**Measuring System of Urea in Blood by Application in Recirculation for Hemodialysis Treatment**

G.A. Martinez *Department of Nephrology Hemodialysis Subsection Military Hospital Center México D.F.* 

#### **1. Introduction**

214 Technical Problems in Patients on Hemodialysis

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End stage renal disease (ESRD) is one of the most common life-threatening diseases. The number of patients accepted for renal replacement therapy including hemodialysis (HD), peritoneal dialysis, and kidney transplantation in developed and developing countries increases each year and imposes a major social and economic burden on these communities.(1) With an increasing number of elderly patients as well as patients with co-morbid conditions such as vascular disease and diabetes mellitus in the hemodialysis (HD) population, a well functioning mature arteriovenous fistula (AVF) is essential for the delivering HD in these patients. [1],[2] Malfunction of permanent vascular accesses remains a cause of frequent and costly morbidity among these patients. [3]

Stenosis of the HD vascular access is common with an occlusion rate of 17–45% at one year. [4],[5] Therefore, periodic monitoring of the access is recommended; early detection and correction of stenotic lesions can reduce the frequency of thrombosis and the need for high-risk therapy, increase the life of the access and help to reduce the rate of access failure. [1],[5]

A variety of techniques such as physical examination, venous pump pressure, percent access recirculation, transonic flow and others are helpful in detecting vascular access dysfunction and improve assessment of the vascular access site. [4],[6] There is currently no consensus as to the optimum method of screening for stenosis; the most widely used method of screening for stenosis has been the percent access recirculation (%AR) measurement. [4]

Vascular access recirculation (AR) is defined as the return of dialyzed blood to the arterial segment of the access bypassing the systemic recirculation, thereby resulting in reducing the efficiency of dialysis. [7] High degrees of recirculation can lead to a significant discrepancy between the amount of HD prescribed and the amount of HD delivered.[8] Some investigators have suggested that AR of *15%* or higher reliably suggests significant stenosis. [4]

The usually method for recirculation measuring is the Doppler Effect and the different technical based in the circulation blood sense of through the needles. These procedures have the great advantage to be carried by the medical and infirmary personal.

At the moment some automatic systems estimate the recirculation rate with used hemodilutión technical that consist in the administration of saline serum in the return line,

Measuring System of Urea in Blood by Application in Recirculation for Hemodialysis Treatment 217

The study was practice in 37 patient's 15 males and 22 women, with ages 14 and 59 years and the time in hemodialysis treatment between 1 month and 4 years. Mean age of patients was 54.7±15 years, male 55.9±15.2 years and female 52.9±14.7 years. Causes of ESRD of our patients included high blood pressure, diabetes mellitus, glomeronephritis, obstructive

HD was performed for 3-4 Hrs, three times a week, using synthetic (polysulfone) dialyzer membranes, and bicarbonate-based dialysate at a delivered bicarbonate concentration of 35 mEq/L. Blood flow rate was maintained at 250-350mL/min, and the dialysate flow rate at 500 mL/min. Then the degree of recirculation was measured with Urea based two needle

The analytic form in the recirculation access is based in the urea molecule mensuration or BUN (Nitrogenous Urea in Blood) this estimation is quantified by in employment of the

> S A R x 100% S V

Arterial (A) and Venus (V) samples to same time and Peripheral (P) obtained with the slowstop-flow method; obtained A and V; the flow in peristaltic bomb to decrease at 50 ml/min, exactly 10 seconds. Then stop the bomb and immediately clampear the arterial line above the place samples extraction one the sample of blood S or systemic. Then the dialysis is restarted. It is the denominated method of the two needles. To make these determinations

1. The ultrafiltration was turned off approximately 30 minutes after the initiation of HD and then arterial and venous line samples (A and V in the above formula) were

2. Access blood flow was reduced to 50mL/min and 15 to 30 seconds later, the systemic blood sample (P in the above formula) from the arterial blood line was obtained (two-

3. The samples are reported via the laboratory and they are compared with those registered by On-Line system, we compared the statistical results the recirculation

We arranged optical custom measurement system based on photodiodes arrays connected to a PIC16F876 microcontroller, which implemented the acquisition and the physical interface between the optical sensors and the display and computer. The system is formed by an array of 128 photodiodes (Texas Instruments); the light source is a LED diode with a

S: Urea concentration in blood to take in Peripheral line a low fluid. A: Urea Concentration in blood to take in arterial line a constant fluid. V: Urea Concentration in blood to take in venous line a constant fluid.

recommending 5 to 30 minutes of initiate the dialysis. The following protocol was used for blood sampling.

(1)

uropathy, polycystic kidney and other causes.

method from the following formula (9):

**2.1 Two needles technique** 

following formulates.

obtained.

needle" techniques).

single wavelength of 620 nm.

percentage and the KT/V estimate.

**2.2 Online measurement system in blood urea** 

Where;

as well the employment of differences sensors in the arterial line for example; they measure of transmission the ultrasounds speed, the changes in the hematocrit conductivity or the temperature in blood.

The investment of lines also produces changes in the increases of the hematocrit induced by abrupt increments of the ultra filtration rate, constituting the base of our procedure to measure the flow of the vascular access.

There are hemodialysis monitors that incorporate the automatic reading of the ionic dialisance by conductivity analysis in the dialysis liquid. This measuring is effectuated to input and output in the dialysis filter. The ionic dialisance is equivalent to urea clearing (clearing of the dialyzed corrected by the total recirculation) that variation in the ionic dialisance is depends on the flow in the vascular access and it allows the calculation of the same one without having to dilute the blood by the administration of saline serum.

At the moment some automatic systems estimate the recirculation rate with used hemodilutión technical that consist in saline serum administration, as well the employment of differences sensors (ultrasounds, conductivity or the temperature) in the arterial line.

Example of the previous things is that some hemodialysis monitors that incorporate the automatic reading based of the ionic dialisance and conductivity analysis in the dialysis liquid.

This measuring is effectuated to input and output in the dialysis filter. The ionic dialisance is equivalent to urea clearing (clearing of the dialyzed corrected by the total recirculation) that variation in the ionic dialisance is depends on the flow in the vascular access and it allows the calculation of the same one without having to dilute the blood by the administration of saline serum.

We are studying the possibility to recirculation measure in fixed and permanent vascular access by On-Line mensuration of the Urea in blood (BUN) by employ the optical sensor in visible range, this results which compare by laboratory technical based in the method recirculation of two needles.

The purpose of the present study was to evaluate AR in chronic renal failure patients for early detection of access stenosis and subsequent intervention or revision to prolong the life of the access.

It is well established that one of cause of inadequate dialysis in HD patients is arterio-venous (A-V) fistula access recirculation (AR). Hemodialysis AR is diagnosed when dialyzed blood returning through the venous side reenters the dialyzer through the arterial needle, rather than returning to the systemic circulation and as a result, the efficiency of HD is reduced.(8) Thus the aim of the study was to investigate the prevalence and causes of A-V fistula recirculation in HD patients in Military Hospital Center in Mexico City.
