**2. Material and methods**

From February 2008 to August 2009, this cross sectional study was conducted on adult ESRD (End-stage Renal Disease) patients in HD of Military Hospital Center, Mexico City. A standardized questionnaire was used to collect demographic data, cause of ESRD, the date of HD onset, the type of access for HD, the date of creation and use of A-V fistula and history of a kidney transplant.

The ESRD was defined as permanent and irreversible loss of renal function requiring renal replacement therapy. They were included in the work all the patients in the Hemodialysis program in the Military Hospital Centre.

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 uropathy, polycystic kidney and other causes.

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 method from the following formula (9):

#### **2.1 Two needles technique**

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 following formulates.

$$\text{IR} = \frac{\text{(S} - \text{A)}}{\text{(S} - \text{V)}} \times 100\% \tag{1}$$

Where;

216 Technical Problems in Patients on Hemodialysis

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

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

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

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

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

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

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

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

From February 2008 to August 2009, this cross sectional study was conducted on adult ESRD (End-stage Renal Disease) patients in HD of Military Hospital Center, Mexico City. A standardized questionnaire was used to collect demographic data, cause of ESRD, the date of HD onset, the type of access for HD, the date of creation and use of A-V fistula and

The ESRD was defined as permanent and irreversible loss of renal function requiring renal replacement therapy. They were included in the work all the patients in the Hemodialysis

fistula recirculation in HD patients in Military Hospital Center in Mexico City.

same one without having to dilute the blood by the administration of saline serum.

temperature in blood.

liquid.

saline serum.

of the access.

recirculation of two needles.

**2. Material and methods** 

history of a kidney transplant.

program in the Military Hospital Centre.

measure the flow of the vascular access.

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.

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 recommending 5 to 30 minutes of initiate the dialysis.

The following protocol was used for blood sampling.


#### **2.2 Online measurement system in blood urea**

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 single wavelength of 620 nm.

Measuring System of Urea in Blood by Application in Recirculation for Hemodialysis Treatment 219

Fig. 2. Experimental Prototype by using PIC16F8767 Microcontroller and connection in the

The optical system consists on a small dark chamber where the source of light (LED) and the semiconductor device used as sensor (photodiode array) are placed. They are located lengthwise regarding the probe of transparent plastic through which the liquid samples are passed. The linear disposition of photodiodes gives a better rejection of stray light conduced

photodiode during a controlled time is used as the input signal of the 10 bit microcontroller A/D converter. The captured data are then transmitted via RS-232 to a personal computer; this date is used to calculations urea concentration. Finally the parameters they show in the

through the tube walls. The voltage resulting of integrating the current of each

Hemodialysis machine **B. Operation Mode** 

graphics interface.

Fig. 1. Schematic diagrams the on line system for urea in blood and LabView programming to connection a PC via RS-232 Protocol used in recirculation measurement during Hemodialysis treatment.

The physical construction system consists on a small dark chamber where the source of light (LED) and the semiconductor device used as sensor (photodiode array) are placed. They are located lengthwise regarding the probe of transparent plastic through which the liquid samples are passed. The linear disposition of photodiodes gives a better rejection of stray light conduced through the tube walls. The voltage resulting of integrating the current of each photodiode during a controlled time is used as the input signal of the 10 bit microcontroller A/D converter. The captured data are then transmitted via RS-232 to a personal computer.

The user interface is developed with Visual Basic ver.6.0, and Lab view Programming performing the data graphical representation to determination the constant of the time.

#### **A. On line Recirculación Systems**


Fig. 2. Experimental Prototype by using PIC16F8767 Microcontroller and connection in the Hemodialysis machine

#### **B. Operation Mode**

218 Technical Problems in Patients on Hemodialysis

Fig. 1. Schematic diagrams the on line system for urea in blood and LabView programming

The physical construction system consists on a small dark chamber where the source of light (LED) and the semiconductor device used as sensor (photodiode array) are placed. They are located lengthwise regarding the probe of transparent plastic through which the liquid samples are passed. The linear disposition of photodiodes gives a better rejection of stray light conduced through the tube walls. The voltage resulting of integrating the current of each photodiode during a controlled time is used as the input signal of the 10 bit microcontroller A/D converter. The captured data are then transmitted via RS-232 to a

The user interface is developed with Visual Basic ver.6.0, and Lab view Programming performing the data graphical representation to determination the constant of the time.

1. Oscillator: The oscillator used to generate a Sine wave, was the bridge Howland composed at four resistance and two capacitors. The configuration its low distortion

2. Tranconductance amplifier (OTA): Generate the current in LED (light-emitting diode),

3. Instrumentation Amplifier (IA): AD624 instrumentation amplifier. The tension in the optical sensor (Array 128 photodiodes) adds to Voltage continuous in 1.25 V. 4. Filtered / Conditioning: The filter function is used TL081 Operational amplifiers, for

5. Microcontroller: PIC16F876 microcontroller, with the internal A/D converter for Sine

and effective stabilization amplitude, used the TL081 circuit.

is implemented to LM3080 circuit, which has a gain control.

signal Voltage, and transmission RS-232 communication protocol.

to connection a PC via RS-232 Protocol used in recirculation measurement during

Hemodialysis treatment.

personal computer.

**A. On line Recirculación Systems** 

passes band filter in 45-55 KHz.

The optical system consists on a small dark chamber where the source of light (LED) and the semiconductor device used as sensor (photodiode array) are placed. They are located lengthwise regarding the probe of transparent plastic through which the liquid samples are passed. The linear disposition of photodiodes gives a better rejection of stray light conduced through the tube walls. The voltage resulting of integrating the current of each

photodiode during a controlled time is used as the input signal of the 10 bit microcontroller A/D converter. The captured data are then transmitted via RS-232 to a personal computer; this date is used to calculations urea concentration. Finally the parameters they show in the graphics interface.

Measuring System of Urea in Blood by Application in Recirculation for Hemodialysis Treatment 221

The direct results obtained with the prototype display the optical transmittance in the range of 600-620 nm, corresponding to a Red LED show the evolution in the urea concentration estimated during the experimental Hemodialysis procedure in a patient. In the Figure 4 show the recirculation evolution of the urea concentration during Hemodialysis treatment

To verify the functioning system, we comparing the urea concentration values obtained with the online prototype values versus Laboratory. Successive measurements under same

The results obtained with optical system and Laboratory (Dade Behring equipment) was coherent. In the Figure 5 we can observe that statistic factor between laboratory and prototype for recirculation percentage in Permanent Vascular Access (PVA). The average estimation for recirculation percentage impermanent accesses via laboratory is 3.57 ± 2.28 %, with optical system is 4.55±2.35%The Figure 6 we can observe that statistic estimation for

The average accesses via laboratory is 6.25 ± 4.16 %, with optical system is 8.77±5.13%. The show results indicate good correlation in average and standard deviation, the equal forms both measurement systems show wide dispersion The correlation coefficient between optical system and laboratory in the recirculation measurement in permanent accesses is R²

Fig. 4. Recirculation measurement by optical system, the calculation is based in the voltages estimation during Hemodialysis Treatment, Peripheral (S), Arterial (A) and Venous (v)

conditions (connectors, power, temperature, etc.) observing a small dispersion.

recirculation percentage in Permanent Hemodialisys Catheter (PHC)

**3.1 Experimental system** 

**3.2 Clinical measurements** 

in a patient shows values in the A-V fistula.

= 0.69 was temporary accesses R² = 0.66

blood samples when two needles technique.

Fig. 3. Experimental systems with both the optical absorbance probe in patients in hemodialysis treatment.

### **2.3 Measure process of urea concentration in blood in laboratory technical**

We used the two needles technique for the recirculation measure in the vascular access. In hemodialysis session, the flow in the vascular access is measured by employs the optical sensor for practice the on-line measure of Urea in blood and blood samples for evaluation in laboratory.

To treatment started the flow is the 400 ml/min after 30 min. We proceed to taking of samples in blood in the arterial (A) and venues (V) line in a simultaneous way, next time diminishes the flow to 50 ml/min during 30 seconds, which this proceeds to a second blood sample in the arterial line (S), concluded this activity with continues the hemodialysis session to the arterial flow prescribed.

The all measurements samples were evaluated in laboratory and on line measurement prototype for urea in hemodialysis treatment. The patients were divided into two groups, group 1 patients without recirculation and group 2 patients with recirculation.

For each patient distances between arterial and venous needles and distances of needles from A-V fistula and its directions was recorded. The findings were analyzed by SPSS statistical program. Chi square test or Fisher Exact test were used for qualitative data. For two group's quantitative data, the means were compared by using student's t test.

Association between risk factors and recirculation rate was evaluated by COX regression model. Statistical significance was assessed at the 0.05 probability level in all analyses.
