[From sodium to dialysis quantification]. / Du sodium à la quantification de la dialyse.

Sodium measurements are usually substituted by conductivity measurements in hemodialysis monitors. Ionic dialysance can be calculated from conductivity measurements and used for quantification of dialysis dose (Kt). Quantification of dialysis efficiency is based on the concept of clearance. The clearance of a solute is the blood volume fully depurated per unit time. The dialysance of a solute is the blood volume fully equilibrated with the dialysate entered into the dialyzer per unit time. For a solute absent from the diatysate delivered to the dialyzer, dia[ysance is equal to clearance. Because ions of quantitative importance (largely sodium) and urea have similar transfer characteristics through the dialyzer membrane, it can be expected that ionic dialysance is equal to urea dialysance and thus to urea clearance. Actually several studies have shown that ionic dialysance is a very good estimation of urea clearance. In comparison with the measurement of urea clearance, the measurement of ionic dialysance can be performed on-line, repeatedly and fully automatically, and is totally in expensive.

Do dialysate conductivity measurements provide conductivity clearance or ionic dialysance?

Dialysate conductivity measurements allow on-line estimation of urea clearance during hemodialysis session. Conductivity measurements provide a value of 'conductivity clearance' for some authors, but a value of 'ionic dialysance' for others. This paper aims at explaining which term should be the more appropriate. Clearance is a parameter defined for measuring the power of a mechanism, which aims at 'clearing' a solution by depurating some solutes. In hemodialysis, clearance measures the efficacy of patient's depuration. In contrast, dialysance measures the capability of transferring solutes between blood and dialysate. The conventional definition of dialysance, requiring the absence of convective transfer, should be generalized to the case of the usual presence of ultrafiltration during the hemodialysis session. For a solute (as urea) absent from the dialysate delivered to the dialyzer inlet, the clearance is equal to its dialysance. In order to avoid a dramatic fall in ionic concentrations during hemodialysis treatment, the clearance of ions is reduced by adding these ions in the dialysate and becomes lower than their dialysance. Conductivity measurements provide a value of electrolytes dialysance. Thus the term of 'ionic dialysance' is more appropriate than the term of 'conductivity clearance'. Nevertheless ionic dialysance represents a good estimation of urea clearance.

Analysis of the optical concentration curve to detect access recirculation.

The optical blood volume curve sometimes presents either a positive or a negative rapid and reversible variation (spike) during the step of the dialysate conductivity, automatically set by the monitor for the ionic dialysance (ID) measurement. We studied whether this feature was in relation with access recirculation. Firstly, we studied if the manoeuvre of reversed position of the blood lines created the same feature in the blood volume curve. Secondly, two medical teams systematically checked for the presence of spikes and measured the access recirculation by way of an ultrasound dilution technique. The manoeuvre of reversed position of the blood lines invariably reproduced the same feature on the curve of the optical blood volume measurement in case of a recirculation greater than 20%. In the normal position of the blood lines, the 16 patients with an access recirculation greater than 20% had spikes. Spikes during ID measurement were not constant for an access recirculation between 10 and 20% and did not occur for an access recirculation of less than 10% or an undetectable one. The special spike of the optical blood volume curve occurring during the ID measurement clearly detects access recirculation. The specificity is of 100% when this modification is present all along the dialysis session for all the ID measurements and the sensitivity is 100% when the access recirculation is greater than 20%.

Cardiac surgery in patients receiving long term hemodialysis. Short and long term results.

AIM: Cardiac surgery carries a high risk in hemodialysis patients and has been questioned for its results; the purpose of this study is to focus on the short and long term results in our institution. METHODS: We retrospectively analyzed the data from 124 hemodialysis patients who underwent cardiac surgery in our unit between January 1980 and December 1998; 14.5% were diabetic; 46% had isolated coronary artery disease (group 1); 29.8% had valvular disease alone (group 2); 14.5% valve and coronary disease (group 3) and 9.6% miscellaneous disease at highest risk (group 4). We analyzed the relationship between several variables (age, sex, hypertension, diabetes, previous myocardial infarction, type of disease, preoperative ejection fraction) and operative mortality (30 days) and late survival. RESULTS: The overall operative mortality was 16.9%. The only risk factor was the type of cardiac disease: operative mortality was higher in groups 3 and 4 combined than in groups 1 and 2 combined (30% versus 12.7%, p=0.07). Ninety-nine patients were followed until January 2002. Late survival rate was 46.6+/-5% at 6 years for all patients, it was significantly better in groups 1 and 2 combined than in groups 3 and 4 combined. The only risk factor for late mortality was arterial hypertension. Fifty-seven patients are still alive, 46 in groups 1 and 2, 11 in groups 3 and 4. Progression of coronary lesions occurred in 6 patients and valvular lesions in 3 patients. The remainder are doing well. CONCLUSION: Cardiac surgery seems to be justified by the severity of the lesions. Its actual results can perhaps, be improved by earlier detection of cardiac disease and better prevention of myocardial hypertrophy and cardiac calcifications.

[Ionic dialysance and quality control in hemodialysis]. / Dialysance ionique et contrôle de qualité de l'épuration en hémodialyse.

Quantification of dialysis is based on the measurement of effective urea clearance (K), dialysis dose (Kt) or normalized dialysis dose (Kt/V). During the last 20 years, Kt/V was the single parameter actually useful for quantifying dialysis efficiency, because it can be calculated from just blood or dialysate urea concentrations at the beginning and at the end of the dialysis session. However the calculation of the normalized dialysis dose (Kt/V) actually delivered to the patient cannot be performed during each dialysis session, because of the need of urea concentration measurements. Ionic dialysance is a new parameter easily measured on-line, non-invasively, automatically and without any cost during each dialysis session by a conductivity method. Because ionic dialysance has been proved equal to the effective urea clearance taking into account cardiopulmonary and access recirculation, it is becoming an actual quality-assurance parameter of the dialysis efficiency.

Hemolytic and uremic syndrome after heart transplantation.

Two cases of hemolytic and uremic syndrome in heart transplant recipients are reported. Among solid organ transplantations, this complication mainly occurred in renal transplantation and only 1 case was reported in heart transplantation in the literature. Cyclosporine was the only etiologic factor found. The renal outcome was severe with end-stage renal failure and no recovery of the renal function despite stopping cyclosporine, corticoids and plasma exchange.

Determination of access blood flow from ionic dialysance: theory and validation.

BACKGROUND: Several noninvasive techniques have been recently developed for calculating blood flow rate of vascular access in hemodialyzed patients from the on-line measurement of recirculation ratio by injecting a saline bolus when the blood lines are reversed. Here we describe a new noninvasive method based on ionic dialysance measurements without the need of a saline bolus. METHODS: Mathematical modeling allows to calculate blood flow in vascular access (QA) from the recirculation ratio (Rrev) measured when the blood lines are reversed, without the need to stop ultrafiltration, by using the formula: QA = (QB - QF) 1 - Rrev/Rrev where QB is the blood flow at the dialyzer inlet and QF the ultrafiltration rate. Because the ionic dialysance takes recirculation into account, we tested a new method to assess QA from the measurement of ionic dialysance at normal (D) and reverse (Drev) positions of the blood lines for the same QB. Assuming the absence of access recirculation at normal position of the blood lines, mathematical modeling provides the following relationship: QA = (D - QF)Drev/D - Drev. The estimation of QA from measurement of ionic dialysance (QA-ID) was compared in 28 patients to the estimation of QA by ultrasound dilution technique (QA-US). RESULTS: The two methods were strongly correlated (QA-ID = 1.24 * QA-US, r2 = 0.86, P < 0.0001). The difference between QA-ID and QA-US was 107 +/- 387 ml/min (mean +/- SD). CONCLUSIONS: Our method provides a valuable estimation of the vascular access flow and is fully noninvasive, easy to perform (no need of bolus injection and of accurate measurement of QB) and totally inexpensive. Consequently this method is suitable for monitoring access blood flow in hemodialyzed patients in order to predict access thrombosis and to treat significant stenotic lesions before thrombosis.

Festschrift for Professor Claude Jacobs. Recent developments in conductivity monitoring of haemodialysis session.

On-line monitoring of dialysate conductivity is now a standard equipment (called 'Diascan') of the dialysis monitor Integra (Hospal, Italy). From the record of the dialysate conductivity at the dialyser inlet and outlet, the Diascan calculates the values of patient's plasma conductivity and of ionic dialysance which is a weighed average of the dialysances of all ions of quantitative importance in plasma and dialysate. Because there is an equivalence between the transfer characteristics of urea and electrolytes, the ionic dialysance reflects the urea clearance corrected for recirculation. Because the conductivity of a solution is related to the concentrations of the ions and thus to the effective osmolality, the plasma conductivity is a reflection of the plasma sodium concentration. The determination of ionic dialysance and plasma conductivity by the Diascan module is fully automatic and totally inexpensive, does not require any blood or dialysate sampling and therefore can be repeated every 15 or 30 min during each dialysis session. Some clinical applications of conductivity modelling are presented: (i) the repeated measurement of ionic dialysance allows the quantification of the dialysis dose actually delivered to the patient from the beginning of the session; (ii) the measurement of ionic dialysance with blood lines in normal and reversed positions permits the easy estimation of the blood flow rate in the vascular access of the haemodialysed patient; (iii) the on-line monitoring of ionic dialysance allows the development of new methods of haemodialysis with simultaneous infusion of ions; (iv) the on-line monitoring of ionic dialysance and patient's plasma conductivity facilitates the automatic optimization of the dialysate conductivity for each individual patient.

Sodium management in dialysis by conductivity.

The determination of dialysate sodium concentration is one of the challenges of dialysis prescription, because no accurate information on the predialytic sodium overload is available. Too low dialysate sodium is responsible for intradialytic intolerance symptoms, whereas too high sodium may lead to long-term water sodium overload with cardiovascular hazards (hypertension, left heart failure). We propose here a biofeedback system based on noninvasive repeated measures of ionic dialysance and plasma water conductivity used here as a surrogate of plasma water sodium. This system achieves a stable postdialytic sodium pool and subsequently a dialysate sodium concentration adapted to the inter dialytic sodium load. This new tool in dialysate sodium prescription aims at reducing the morbidity related to patient sodium balance impairment.

Duocart biofiltration: a new method of hemodialysis.

DuoCart biofiltration (DCB) is a new hemodialysis method using a dialysate with only sodium chloride and bicarbonate obtained from two separate powder cartridges (BiCart and SelectCart, Gambro, Sweden). The ionic complement is directly reinfused in postdilution mode, using one 2 L bag of a specially designed sterile solution. The adaptation of the quantity of these infused substances to their removal through the dialysis membrane is made possible by repeated measurements of ionic dialysance (D), which are automatically performed every 30 min by the Diascan module, systematically available on the Integra dialysis monitor (Hospal, Italy), and by subsequent modification of the infusion rate (Q(R)). An appropriate kinetic model was used to determine the composition of the reinfusion solution (mM: 57 K, 47 Ca, 14.5 Mg, 180 Cl), the conductivity dialysate (set at 14.8 mS/cm) and the ratio Q(R)/D (set at 1/28). This ratio is kept constant by updating Q(R) after each measurement of D. The implementation of this technique requires an Integra dialysis monitor equipped with a two-powder-cartridge dialysate generation system. Fifteen dialysis sessions were performed (duration: 213+/-38 min; blood flow: 238+/-26 ml/min; ultrafiltration rate: 16+/-6 ml/min). The per-dialytic changes of ion plasma concentrations were monitored and found to be within the predicted range. The results substantiate the feasibility of this new hemodialysis method that presents several advantages: dialysate concentrates are in powder form, an alkaline and acetate-free dialysate is used with superior dialysate biocompatibility, no precipitation of Ca and Mg carbonate occurs in the dialysate circuit, the supply of calcium and potassium is easily adapted to individual patients' needs by change in the composition of the reinfusion solution, and a calcium-free dialysate that facilitates citrate anticoagulation is used.

Estimation of mass transfer through a hemodialyzer: theoretical approach and clinical applications.

The estimation of the solute mass transfer through a dialyzer is generally based on the solute dialysance, but the concept of dialysance has been precisely defined only in the case of a merely diffusive transfer. In actuality the mass transfer of a solute is also influenced by the ultrafiltration responsible for a convective transfer and, if the solute is an ionic substance, by the transmembrane gradient of electrical potential due to the Gibbs-Donnan effect. The aim of this paper is to generalize the concept of dialysance when the diffusive, convective, and electric components of the transfer are simultaneously active. There are at least 3 modes to generalize the concept of dialysance for it to be identical, when the amount of ultrafiltration and the Gibbs-Donnan effect are negligible, to the usual dialysance defined in the case of a merely diffusive transfer. The dialysance can be defined so that it can be equal to the clearance for a solute absent from the dialysate again, so that it still represents the rate at which the plasma concentration of a given solute is reaching its equilibrium value, or so that it represents the merely diffusive component (independent of the ultrafiltration rate) of the mass transfer. This generalized concept of dialysance can be useful to provide a real-time estimation of the effective dialysis dose actually delivered to the patient; to automatically optimize, by a biofeedback process, the sodium balance during a hemodialysis session; and to adapt dialysate concentrations for new hemodialysis techniques with convective transfer (acetate-free biofiltration).

Is ionic dialysance a valid parameter for quantification of dialysis efficiency?

The on-line measurement during hemodialysis of ionic dialysance provides an estimation of urea clearance with a good and already proven correlation. Some discrepancies remain controversial, and the influence of the dialyzer membrane is still being debated. Eighty-eight measurements of ionic dialysance (ID) were performed with a Diascan module (Hospal R&D, Int., Lyon, France), 51 with cellulosic membranes, and 37 with synthetic membranes, chosen according to their surface charges. The ID was compared to the urea clearance (UK) measured from the blood (n=16) and dialysate (n=88) sides. The ID is closely correlated (r=0.91) but significantly (p < 0.01) lower than the UK by 5% (ID/UK=0.95+/-0.06). The correlation is improved by a semilogarithmic regression analysis (r=0.93). Regarding the influence of the membrane charge, a slight difference is only evidenced for UK < 180 ml/min whereby ID is closer to the urea clearance for the charged membranes (ID/UK=0.98+/-0.05 for charged membranes versus 0.95+/-0.05 for noncharged membranes, p < 0.05). The discrepancy between ID and UK could be related with the difference in the blood distribution volume of urea and that of electrolytes. The good correlation provides the major argument for ID being used as a monitoring parameter of the delivered dialysis dose. Having integrated the discrepancy between ID and UK, prescription can be guided by ID for delivering the adequate normalized dialysis dose as defined by Kt/V.

Non-invasive monitoring of effective dialysis dose delivered to the haemodialysis patient.

Assessment of normalized dialysis dose Kt/V actually delivered to the patient carries the drawback of requiring several blood or dialysate samplings and urea concentration measurements. In order to easily quantify Kt/V, we validate here the routine implementation of an original technique for the non-invasive, on-line, and fully automatic estimation of total mean urea clearance. This estimation is obtained from the measurement by a conductivity method of the effective ionic dialysance DR, which is the dialysance of electrolytes taking into account ultrafiltration and recirculation. The observed increase in DR with ultrafiltration rate and decrease in DR with elevation of access recirculation ratio show that the estimation of DR is affected by ultrafiltration and recirculation in a consistent manner. The mean value Keff of ionic dialysance DR was compared with the value Kdc of effective urea clearance obtained by dialysate collection during 12 haemodialysis sessions. The similarity (magnitude of variation 5%) between the ionic dialysance Keff and the effective urea clearance Kdc supports the validity of the equivalence between the transfer characteristics of electrolytes and urea through the dialyser membrane. Given an estimate of the urea distribution volume V, this estimation of effective urea clearance by ionic dialysance measurement allows an on-line estimation of the normalized dialysis dose Kt/V actually delivered to the patient.

[The pitfalls of the clearance concept in hemodialysis]. / Les pièges du concept de clairance en hémodialyse.

The "clearance concept" is rigorously defined by the physicists and bioengineers. However its extension in clinical routine of dialysis therapy is not easy, but essential also to understand the rationale on which is based the currently widely used Kt/V index. The purpose of this paper is to describe the difficulties and pitfalls encountered in measuring the clearance of a substance either provided by a dialyzer or observed in a dialyzed patient. Ambiguities in the definition of clearance may account for sometimes moot estimations of the Kt/V index.