Assessment of hemodialysis adequacy in patients with chronic kidney disease in the hemodialysis unit at Tanta University Hospital in Egypt

Introduction

End-stage renal disease (ESRD) is an irreversible, condition for which patients require treatment with dialysis or kidney transplantation to survive.[1] It is a major outcome of chronic kidney disease with an important effect on the quality of life (QOL) and health resource utilization. In addition to costs, a large number of patients die of cardiovascular diseases prior to the initiation of renal replacement therapy (RRT).[2] Hemodialysis (HD) is one of the main modalities of RRT.[3]

Even though HD treatment is successful to ameliorate many of the clinical manifestations of ESRD and to postpone otherwise imminent death, HD patients still have higher mortality and hospitalization as well as lower QOL compared with the general population.[4]

The concept of quality, adequacy, or appropriateness of HD, which were introduced in the 1970s, implies dialysis which enables patients to have a normal QOL as well as solid clinical tolerance with minimal problems during the dialysis and interdialysis periods.[5] Quantification of the dialysis dose is an essential element in the management of chronic HD treatment because the adequacy of the dose has a profound effect on the patient morbidity and mortality.[6]

The aim of this work was to evaluate HD adequacy in patients with ESRD in the Hemodialysis Unit at Tanta University Hospital to identify the prevalence and causes of inadequate HD among those patients and the impact of adequacy on other parameters that affects patients’ outcomes as anemia, nutritional state, health-related QOL, and blood pressure.

Patients and Methods

This study was carried out on 100 stable patients with ESRD undergoing regular HD for more than 6 months. Patients who were on regular HD for 6 months (at least) using arteriovenous fistula (AVF) in Hemodialysis Unit at Tanta University Hospital. Patients who were not maintained on regular HD and patients use central venous catheters or arteriovenous grafts were excluded.

The patients were divided into two groups according to Kt/V values. Group I Included patients with Kt/V ≥1.2 who were considered to have adequate dialysis dose and group II hadpatients with Kt/V <1.2 (inadequate dialysis dose).

All patients were subjected to full history taking, complete physical examination, and laboratory investigations include blood urea nitrogen (BUN) (predialysis and postdialysis), serum albumin, hemoglobin (Hb) level, and urea reduction ratio (URR) using this formula:[7]

URR =(predialysis BUN – postdialysis BUN)/predialysis BUN

Kt/V calculation using the second generation Daugirdas formula:[8]

Single – pool Kt/V= −In (R −0.008 ×t) +(4 – 3.5 × R) × UF / W

Where In represents the natural logarithm, R is the ratio of postdialysis to predialysis BUN, t is the length of a dialysis session in hours, UF is the ultrafiltration volume in liters, and W is the patient's postdialysis weight in kilograms.

Calculation of vascular access recirculation using this formula:[9]

Recirculation % = ([S − A]/[S − V])× 100

S, A, and V refer to the systemic urea concentrations in the peripheral blood, blood entering the arterial line, and postdialyzer venous circuit, respectively.

Calculation of normalized protein catabolic rate (nPCR) using this formula:[10]

nPCR = (0.0136 × F) + 0.251

where

F = Kt/V ×([predialysis BUN+postdialysis BUN]/2)

HD prescription was revised to detect blood flow rate (BFR), ultrafiltration volume (UF volume), effective surface area of the dialyzer, and venous pressure.

Results

In Group I, the number of patients was 40 while the number of patients of Group II was 60. All patients in Group I (Kt/V ≥1.2) had URR ≥65% and those in Group II (Kt/V <1.2) had URR <65%. The correlation between dialysis dose (Kt/V) and URR is significant (P < 0.01) [Figure 1].

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Figure 1

Correlation between Kt/V and urea reduction ratio

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The age of the study population was 53.04 ± 14.7 years. The difference in clearance rates among the various age groups was statistically insignificant (P = 0.103). The highest clearance rates were observed among age group 31–45 years, which represent around 15% of the study population.

A strong association between higher clearance rates and increased dialysis duration of each session (4 h; 78.9%), frequency of dialysis per week (3 times/week; 46.8 %), and BFR (>300 ml/min; 63.3%) was noted and differences for both variables were statistically significant (P = 0.001, 0.012, and 0.003, respectively).

Discussion

Over the past ten years, published data indicated that survival of dialysis patients is strongly associated with delivered dialysis dose.[11] Improvements in the survival rates at higher dialysis doses were reported with all major causes of mortality including coronary heart disease, other cardiac diseases such as stroke and infection. This observation is compatible with the hypothesis that low doses of dialysis may promote atherosclerosis, infection, malnutrition, and failure to thrive.[12]

At present, HD dose is quantified by the Kt/V, which measures urea removal during treatment and a single pool Kt/V of 1.2 is considered as adequate dose.[13] The primary data from the National Cooperative Dialysis Study showed that Kt/V <0.8 was associated with a high morbidity, whereas Kt/V values between 1.0 and 1.2 were associated with better outcome.[6]

As regard dialysis adequacy, results of this study revealed that about 60% of the study population had Kt/V <1.2, indicating that patients were receiving inadequate dose.

These results were in agreement with similar findings to those carried out in other developing countries such as Brazil, Nigeria, Nepal, Pakistan, and Iran (about 55–65% of patients had a Kt/V <1.2).[14] On the other hand, the results of the present study were in disagreement with those reported from developed countries as the United States according to the 2007 annual report, over 90% of the patients had a Kt/V >1.2.[15]

As regard, the relationship between Kt/V and URR revealed that all patients with spKt/V ≥1.2 had URR ≥65%. These results were in agreement with Afshar et al.,[16] who found statistically strong correlation between URR and eKt/V (P < 0.001). On the other hand, our results were in disagreement with the study of De Oreo and Hamburger[17] who reported a poor correlation between URR and Kt/V in 942 patients when both values were measured simultaneously.

Increased BFR was found to associated with increased rate of clearance [Table 1]. This was clear from the findings of Kt/V values ≥1.2 (200–250 ml/min, 20%; 251–300 ml/min, 35.6%; more than 300 ml/min, 63.3%). The difference in clearance rates among the various groups of BFRs was statistically significant. These results were in agreement with the study of Kim et al.,[18] Borzou et al.,[19] Ward,[20] Port et al.[21] On the other hand, our results were in disagreement with the study of Ghali and Malik,[22] there was no significant effect of increasing BFR on HD adequacy. They assigned their results to the effect of other different factors affecting dialysis adequacy as malnutrition, anemia, short dialysis sessions, premature cessation of sessions of HD, infection, inadequate blood flow from vascular access, hypotension episodes, technical reasons, and the design of the study and the sample size.

Table 1 Comparison between Kt/V values in respect of BFRs

As regard the duration of HD session [Table 2], clearance was strongly association with an increased duration time of dialysis process. The difference in the clearance rates among the various duration periods were significant. These results were in agreement with the study of Lambie et al.,[23] who showed that time had a profound effect on dialysis adequacy, indicating the importance of ensuring that patients remain on dialysis for the full time prescribed.[15]

Table 2 Comparison between Kt/V values in respect of duration of dialysis session

As regard frequency [Table 3], we found improvements in the clearance rates with increased dialysis frequency. The were consistent with previous reports that link improvements in clearance rates and frequency of dialysis.[24]

Table 3 Comparison between Kt/V values in respect of frequency of sessions/week

As regard UF volume [Table 4], a clear trend of improvements in Kt/V values was seen with increased UF rate (within limits as decrease in clearance rate was noted in patients with UF volume >4 L). Few studies have examined the direct association of UF rate on long-term outcomes in HD patients. The National Co-operative Study on the adequacy of dialysis reported the association between excessive UF and mortality, independent of delivered Kt/V urea recently.[25]

Table 4 Comparison between Kt/V values in respect of UF volume/session

Improvements in Kt/V values increased the dialyzers [Table 5]’ surface area. These results were in agreement with the previous reports on the membrane size and clearance rates which were done by Stivelman et al.[26] and Pascual et al.[27] The use of larger surface area dialyzers permits high rates of urea clearance to be achieved offering the advantage of improving blood purification by removing higher and middle molecular – weight solutes.[27]

Table 5 Comparison between Kt/V values in respect of dialyzer's surface area

Low recirculation percentage would result in better dialysis adequacy [Table 6]. Differences in Kt/V values among these recirculation groups were statistically significant. These results were in agreement with Santoro[28] who concluded that the form of needle insertion and the distance between the needles should be considered to be the part of the process of recirculation reduction with the classical form presenting the lowest percentages of AR and with unidirectional needles providing satisfactory results as long as the distance between them is 5 cm or more.

Table 6 Comparison between Kt/V values in respect of percentage of AR

Diabetic and hypertensive nephropathy are the leading underlying etiologies of the ESRD.[29] Diabetes is the leading cause of the ESRD in developed countries, and it accounts for 45% of causes of kidney failure which increases from 18% in 1980.[30] According to Afifi et al.,[31] the prevalence of diabetic nephropathy among ESRD patients in Egypt increased from 8.9% in 1996 to 24.5% in 2003. The data of present study in this respect are consistent with worldwide percentage for the etiology of the ESRD.

Hypotension is one of the most common medical complications seen during the HD. Multiple factors are associated with intradialytic hypotension as excessive UF, anemia, antihypertensive medications, cardiac disease, and errors in the estimation of patient's dry weight.[32] In the current study, hypotension was found to be the most frequent complaint during dialysis treatments, the results showed that 23% of the study population complained of hypotension. These results were in agreement with Sherman.[33]

In the present study [Table 7], AVFs were the vascular access used in all study population as patients with arteriovenous grafts and central vein catheters were previously excluded. These results were in agreement with the 2006 update of Kidney Disease Outcomes Quality Initiative (K/DOQI) guidelines that consider the most distal site possible to permit the maximum number of future possibilities for access so; the radiocephalic fistula is the first choice of access type. Our results showed also that patients who were dialyzed from brachiocephalic fistula had the highest clearance rate (46.67% of them showed a Kt/V ≥1.2) in comparison with the other two groups. These results might be as the brachiocephalic fistula had the higher BFR and easier to cannulate in comparison with radiocephalic and brachiobasilic fistulas, respectively. However, differences in the clearance rates among the different types of AVFs were statistically insignificant (P = 0.594).

Table 7 Comparison between Kt/V values in respect of vascular access (types of AVFs)

The mean Hb was 10.66 ± 2.15 g/dl in patients of the present study [Table 8]. This value is lower than the recommended DOQI guideline that recommends an Hb of 11–12 g/l. The mean Hb in our study population was lower, compared to other countries: Mean Hb levels were 12 g/dl in Sweden; 11.6–11.7 g/dl in the United States, Spain, Belgium, and Canada; 11.1–11.5 g/dl in Australia, New Zealand, Germany, Italy, the United Kingdom, and France.[34] The factors responsible for the low Hb levels in our patients, compared to the DOQI guidelines and other countries’ Hb levels, are the following: Blood loss, lack of consistent supplies of erythropoietin, and insufficient dialysis dose. There is good evidence that dialysis adequacy has resulted in better control of anemia and other parameters correlating with dialysis adequacy such as hypertension and patients’ nutritional status.[35]

Table 8 Correlations between dialysis dose (Kt/V) and other variables

The positive correlation between albumin and adequacy is in agreement with the study of Azar et al.,[36] who showed a strong correlation between serum albumin and Kt/V. This finding suggests also that patients undergoing chronic HD adjust their protein intake automatically according to the dose of HD delivered, probably via an improvement in appetite as a result of the disappearance of uremic symptoms from the digestive system (e.g., nausea, anorexia, and vomiting).

Lindsay and Spanner[37] showed that any attempt to increase the protein intake in patients undergoing HD was unsuccessful if any previous increases in the amount of prescribed HD were not established first. They found also a linear positive correlation between Kt/V and nPCR.

We found a positive correlation between dialysis dose (Kt/V) and scoring of physical domain of WHOQOL-BREF while there was no correlation between dialysis dose (Kt/V) and psychological, social or environmental domain scores. These results were in agreement with the study of Manns et al.,[38] who found out that increase dialysis dose had been associated with a better QOL and the study of Benz et al.,[39] who found out that increase dialysis dose was associated with a decrease number of awakenings at night.

There was no correlation between dialysis dose (Kt/V)and blood pressure. These results were in agreement with the study of McGregor et al.,[40] who did not ascertain any correlation between Kt/V and blood pressure and the study of Rahman et al.,[41] who found out strong correlation between blood pressure and interdialytic weight gain. On the other hand, the results of the present study were in disagreement with Panagoutsos et al.,[35] who found out that a reduction in blood pressure with increased dialysis dose suggesting a central role of increased dialysis dose. Others have also reported similar findings with corresponding increase of dialysis dose.[42]

In summary, the findings of the present study showed clearly that with increasing time and frequency of dialysis, BFRs, low recirculation percentages, reduction of intradialytic complaints, and well-functioning vascular access were associated with better dialysis adequacy.

We recommend that, first, individualizing the HD prescription based on monthly assessment of single-pool Kt/V would be a useful and practical tool to provide a safe and cost-effective HD treatment, second, to ensure that ESRD patients treated with chronic HD receive adequate treatments; the delivered dose of HD needs to be measured monthly. HD centers should have a continuous quality improvement and patient review system in place that recognizes patients who are receiving suboptimal dialysis adequacy, identify the cause, and rectify it, if possible and to assess whether targets are achieved in accordance with DOQI guidelines in an effort to achieve improved long-term outcomes in patients on chronic HD.