3.55 ± 1.76 years. The mean of the averaged plasma sodium concentrations was 136.7 ± 2.1 mmol/L, with a low mean intraindividual coefficient of variation (1.39 ± 0.4). Study part B: mean predialysis and postdialysis plasma sodium concentrations were 135.8 ± 0.9 and 138.0 ± 0.9 mmol/L (p<0.001). Mean inlet dialyzer sodium concentration was 138.7 ± 1.1 mmol/L; the hourly diffusion concentration gradients showed a statistically significant transfer from dialysate to plasma (Wilks ? <0.0001). A statistically significant relationship was found between sodium MB and diffusion gradient (p<0.02), and between sodium MB and ultrafiltration volume (p<0.01). CONCLUSIONS: A relatively "fixed" and individual osmolar setpoint in HD patients was shown for the first time in a long-term follow-up. A dialysate sodium concentration of 140 mmol/L determined a dialysate to plasma sodium gradient.

Optimizing the dialysate calcium concentration in bicarbonate haemodialysis.

BACKGROUND: There is no consensus regarding the optimal dialysate calcium concentration (DCa) during haemodialysis (HD). Low DCa may predispose to acute arrhythmias, whereas high DCa increases the long-term risk of soft tissue calcifications. METHODS: Twenty-two HD patients treated in four dialysis centres underwent two HD sessions, respectively, with 1.5 and 1.25 mmol/L total DCa. Calcium mass balance (CMB) was calculated from ionized calcium (iCa) in the dialysate and blood at the start and end of each run, using a kinetic formula to define the mean concentrations in the blood and dialysate and then estimating CMBs over the entire treatments. RESULTS: Mean blood iCa levels increased using 1.5 DCa, whereas they remained unchanged using 1.25 DCa. Diffusive CMB positively correlated with the dialysate/blood iCa gradient. With 1.5 DCa, diffusive CMBs were strongly positive at the blood side and negative at the dialysate side, indicating transfer from dialysate to blood. With 1.25 DCa, despite a negative dialysate/blood iCa gradient, diffusive CMB was slightly positive in blood and negative in dialysate. The global balances based on both the convective and diffusive components showed a positive net transfer of Ca from dialysate to blood with 1.5 DCa and an approximately neutral Ca flux with 1.25 DCa. CONCLUSIONS: While CMB is nearly neutral when using 1.25 DCa, the use of 1.5 DCa results in a gain of Ca during HD. The risks associated with Ca load should be considered in the choice of DCa prescription for HD but need also be weighed against the risk of worse haemodynamic dialysis tolerance.

Effect of dialysate calcium concentrations on parathyroid hormone and calcium balance during a single dialysis session using bicarbonate hemodialysis: a crossover clinical trial.

BACKGROUND: In bicarbonate-based hemodialysis, dialysate total calcium (tCa) concentration may have effects on mineral metabolism. STUDY DESIGN: Randomized crossover trial of 3 dialysate tCa concentrations (2.5, 2.75, and 3.0 mEq/L). SETTING & PARTICIPANTS: 22 stable anuric uremic patients underwent three 4-hour bicarbonate hemodialysis sessions with the 3 different dialysate tCa concentrations using a single-pass batch dialysis system. OUTCOMES: Hourly measurements of plasma water ionized calcium (iCa) and plasma parathyroid hormone (PTH) concentrations. tCa mass balances were measured from the dialysate side. RESULTS: Hourly plasma water iCa concentrations were higher with a dialysate tCa concentration of 3.0 compared with 2.75 and 2.5 mEq/L (P < 0.05), as were iCa concentrations at the end of dialysis sessions (2.66 ± 0.1, 2.56 ± 0.12, and 2.4 ± 0.08 mEq/L, respectively; P < 0.001). Mean tCa mass balance values (diffusion gradient from the dialysate to the patient) were positive with all dialysate tCa concentrations and increased progressively with dialysate tCa concentration (75 ± 122, 182 ± 125, and 293 ± 228 mg, respectively; P < 0.001). Plasma PTH levels increased during dialysis using dialysate tCa concentration of 2.5 mEq/L (mean increase, 225 ± 312 pg/mL) and decreased with dialysate tCa concentrations of 2.75 and 3.0 mEq/L (mean decreases, 68 ± 325 and 99 ± 432 pg/mL, respectively). LIMITATIONS: Small sample size and lack of measurement of total-body calcium mass balances. CONCLUSIONS: A dialysate tCa concentration of 2.75 mEq/L might be preferable to 2.5 or 3.0 mEq/L because it is associated with mildly positive tCa mass balance values, plasma water iCa levels in the reference range, and stable PTH levels during dialysis.

The systemic capillary leak syndrome: a scarcely known nephrological entity.

The idiopathic systemic capillary leak syndrome (SCLS) is a rare life-threatening disorder characterized by periodic episodes of hypovolemic shock, due to plasma leakage from the intravascular to the interstitial space, as reflected by accompanying hypoalbuminemia, hemoconcentration and edema. Here we report the case of a 65-year-old woman affected by SCLS who required aggressive resuscitation with norepinephrine, steroids, albumin and crystalloids. Then, a long-term prophylaxis with a ß(2)-adrenergic receptor agonist and theophylline was started. In conclusion, though SCLS is a rare entity, the associated morbidity and mortality require the physician's awareness to provide timely therapy. Underrecognition in the medical community and rarity of this syndrome have precluded analysis by rational clinical trial designs that are necessary to determine more targeted and adequate therapy. This report is meant to enhance awareness of SCLS in the nephrology community.

Effects of different dialysate calcium concentrations on intradialysis hemodynamic stability.

BACKGROUND: The interplay of correct solute mass balances, such as those of sodium (Na+), potassium (K+) and total calcium (tCa) (Na+MB, K+MB and tCaMB, respectively) with adequate ultrafiltration volumes (VUF) is crucial to achieving hemodynamic stability during hemodialysis (HD). METHODS: Twenty-two stable anuric uremic patients underwent three 4-hour bicarbonate HD sessions, each with a different dialysate tCa concentration (1.25, 1.375 and 1.50 mmol/L). The GENIUS dialysis system (Fresenius Medical Care, Germany) was used. Volumes of blood and dialysate processed, VUF and dialysate Na+ and K+ concentrations were prescribed to be the same. Hourly measurements of plasma water ionized Ca (Ca++), Na+ and K+ were made, and their trends analyzed. tCaMBs, Na+MBs and K+MBs were determined. Systolic (SBP), diastolic (DBP) blood pressure, mean arterial pressure (MAP) and heart rate (HR) trends during dialysis were analyzed. RESULTS: Mean hourly plasma water Ca++ concentrations were statistically significantly higher with a dialysate tCa concentration of 1.50 mmol/L. Mean tCaMBs were positive (diffusion gradient from the dialysate to the patient), increasing with increasing dialysate tCa concentrations (+75 ± 122 mg, +182 ± 125 mg, +293 ± 228 mg, respectively). Their difference was statistically significant (p<0.0005). Mean Na+MBs and K+MBs were not statistically significantly different. SBP, DBP, MAP and HR were not statistically significantly different among the 3 treatments. CONCLUSIONS: These highly controlled experiments showed that hemodynamic stability does not appear to be statistically significantly influenced by any specific dialysate tCa concentration in this peculiar subset of patients.

Bioimpedance and the duration of the hemodialysis session.

Bioelectrical impedance analysis (BIA) is composed of resistance (R) and reactance (Xc). The aim of this study was to investigate whether BIA may be influenced by the duration of hemodialysis (HD) sessions. Eleven uremic patients underwent one 4-hour and one 8-hour bicarbonate HD session. Volume of blood and dialysate processed, volume of ultrafiltration (V(UF)), and dialysate electrolyte concentrations were prescribed to be the same. R and Xc were determined at the start and the end of each session, injecting 800 µA at 50 kHz alternating sinusoidal current (BIA 101; Akern, Italy). Mean pre- and postdialysis body weights and V(UF) were not significantly different in the 4-hour and 8-hour treatments. Postdialysis R, ΔR (the difference between post- and predialysis R values), and percent increase of R values were significantly higher in the 8-hour sessions, when compared with the corresponding values of the 4-hour sessions (p < 0.0001, 0.02, and 0.02, respectively). In conclusion, this study shows that 8-hour HD sessions were associated with postdialysis R, ΔR, and percent increase of R values significantly higher than the corresponding ones of 4-hour sessions. If higher R values may represent a proxy of a correct dry body weight, it remains a matter of future research.

Calcium mass balances during standard bicarbonate hemodialysis and long-hour slow-flow bicarbonate hemodialysis.

BACKGROUND: Dialysate calcium (Ca) concentration should be viewed as part of the integrated therapeutic regimen to control renal osteodystrophy and maintain normal mineral metabolism. Thus, a correct ionized calcium mass balance (Ca++MB) during hemodialysis (HD) is crucial in the treatment of renal osteodystrophy. The GENIUS single-pass batch dialysis system (Fresenius Medical Care, Germany) consists of a closed dialysate tank of 90 L; it offers the opportunity of effecting mass balances of any solute in a very precise way. METHODS: The present study has a crossover design: 11 stable anuric HD patients underwent 2 bicarbonate HD sessions, 1 of 4 hours (4h) and the other of 8 hours (8h) in a random sequence, always at the same interdialytic interval, at least 1 week apart. The GENIUS system and high-flux FX80 dialyzers (Fresenius Medical Care, Germany) were used. The volume of blood and dialysate processed, volume of ultrafiltration and dialysate Ca concentrations (1.50 mmol/L) were prescribed to be the same. Trends of plasma Ca++, blood pH and bicarbonates during dialysis, as well as Ca++MBs were determined. Plasma parathyroid hormone (PTH) levels at the start and end of the 2 treatments were measured. RESULTS: Ca++MBs (mean ± SD) were +284.6 ± 137.4 mg and +297.7 ± 131.6 mg (p=0.307) in the 4h and 8h treatments, respectively. No single session out of the 22 had a negative Ca++MB for the patient. Mean plasma Ca++, blood pH and bicarbonate levels were not statistically significantly different when comparing the start and end of the sessions of the 2 treatments. Mean plasma Ca++, blood pH and bicarbonate levels increased significantly along the time points in both 4h and 8h HD sessions (repeated measures ANOVA: p<0.0001). Mean plasma PTH levels were not statistically significantly different when comparing the start and end of the sessions of the 2 treatments. The differences between predialysis and postdialysis plasma PTH levels were not statistically significantly different either in 4h or 8h sessions (Wilcoxon's test: p=NS), even though a trend toward lower postdialysis plasma PTH levels was observed in both 4h and 8h treatments. CONCLUSIONS: Our data show incontrovertibly that, when dialyzing with a dialysate Ca concentration of 1.50 mmol/L, 4h standard bicarbonate HD and 8h slow-flow bicarbonate HD always achieve a quite similar positive Ca++MB for the patients.

Removal of uraemic retention solutes in standard bicarbonate haemodialysis and long-hour slow-flow bicarbonate haemodialysis.

BACKGROUND: Several studies already stressed the importance of haemodialysis (HD) time in the removal of uraemic toxins. In those studies, however, also the amount of dialysate and/or processed blood was altered. The present study aimed to investigate the isolated effect of the factor time t (by processing the same total blood and dialysate volume in two different time schedules) on the removal and kinetic behaviour of some small, middle and protein-bound molecules. METHODS: The present study had a crossover design: 11 stable anuric HD patients underwent two bicarbonate HD sessions (~ 4 and ~ 8 h) in a random sequence, at least 1 week apart. The GENIUS single-pass batch dialysis system and the high-flux FX80 dialysers (Fresenius Medical Care, Bad Homburg, Germany) were used. The volume of blood and dialysate processed, volume of ultrafiltration, and dialysate composition were prescribed to be the same. For each patient, blood was sampled from the arterial line at 0, 60, 120, 180 and 240 min (all sessions), and at 360 and 480 min (8-h sessions). Dialysate was sampled at the end of HD from the dialysate tank. The following solutes were investigated: (i) small molecules: urea, creatinine, phosphorus and uric acid; (ii) middle molecule: ß(2)M; and (iii) protein-bound molecules: homocysteine, hippuric acid, indole-3-acetic acid and indoxyl sulphate. Total solute removals (solute concentration in the spent dialysate of each analyte × 90 L - the volume of dialysate) (TSR), clearances (TSR of a solute/area under the plasma water concentration time curve of the solute) (K), total cleared volumes (K × dialysis time) (TCV), and dialyser extraction ratios (K/blood flow rate) (ER) were determined. The percent differences of TSR, K, TCV and ER between 4- and 8-h dialyses were calculated. Single-pool Kt/Vurea, and post-dialysis percent rebounds of urea, creatinine and ß(2)M were computed. RESULTS: TSR, TCV and ER were statistically significantly larger during prolonged HD for all small and middle molecules (at least, P < 0.01). Specifically, the percent increases of TSR (8 h vs 4 h) were: for urea 22.6.0% (P < 0.003), for creatinine 24.8% (P < 0.002), for phosphorus 26.6% (P < 0.001), and for ß(2)M 39.2% (P < 0.005). No statistically significant difference was observed for protein-bound solutes in any of the parameters being studied. Single-pool Kt/Vurea was 1.41 ± 0.19 for the 4-h dialysis sessions and 1.80 ± 0.29 for the 8-h ones. The difference was statistically significant (P < 0.0001). Post-dialysis percent rebounds of urea, creatinine and ß(2)M were statistically significantly greater in the 4-h dialysis sessions (at least, P < 0.0002). CONCLUSIONS: The present controlled study using a crossover design indicates that small and middle molecules are removed more adequately from the deeper compartments when performing a prolonged HD, even if blood and dialysate volumes are kept constant. Hence, factor time t is very important for these retention solutes. The kinetic behaviour of protein-bound solutes is completely different from that of small and middle molecules, mainly because of the strength of their protein binding.