José Antonio Milán

Survival and factors predicting mortality in hemodialysis patients over 75 years old

BACKGROUND Patients starting dialysis treatments are increasingly elderly and with high morbidity and mortality. Survival and factors influencing mortality are discussed. METHODS We studied 2,601 patients who started hemodialysis in Andalucía (Spain) between 2004 and 2007. Of these, 71 patients died in the first 90 days of hemodialysis treatment and were excluded. Three groups were considered: group A, 694 patients aged less than 60 years; group B, 1,203 patients between 60 and 75 years; and group C, 704 patients aged over 75. Survival and factors associated with mortality were studied. RESULTS Mean survival was 46 months in group A, 41.6 in group B and 35 in the very elderly group. In univariate analysis using the Cox proportional hazards model, survival in the very elderly patients was significantly influenced by low body mass index (BMI), venous catheter as initial vascular access, arterial hypertension, congestive heart failure (CHF), late referral to nephrologist (<6 months), C-reactive protein (CRP) >10 mg/dL, serum albumin <3.5 g/dL, Kt/V (Daugirdas) <1.2 and time of dialysis session <180 minutes. In multivariate analysis, BMI, CHF, CRP, low serum albumin, Kt/V and time of dialysis session remained as independent predictors of mortality. CONCLUSIONS Survival of the very elderly patients who remained on hemodialysis more than 90 consecutive days was poor (about 3 years). Heart failure and malnutrition/inflammation are prognostic factors related to mortality in these patients on chronic hemodialysis.

A novel mathematical method based on urea kinetic modeling for computing the dialysis dose

A novel normalized single pool urea kinetic model (nspUKM) for the quantification of the urea removal, dialyzer urea clearance and urea generation rate during a dialysis session, is presented. Its major goal is the computation of an accurate estimate of the fractional dialyzer urea clearance (dKt/V), which is denoted nKt/V, in contrast to the equilibrated Kt/V (eKt/V). This work clarifies the significance of dKt/V as a complement to eKt/V in hemodialysis (HD) prescription and quantification. This new model emerges from a generalization of the standard single pool urea kinetic model (spUKM) of the US National Cooperative Dialysis Study (NCDS), identified as gspUKM. Due to their significance, the standard single pool Kt/V (spKt/V) and the eKt/V are also analyzed from gspUKM in this work, with the aim of achieving a better interpretation of the results. Indices nKt/V, eKt/V and spKt/V have been compared with the dKt/V computed from a published and validated two-pool urea kinetic model (2pUKM). We present the results obtained from a clinical study carried out on a group of 30 end stage renal disease (ESRD) patients. The limits of agreement (mean+/-2S.D. (standard deviation) of the difference) between nKt/V and 2pKt/V were -0.077+/-0.72% (percentage of the dKt/V mean), while between eKt/V and 2pKt/V were -13.75+/-17.39% and between spKt/V and 2pKt/V were -1.61+/-6.54%. These scores prove that the nspUKM model is able to provide a very accurate estimate of 2pKt/V and thus dKt/V, even with high flux (HF) HD. The presented method joins the simplicity of single-pool models to the accuracy of double-pool models, when the target is the identification of the dialyzer urea clearance, urea removal and urea generation rate, although it does not provide a good prediction of the urea dynamics. Finally, we think that our analytical and experimental findings throw light on the behavior and applicability of the different Kt/V indices analyzed.

Renal Telehealthcare System Based on a Patient Physiological Image: A Novel Hybrid Approach in Telemedicine

This paper presents a novel renal telemedicine system, Virtual Center for Renal Support (VCRS), focused on the end-stage renal disease (ESRD) population. The VCRS design modifies the telemedicine paradigm, currently centered on communication technologies and monitoring devices, by emphasizing the way that biosignals are used to extract on-line knowledge to be used by physicians to solve current needs of this population. We begin with an ESRD review, from which a summary of major limitations of current renal health assistance programs is obtained. This is used to form the basis for the VCRS. This work is focused on a theoretical description of the technological architecture of VCRS, followed by a simulation experiment showing some preliminary results from a prototype of a patient physiologic image (PPI) computer component, the major knowledge creator of VCRS. Preliminary results show that PPI technology provides the ability to supervise internal variables representing the patients dynamic behavior. The demonstrated relation between adequate control of extracellular volume and blood pressure suggests that VCRS is able to generate hypovolemia warnings before their occurrence during a hemodyalysis session delivered remotely. However, PPI is not restricted to kinetic models, which were initially chosen because of their successful results in the provision of dialysis. Preliminary results suggest the ability of this telemedicine system to enhance remote patient supervision and care.

Applications of Bioimpedance to End Stage Renal Disease (ESRD)

This chapter develops a thorough review of the methods and techniques used for the analysis of body composition of renal patients based on bioimpedance measurements. The work ranges from the physical principles, to bioelectric models of human body, instrumentation, configurations in the position of electrodes, equations to calculate body composition, bioimpedance nephrological applications and clinical analysis of results. This text provides a multidisciplinary approach that will allow the reader to understand and comprehend this kind of technology, so it can be used both by engineers as a basis for the development of bioimpedance medical devices, and by medical staff to apply the bioimpedance analysis techniques in a better control and management of patients with ESRD.

Improving hollow fiber dialyzer efficiency with a recirculating dialysate system I : Theory and applicability

The mathematical theory that underlies a novel non-regenerated recirculating dialysate system (RDS) for improving diffusive clearance in hemodialyzers is presented. The theory states the conditions that hemodialyzers must meet to be suitable in RDS optimization. We have verified the applicability of the RDS for several Cuprophan and polysulfone (PS) commercial dialyzers, showing that PS (synthetic) membranes achieve the highest increments of diffusive clearance. A numerical simulation analysis over more general conditions defined by the dimensionless groups of the system demonstrated that the highest diffusive clearance improvements are achieved in dialyzers operating with a low value of the diffusive mass-transfer area/blood flow rate ratio. This study has provided the base for the assessment of the performance of the RDS as compared to several high-efficiency systems, presented in Part II of this work [M. Prado, L. M. Roa, A. Palma, and J. A. Milán, Ann. Biomed. Eng. (2004) submitted].

Improving Hollow Fiber Dialyzer Efficiency with a Recirculating Dialysate System II: Comparison Against Two-Chamber Dialysis Systems

The theoretical basis of the nonregenerated recirculating dialysate system (RDS) was derived in Part I of this work [M. Prado, L. M. Roa, A. Palma, and J. A. Milán, Ann. Biomed. Eng. (2005)]. This system pursues the maximization of the clearance of hollow fiber dialyzers whose performance is controlled by diffusion, as occurred in standard hemodialysis. In this second part we perform a comparison by digital simulation of the RDS against three well-known two-chamber dialysis systems. As a major outcome, the efficiency of the RDS increased by a factor of five–eight with respect to the efficiency of a single dialyzer operating with a number of transfer units equal to 0.1, that is when the diffusive mass-transfer of the dialyzer is exhausted. Present low-flux dialyzers do not take advantage of the full potential of this technique, but the functional domain where high-flux and high-area dialyzers operate could be more suitable to exploit this technique. We conclude that RDS can be a competitive efficient technique for optimizing the dialysis efficiency.

Kinetic indices and dialysis outcomes

Performance and methodology issues associated to Kt/V indices for hemodialysis adequacy are analyzed by means of concepts obtained from dynamics similarity theory, together with urea kinetic modeling. This theoretical analysis suggests the acceptance of Kt/V against other indices like Kt. Afterwards, the study justifies, presents, and validates by means of a cross-sectional study over 98 chronic renal patients, a novel mathematical-clinical procedure, which provides a good and clinically efficient estimate of dialyzer-based Kt/V (dKt/V), as a complement to equilibrated Kt/V (eKt/V).

Single Pool Urea Kinetic Modeling

Hemodialysis (HD) is one of the treatments included in what is called the Renal Replacement Therapy (RRT). As every treatment, hemodialysis has its dose. How quantify this hemodialysis dosage was one of the results of the National Dialysis Cooperative Study (NCDS) published in 1983. A formula based in the Urea Kinetic Modeling (UKM) was developed. This formula was the dimensionless equation Kt/V where K is the dialyzer clearance rate of urea (or volume of plasma cleared), t is the duration of the dialysis session and V is the urea distribution volume (the total body water volume). Because of the complexity of urea kinetic modeling, a number of shortcut methods of estimating Kt/V have been proposed. The aims of this chapter are twofold: 1) to give an overview of single pool urea kinetic modeling and 2) to introduce concepts and methods needed to manage the approaches available to estimate the single pool Kt/V.

Urea kinetic modelling: new hemodialysis prescription procedure

The National Cooperative Dialysis Study (NCDS) showed the viability of the single-pool urea kinetic model (spUKM) to maintain the blood urea nitrogen (BUN) level of the renal patient in an adequate target interval, defining the single-pool normalized clearance of urea spKt/V as an index of the hemodialysis dose. However, the urea distribution is a nonuniform problem, due to the barriers between pools in the body distribution volume. The urea rebound induced by the hemodialysis is a consequence of this nonuniform distribution and limits the applicability of the NCDS. The viability of a more recent index, the equilibrated Kt/V (eKt/V), is being studied, because it is not affected by the urea rebound. This index is defined substituting the postdialysis BUN by equilibrated BUN (measured about an hour from the end of hemodialysis). In spite of its good results to calculate the hemodialysis dose in the presence of urea rebound, the eKt/V is unable to prescribe a hemodialysis, because the equilibrated clearance is different to the dialyzer clearance. We present a new hemodialysis prescribing procedure which calculates the adequate dialyzer clearance to obtain a target time averaged concentration of urea. This procedure is supported by a new model that we have developed: the normalized single-pool urea kinetic model (spUKM/sup norm/), which is able to calculate a good approximation to the real Kt/V based in dialyzer clearance. The eKt/V and spKt/V are used in intermediate steps of our procedure, and so the actual advances in these indexes can be taken into account.

Analysis of Anomalies in Bioimpedance Models for the Estimation of Body Composition

Bioimpedance analysis is a simple, safe and noninvasive method for Body Composition Estimation (BCE), which is of great interest for the monitoring of patients on renal replacement therapy. The most featured bioimpedance devices available are based on the bioimpedance spectroscopy technique, the extended Cole model and the Hanai Mixture theory. However, a set of anomalies using these methods has been found in this paper during the study of the evolution of body composition in patients on peritoneal dialysis. The main results obtained show that the estimates resulting from bioimpedance values that differ significantly from the single-dispersion Cole model have to be taken with some caution. This issue highlights the importance of medical assessment (technical or specialist) when interpreting any bioimpedance related data.