Saudi Journal of Kidney Diseases and Transplantation

: 2009  |  Volume : 20  |  Issue : 1  |  Page : 49--56

The influence of maintenance quality of hemodialysis machines on hemodialysis efficiency

Ahmad Taher Azar 
 Department of Biomedical Engineering, Misr University for Science and Technology, 6th of October City, Egypt

Correspondence Address:
Ahmad Taher Azar
Azar Building, Ahmad Orabi Square, Menoufeya, Menouf


Several studies suggest that there is a correlation between dose of dialysis and machine maintenance. However, in spite of the current practice, there are conflicting reports regarding the relationship between dose of dialysis or patient outcome, and machine maintenance. In order to evaluate the impact of hemodialysis machine maintenance on dialysis adequacy Kt/V and session performance, data were processed on 134 patients on 3-times-per-week dialysis regimens by dividing the patients into four groups and also dividing the hemodialysis machines into four groups according to their year of installation. The equilibrated dialysis dose eq Kt/V, urea reduction ratio (URR) and the overall equipment effectiveness (OEE) were calculated in each group to show the effect hemodialysis machine efficiency on the overall session performance. The average working time per machine per month was 270 hours. The cumulative number of hours according to the year of installation was: 26,122 hours for machines installed in 1998; 21,596 hours for machines installed in 1999, 8362 hours for those installed in 2003 and 2486 hours for those installed in 2005. The mean time between failures (MTBF) was 1.8, 2.1, 4.2 and 6 months between failures for machines installed in 1999, 1998, 2003 and 2005, respectively. Statistical analysis demonstrated that the dialysis dose eq Kt/V and URR were increased as the overall equipment effectiveness (OEE) increases with regular maintenance procedures. Maintenance has become one of the most expedient approaches to guarantee high machine dependability. The efficiency of dialysis machine is relevant in assuring a proper dialysis adequacy.

How to cite this article:
Azar AT. The influence of maintenance quality of hemodialysis machines on hemodialysis efficiency.Saudi J Kidney Dis Transpl 2009;20:49-56

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Azar AT. The influence of maintenance quality of hemodialysis machines on hemodialysis efficiency. Saudi J Kidney Dis Transpl [serial online] 2009 [cited 2020 Dec 5 ];20:49-56
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The most widely used definition of the dose of dialysis is fractional clearance of body water for urea-the product of dialyzer urea clearance (K) and treatment time (t) divided by the urea dis­tribution volume (V), or Kt/V. [1],[2],[3],[4],[5] Not all hem­dialysis patients receive their prescribed dose of hemodialysis. [6],[7] Some studies suggested that only 50% of end- stage renal disease (ESRD) patients in Egypt actually receive their pres­cribed hemodialysis dose. [8]

The current K/DOQI guidelines recommend that the minimum delivered dialysis dose per session be a sp Kt/V of 1.2 or a URR of 65% for patients treated three times per week. [9] To achieve these targets, it was further recom­mended that the prescribed dialysis dose should be sp Kt/V of 1.3 or URR of 70%.

A variety of factors may result in the actual delivered dose of hemodialysis falling below the prescribed dose. [6],[9],[10],[11],[12],[13],[14] Common factors related to hemodialysis machine maintenance include low blood pump and dialysate flow rates, or underestimates of flow due to calibration errors and blood pump tubing collapse. In order to improve system availability and reliability, va­rious maintenance policies have been proposed based on different assumptions and conside­rations. System maintenance can be divided into three main categories preventive maintenance, predictive maintenance (PM) and corrective maintenance (CM). [15] Preventive and predictive maintenance are proactive strategies for avoi­ding equipment breakdowns. The preventive and predictive maintenance are very similar in concept with some differences in the criterion for determining the need for specific mainte­nance activities. Preventive maintenance repre­sents all the actions performed in order to operate a system at an acceptable level of per­formance by providing systematic inspection, detection, and prevention of incipient failures. Perfect preventive maintenance means that the system is restored to good as new condition. Imperfect preventive maintenance restores the system to a condition that is between "good as new" and "bad as old".

Corrective maintenance represents all the ac­tions performed as a result of failure to restore a system to acceptable performance level. The actual overall equipment effectiveness (OEE) can be calculated from maintenance software as a function of the equipment breakdowns and the down time rate. [16]

Maintenance and repairs can lead to unsafe conditions and reduced system performance. A strong preventive maintenance program can help in reducing the frequency of emergency and much corrective maintenance and helps utility managers be aware of, and plan for, capi­tal equipment replacement. [17]

Hemodialysis machine maintenance is extremely important in evaluation of adequacy of hemo­dialysis and in assessing dialysis session per­formance. The calibration of dialysate pump and blood pump during periodic maintenance is an essential component to delivering the pres­cribed hemodialysis treatment. It is important to know the dialysis machines (i.e., how they work?, are machines truly volumetric?, what is the facility's procedure to replace/repair hemo­dialysis machines?, who does machine mainte­nance?, how often is dialysis staff in serviced on machine issues?, and/or what is the facility's procedure for periodic maintenance?). The dia­lysate and blood pump must be kept in calib­ration in order to deliver the settings on the machine. The clock must be accurate for the dialysate and ultrafiltration time. Routine pre­ventative and annual maintenance is vital to provide a safe and adequate dialysis and must be conducted with careful attention and in a timely fashion. Proper setting of the dialysis machine to achieve the prescribed blood flow rate can also significantly impact adequacy over time. [18] Machine maintenance is extremely im­portant as the machine may indicate the correct blood flow rate (BFR); but, if not calibrated correctly, it may be delivering more or less.

 Patients and Methods

Data were processed on 134 dialysis patients (mean age 48.21 ± 13.38, 69 male, 65 female) on 3-times-per-week dialysis regimens. Three patients dropped out throughout the study. The overall study period was 12 months from January through December of 2006. An expe­rimental study with a comparison group was used. The patients were divided into four groups; group A (40 patients), group B (40 patients), group C (30 patients) and group D (24 patients).

The hemodialysis machines were also divided into four groups according to the year of ins­tallation. Group 1 represents the machines with low number of working hours (machines ins­talled in 2005); group 2 represents the machines of medium number of working hours with re­gular maintenance procedures (machines installed in 2003); group 3 represents the machines of high number of working hours with regular maintenance procedures (machines installed in 1998) and group 4 represents machines of high number of working hours with deferred mainte­nance procedures (machines installed in 1999). The group 3 was selected for machines installed in 1998 and group 4 for machines installed in 1999 to show if the equipment effectiveness depends on the working hours of machine or deferred maintenance procedures.

The 4 groups of patients were changed in the first 4 months and distributed in the 4 groups of hemodialysis machines to make replacements between groups and to assure that the variation in dialysis efficiency is only due to equipment efficiency. This means that each group of pa­tients was dialyzed three times by the same group of dialysis machines throughout the year. This sequence of measurement protocol is shown in [Table 1].

Each machine had its own maintenance record on which was registered all pertinent informa­tion. Thus, it is possible to see the condition of the machine, and perform the necessary main­tenance based on the historical record of the equipment. The overall equipment effectiveness was calculated for each machine.

For each patient, age, gender, height, type of vascular access, location of access, pre-weight, post-weight, pre-blood pressure, post-blood pressure, type of dialysate, weight gain and HD duration were recorded. The characteristics of patients are shown in [Table 2].

For the study period, the following dialysis parameters were unchanged: dialysis session time 240 min (machine start to machine stop), dialysate flow 500 mL/min, blood flow 300 mL/min, same dialysis membrane for each pa­tient (1.6 m 2 polysulfone), same dialysis machine (Fresenius 4008B), and same dialysate inclu­ding sodium, calcium, conductivity profile, and temperature.

For each patient three measurements were ob­tained each month: pre-dialysis BUN obtained from the arterial arterio-venous (AV) fistula needle prior to hemodialysis, post-dialysis BUN from the venous AV fistula needle immediately after cessation of HD, and equilibrated BUN from the venous AV fistula needle at 30 minutes after HD was completed. The URR was calcu­lated using the formula: (urea pre-urea post/urea pre × 100%). [19] Dialysis dose was measured by equilibrated Kt/V (Kt/V eq ). [20] The single-pool Kt/V (Kt/V s p) was determined from the Daugirdas second generation formula. [21] Kt/V eq = (1-0.47/t) × Kt/V sp + 0.02, [22] and Kt/V sp = In(R - 0.008 × t) + (4-3.5× R) × UF/W, where R is the urea post/urea pre (in fractions of 1), UF is the ultrafiltration volume in kg, t is treatment time in h, and W is the body weight in kg. URR and eq Kt/V were measured monthly for each group.

The estimated average failure rate is the pro­bability of a failure occurring during a stated period of time or cycle, and can be calculated as follows: [15]

Breakdown rate = Equipment breakdowns/Test times (Equation 1)

By identifying the failures and the origin of the repair of each machine, it is possible to eva­luate the mean time between failures (MTBF) of the four groups of hemodialysis machines. MTBF is an index commonly used in main­tenance, which evaluates the machines function according to maintenance actions. The recipro­cal of the breakdown rate is the average life (0). For repairable items, the average life is called the "mean-time-between failures" (MTBF). [15] The "test times or cycles" in equation 1 is often a combination of the times that the failed piece of equipment or system was operational plus the times to repair. The downtime, which is referred to as "maintainability", can be mea­sured in several ways: a) Active repair time in­cludes only time spent in diagnosis and repair. b) Total downtime is the sum of times spent in active diagnosis and repair, delays waiting for parts, technical support and administrative work, and preventive maintenance. OEE can be viewed as the percent of time that equipment would need to run at its maximum speed in order to attain the actual output of that tool or machine. Hence, the actual equipment effec­tiveness can be calculated as a function of maintainability and the equipment breakdown rate from the following equation: [16]

Actual Effectiveness of Equipment = (100­ - Breakdown rate-Down time rate) /100 (Equation 2)

The ratio of the actual equipment effectiveness to its theoretical maximum effectiveness deter­mines the effect of the equipment effectiveness on dialysis adequacy.

Statistical analysis

Statistical analysis was performed using SPSS 14.0 and NCSS 2004 software packages. Mean errors relative to reference values were com­pared by one way ANOVA test. The Student's t test was used for both paired and non-paired data. P values [2] ] (Equation 3)

Effect of overall equipment effectiveness on dialysis efficiency in the first four months is shown in [Table 4].

The statistical analysis revealed that the dia­lysis dose of each group of patients was re­duced when dialyzed by the group 4 machines (machines installed in 1999). For example, in group A patients, eq Kt/V was reduced by about 25.1 % from 1.35 in January when dialyzed by machines installed in 2005 to 1.01 in Feb. when dialyzed by machines installed in 1999 due to deferred maintenance procedures (p= 0.00001). On the other hand, in group D patients, eq Kt/V was improved by about 41.75 % from 0.95 in January when dialyzed by machines installed in 1999 to 1.34 in Feb. when dialyzed by ma­chines installed in 2005 (p= 0.00001).

The mean of eq Kt/V and URR of the four groups of patients throughout the year is shown in [Table 4]. The statistical analysis demonstrated that there was a significant improvement in the mean URR and Kt/V of group 1 machines com­pared to other groups (p= 0.00001), group 2 compared to group 3 (p= 0.00001), and group 3 compared to group 4 (p eq Kt/V and URR was calculated and compared to the mean value that was calculated in the previous four months. Three mean values of eq Kt/V and URR was calculated throughout the year and compared to each other. No statistically significant diffe­rences were noted between the three values of the mean eq Kt/V and URR. The box plots com­parisons of eq Kt/V and URR between four groups of machine are shown in [Figure 2A] and [Figure 2B].


Maintenance should not be seen as an unexpected or extra expense. It should be constantly monitored, as the impact generated is significant and tends to increase over time. Neglecting this variable can lead to incon­veniences and inappropriate conclusions about the equipment. It is evident that the older ma­chines maintained a cumulative functioning time greater than the newer machines. How­ever, the monthly mean was similar for the four groups in this study.

A more thorough analysis of the four results shows us that there was a small increase in working hours in the group of machines ins­talled in 2005 (group 1), evidenced by the cons­tant increase in patient demand at the clinic, at which the sessions were increased rapidly from 2 to 3 daily shifts.

The results also revealed that dialysis effi­ciency increases as the equipment effectiveness increases. Equipment deficiency leads to inade­quate dialysis session and high level of intra­dialytic complications. In this study, the wor­king hours of group 4 were less than group 3, and the OEE for group 3 was higher than group 4 due to the deferred and irregular maintenance procedures in group 4.

Another problematic index exists, which is the low mean time between failures (MTBF). In this study, the mean was less than 3 months in several machines installed in 1998 and 1999, or rather, a time less than the minimum interval between the PM procedures adopted by the clinic. The result should improve in the subse­quent years, following predictive maintenance procedures, which aim to constantly monitor all the machines. This evaluation should be ma­naged by the maintenance team, in such a manner to achieve the best possible control of maintenance costs.

Neglecting repairs to avoid incurring costs can provoke even more costly consequences. Equip­ment maintenance is inevitable; however, it should be controlled and monitored in a manner that optimizes the repair process. Not to per­form a repair to avoid cost can lead to conse­quences even more costly and damaging.

Expediting repairs is also not enough; it is necessary to foresee failures and schedule cor­rective repairs in such a manner that guarantees safer dialysis, and proceeds without unexpected interruption. The useful life of the equipment is directly dependent upon the maintenance cost generated, which is thus, associated with the safety provided for the patient. All the available evidence in hemodialysis patients confirms the close association between equipment efficiency and dialysis adequacy. For example, in group A patients in this study, URR was reduced by about 19.7% from 71.5% in January, when dia­lyzed by machines installed in 2005 to 57.5% in Feb., when dialyzed by machines installed in 1999 (p= 0.00001), due to deferred maintenance procedures and uncalibrated machines. Also in group D patients, URR was improved by about 29.0 % from 56.7% in January when dialyzed by machines installed in 1999 to 73.2% in Feb., when dialyzed by machines installed in 2005 (p= 0.00001).

In conclusion, the equipment effectiveness is considered to be interrelated to dialysis ade­quacy and patients' outcome.


The author thanks all medical staff at the neph­rology department in Ahmad Maher Teaching Hospital, Cairo, Egypt for their invaluable support during the course of this study. Special thanks are sent to the maintenance department inside the hospital that gave me the compu­tational aids and technical support to finish this study.


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