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Saudi Journal of Kidney Diseases and Transplantation
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RENAL DATA FROM ASIA - AFRICA  
Year : 2015  |  Volume : 26  |  Issue : 4  |  Page : 827-832
Solute clearance measurement in the assessment of dialysis adequacy among African continuous ambulatory peritoneal dialysis patients


1 Division of Nephrology, University of Witwatersrand, Charlotte Maxeke Johannesburg Academic Hospital, Johannesburg, South Africa; Department of Medicine, Bayero University, Aminu Kano Teaching Hospital, Kano, Nigeria
2 Division of Nephrology, University of Witwatersrand, Charlotte Maxeke Johannesburg Academic Hospital, Johannesburg, South Africa
3 Department of Chemical Pathology, University of Witwatersrand, Charlotte Maxeke Johannesburg Academic Hospital, Johannesburg, South Africa

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Date of Web Publication8-Jul-2015
 

   Abstract 

Solute clearance measurement is an objective means of quantifying the dose of peritoneal dialysis (PD). Despite continued debate on the interpretation and precise prognostic value of small solute clearance in PD patients, guidelines based on solute clearance values are common in clinical practice. There is limited information on the solute clearance indices and PD adequacy parameters among this predominantly low socioeconomic status PD population. We investigated the solute clearance among continuous ambulatory peritoneal dialysis (CAPD) patients at the Charlotte Maxeke Johannesburg Academic Hospital and its relationship with other parameters of PD adequacy. Seventy patients on CAPD were studied in this cross-sectional study. Solute clearance was assessed using urea clearance (Kt/V). Linear regression analysis was used to determine factors associated with solute clearance, while analysis of variance was used to test the influence of weekly Kt/V on blood pressure (BP), hemoglobin (Hb) and other biochemical parameters. The mean age of the study population was 37.9 ± 12.4 years, 43% were females and 86% were black Africans. The mean duration on CAPD was 19.7 ± 20.8 months. Mean systolic and diastolic BP were 144 ± 28 and 92 ± 17 mm Hg, respectively. The mean Hb was 11.1 ± 2.2 g/dL and the mean weekly Kt/V was 1.7 ± 0.3. Factors like systolic BP, Hb level, serum levels of cholesterol, calcium, phosphate, parathyroid hormone and albumin were not significantly associated with the weekly Kt/V. We conclude that the dose of PD received by the majority of our patients in terms of the weekly Kt/V is within the recommended values and that this finding is significant considering the low socioeconomic background of our patients. There is no significant association between Kt/V and other indices of dialysis adequacy.

How to cite this article:
Abdu A, Naidoo S, Malgas S, Naicker JT, Paget G, Naicker S. Solute clearance measurement in the assessment of dialysis adequacy among African continuous ambulatory peritoneal dialysis patients. Saudi J Kidney Dis Transpl 2015;26:827-32

How to cite this URL:
Abdu A, Naidoo S, Malgas S, Naicker JT, Paget G, Naicker S. Solute clearance measurement in the assessment of dialysis adequacy among African continuous ambulatory peritoneal dialysis patients. Saudi J Kidney Dis Transpl [serial online] 2015 [cited 2022 Jan 26];26:827-32. Available from: https://www.sjkdt.org/text.asp?2015/26/4/827/160228

   Introduction Top


Adequacy of dialysis is an important factor in determining the overall prognosis of the peritoneal dialysis (PD) patient. Adequate dialysis is defined as the dose of dialysis associated with acceptable morbidity and mortality, while optimum dialysis is defined as the level beyond which the added clinical benefit is not worth the additional patient effort or cost. [1]

Solute clearance is an objective means of quantifying the delivered dose of PD. There has been an evolution of clinical guidelines on the target dose of PD based on the solute clearance to ensure the provision of adequate dialysis for optimal patient survival. [2],[3],[4] It has been suggested that due to variations in population characteristics, individual dialysis units should establish their own target level, ensuring that the minimal recommended dose is delivered to the patient and that solute clearance should be assessed during the first month of initiating PD and at least every four months subsequently. [2] In addition, it has been recommended that assessment of the adequacy of PD should include other parameters such as the fluid balance, blood pressure (BP) control, anemia management, bone and mineral metabolism and nutritional status. [2],[3],[4]


   Patients and Methods Top


This work was a cross-sectional study conducted on 80 end-stage renal disease (ESRD) patients on continuous ambulatory peritoneal dialysis (CAPD) managed at the PD Unit of the Charlotte Maxeke Johannesburg Academic Hospital (CMJAH). The study was approved by the Human Research Ethics Committee of the University of Witwatersrand. Using a semi-structured interview form, information on age, race, gender, etiology of CKD, duration on PD, type of PD solution, number of exchanges per day and erythropoietin dose was obtained. Clinical examination was also conducted and the BP was recorded.

Patients were given adequate information on the procedure and accurate method for complete collections of both the 24-h urine and the 24-h dialysate samples. Those patients without residual renal function (defined as having <100 mL of urine over a 24-h period) [2] did not collect 24-h urine specimens. Bottles were supplied for urine collection, which started one day prior to the next clinic visit. Patients brought their 24-h urine collections as well as their collections of the previous day's drained dialysate on the morning of the clinic visit. In addition, their overnight dwells were collected and blood sampled for plasma urea, creatinine (lithium heparin collection tubes) and hemoglobin (Hb) (EDTA tubes). The volumes of the 24-h collections of urine and drained dialysate were recorded and, after thorough mixing, 10 mL aliquots of each were taken. All participants' samples were analyzed at the CMJAH National Health laboratory Service. The samples for urine and dialysate urea and plasma urea and creatinine were analyzed on the Roche Modular P800 Chemistry system analyzer (Roche Diagnostics, Mannheim, Germany) and for Hb on the Beckman Coulter LH 750 Hematology analyzer (Beckman Coulter International SA, Switzerland). Other biochemical tests such as serum calcium, phosphate, parathyroid hormone, cholesterol and albumin were also analyzed as part of the patient's monthly routine workup. Solute clearance was assessed using urea clearance as defined by Kt/V. In patients with residual renal function, the total solute clearance (total Kt/V), which is the combination of the peritoneal and renal clearances, was used.

Kt/V = total Kt/V
Total Kt = peritoneal Kt + renal Kt
Peritoneal Kt = 24-h dialysate urea/plasma urea
Renal Kt = 24-h urine urea/plasma urea

Where V is the volume of distribution of urea obtained using the Watson formula. [5]

Linear regression analysis was used to determine factors associated with solute clearance while analysis of variance was used to test the influence of weekly Kt/V results on blood pressure, Hb and other biochemical parameters such as cholesterol, calcium, albumin, phosphate and parathyroid hormone. Statistical analyses were performed using computer-based software, Minitab for windows.


   Results Top


In this cross-sectional study, 80 patients on CAPD were studied; however, complete data was only available for 70 patients. They consisted of 60 (86%) black and ten (14%) nonblack patients. Thirty (43%) were females while 40 (57%) were males. The mean age of the study population was 37.9 ± 12.4 years, with a range of 18-65 years. Only 11 (15.7%) were employed among the study patients.

The mean duration on CAPD was 19.7 ± 20.7 months, with a range of 2-47 months. The mean diastolic BP was 92 ± 17 mm Hg, with a range of 53-145 mm Hg, while the mean systolic BP was 144 ± 28 mm Hg, with a range of 95-231 mm Hg. Systolic BP of 140 mm Hg or less was noted in 42.3% of the patients while 45.1% had a diastolic BP of 90 mm Hg or less. The mean Hb was 11.1 ± 2.2 g/dL, with a range between 7.2 g/dL and 17.9 g/dL. A target Hb of 11-12 g/dL was achieved in 39 (56%) of the study patients. Thirty-eight (54%) of the patients were on subcutaneous recombinant human erythropoietin injections with a weekly dose ranging between 4000 and 18,000 IU.

Hypertension was the most common cause of ESRD in the study population (46.5%). Others had diabetes mellitus (7%), glomerulonephritis (7%), congenital disease (12.7%) and unknown causes (22.5%). Four of the patients were positive for human immunodeficiency virus (HIV), but none were histologically confirmed cases of HIV-associated nephropathy (HIVAN). Three of the patients had previous renal transplants.

Eight patients had significant residual renal function, with a mean renal Kt of 3.1 ± 1.7. The mean volume of distribution (V) was 36.0, with a range between 25.2 and 53.4, while the mean 24-h dialysate volume was 9.6 ± 1.3 L, the mean 24-h dialysate urea was 22.8 ± 7.3 mmol/L and the mean 24-h D/P urea was 0.9 ± 0.1.

The mean Kt/V was 1.72 (within the recommended value in the major international guidelines); however, 32 (45.71%) of the patients had a weekly Kt/V of <1.7. The linear regression analysis result showed that there were no significant associations between the weekly Kt/V results and factors like duration on CAPD (coefficient β = 0.00, t = 0.47, P = 0.64), systolic BP (coefficient β = -0.10, t = -0.78, P = 0.44, Hb level (coefficient β = 0.08, t = 0.58 P = 0.56), serum cholesterol (coefficient β = 0.09, t = 0.67, P = 0.50), albumin (coefficient β = -0.23, t = -1.64, P = 0.11), calcium (coefficient β = 0.00, t = 0.04, P = 0.97), phosphate (coefficient β = 0.03, t = 0.52, P = 0.61) and parathyroid hormone level (coefficient β = -0.00, t = -1.47, P = 0.15).

The study patients were grouped into three groups based on the weekly Kt/V results. Those with weekly Kt/V values below 1.7 (n = 32) were classified as group 1, while those with values between 1.7 and 2.0 formed group 2 (n = 24) and those with values above 2.0 formed group 3 (n = 14). Analysis of variance (ANOVA) was used to test for any significant difference between the three groups in terms of the clinical and laboratory parameters, including the duration on PD, diastolic and systolic BP, plasma urea and creatinine, serum albumin, cholesterol and Hb. There was no statistically significant difference in all the parameters tested among the three groups [Table 1].
Table 1: Analysis of variance between the different groups based on the weekly Kt/V.

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   Discussion Top


The assessment of the PD adequacy in these patients has not been reported previously. Despite the continued debate on the interpretation and precise prognostic value of small solute clearance in PD patients, dialysis recommendations based on Kt/V have gained acceptance in clinical practice with the issuance of practice guidelines on the target dose of PD based on the Kt/V value achieved. [2],[3],[4]

The studied patients were predominantly black Africans, which is a reflection of the general population demographics within the Republic of South Africa (RSA). Majority of the patients studied were unemployed and even among those employed, many were self-employed; this is the reflection of the practice in RSA as most of the patients in public hospitals are likely to be those without medical aid coverage. Many of those with good jobs are found in the private sector, as their medical insurance schemes will provide cover for their treatment.

The patients studied were young, with a mean age of 37.9 ± 12.4 years, a reflection of the selection criteria for renal replacement therapy (RRT) in RSA; this is similar to the findings by others. [6] It has been reported that ESRD patients in sub-Saharan Africa are usually young and in their economically productive life. [7] However, the relatively young age of the patients may also be due to the fact that in RSA patients who are older than 60 years, patients with advanced cardiovascular disease and diabetic patients with cardiovascular disease are not accepted onto the public sector chronic dialysis programs because of limited resources. There was a slight male preponderance. This gender distribution differs with that reported in a similar study in Durban [6] in which two-thirds of the patients were male. The mean duration on CAPD was similar to that reported in a similar study in RSA. [6]

Residual renal function is known to influence patient survival as well as dialysis adequacy. [8] However, only eight of the patients studied had significant residual renal function and they had higher weekly Kt/V. This may be due to late presentation or as a result of long duration of disease, as CKD is known to be a progressive disease.

Solute clearance was measured in the form of Kt/V and not the creatinine clearance as recent major international guidelines no longer recommend the use of creatinine clearance as a measure for dialysis adequacy. [2],[3],[4]

Fifty-four percent of the patients studied had a Kt/V of >1.7 as recommended by the major international practice guidelines. [2],[3],[4] This is lower than 76% reported in an earlier study at Durban, RSA. [6] More than half of the patients studied achieved the recommended Kt/V target. This is relevant because many of the patients studied were of low socioeconomic background, as most patients in public sector facilities are those with no medical insurance cover and are mostly unemployed. The mean of the bone mineral metabolism indices of the study patients based on the serum calcium, phosphate and intact parathyroid hormone are within the levels recommended in major guidelines. Studies in the USA and Europe did not find a significant difference in the urea kinetic parameters among different ethnic groups. [9],[10]

Linear regression analysis was used to quantify the relationship between the weekly Kt/V values as a dependant variable and other factors such as the BP, Hb level, serum cholesterol and serum albumin, calcium, phosphate and parathyroid hormone level. There was no significant relationship observed between these parameters and the weekly Kt/V. Latiff et al [6] in a similar study using Spearman's correlation coefficient did not find a significant correlation between weekly Kt/V, BP, Hb level and other parameters, although in their study they used a computer-based kinetic modeling program to determine the Kt/V.

The studied patients were grouped into three groups: Those with weekly Kt/V below 1.7, those with values between 1.7 and 2 and those with values above 2.0. Analysis of variance (ANOVA) was used to study the differences between these groups in terms of other parameters like the Hb, BP control and biochemical indices of nutrition and mineral metabolism. There was no significant difference between the three groups in the various parameters. In a prospective study among Hong Kong CAPD patients, Lo et al [11] did not find differences between similar groupings in terms of mortality. Latiff et al [6] grouped their patients into two, those with Kt/V below 1.7 and those with Kt/V above 1.7, and found no significant difference between the two groups in terms of BP control, Hb, serum urea, creatinine and other parameters.

Among the limitations of this study is its cross-sectional nature; therefore, it was not designed to study the long-term effect of small solute clearance on patient outcomes such as morbidity, technique survival and mortality. Small solute clearance as a sole marker of PD adequacy has been challenged following the release of large randomized controlled trials such as the adquacy of peritoneal dialysis in Mexico (ADEMEX) and the Hong Kong studies. [12],[13] However, studies have shown that small solute clearances become important determinants of both patient and technique survival in anuric PD patients. [11] Several other studies have shown the effects of small solute clearance on survival in anuric PD patients. [11],[14] Considering the fact that majority of our CAPD patients are anuric, it is important to monitor the small solute clearance regularly as recommended by major international guidelines. [2],[3],[4]


   Conclusion Top


We conclude that more than half of our CAPD patients met the target in terms of the small solute clearance measure of Kt/V as recommended by major international practice guidelines and Kt/V is not significantly associated with other biochemical indices of dialysis adequacy. Regular monitoring of small solute clearance is recommended to ensure that patients are receiving an adequate recommended dialysis dose.

Conflict of interest: None declared.

 
   References Top

1.
Churchill DN. An evidence based medicine approach to determining the adequacy of peritoneal dialysis. Nephrology 1996;2 Suppl 1: S155-8.  Back to cited text no. 1
    
2.
K/DOQI Clinical Practice Guidelines for Peritoneal Dialysis. Am J Kidney Dis 2006;47 Suppl 4:s1-s47.  Back to cited text no. 2
    
3.
European Best Practice Guidelines for peritoneal dialysis. Nephrol Dial Transplant 2005; 20 Suppl 9:3-24.  Back to cited text no. 3
    
4.
Blake PG, Bargman JM, Brimble KS, et al. Clinical Practice Guidelines and Recommendations on Peritoneal Dialysis Adequacy 2011. Perit Dial Int 2011;31:218-39.  Back to cited text no. 4
    
5.
Watson PE, Watson ID, Batt RD. Total body water volumes for adult males and females estimated from simple anthropometric measurements. Am J Clin Nutr 1980;33:27-39.  Back to cited text no. 5
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6.
Latiff GH, Naicker S, Seedat YK, Nell G. Assessing the adequacy of continuous ambulatory peritoneal dialysis (CAPD). Saudi J Kidney Dis Transplant 1996;7 Suppl 1:s116-s9.  Back to cited text no. 6
    
7.
Arogundade FA, Barsoum RS. CKD prevention in Sub-Saharan Africa: A call for governmental, nongovernmental, and community support. Am J Kidney Dis 2008;51:515-23.  Back to cited text no. 7
    
8.
Lysaght MJ, Vonesh EF, Gotch F, et al. The influence of dialysis treatment modality on thedecline of remaining renal function. ASAIO Trans 1991;37:598-604.  Back to cited text no. 8
    
9.
Raj DS, Langos V, Gangam N, Roscoe J. Ethnic variability in peritoneal equilibration test and urea kinetics. Am J Kidney Dis 1997; 30:374-81.  Back to cited text no. 9
    
10.
Bakewell A, Higgins R, Edmunds M. Nutrition, adequacy of dialysis, and clinical outcome in Indo-Asian and White European patients on peritoneal dialysis. QJM 2002;95:811-20.  Back to cited text no. 10
    
11.
Lo WK, Lui SL, Chan TM, et al. Minimal and optimal peritoneal Kt/V targets: Results of an anuric peritoneal dialysis patient's survival analysis. Kidney Int 2005;67:2032-8.  Back to cited text no. 11
    
12.
Paniagua R, Amato D, Vonesh E, et al. Effects of increased peritoneal clearances on mortality rates in peritoneal dialysis: ADEMEX, a prospective, randomized, controlled trial. J Am Soc Nephrol 2002;13:1307-20.  Back to cited text no. 12
    
13.
Lo WK, Ho YW, Li CS, et al. Effect of Kt/V on survival and clinical outcome in CAPD patients in a randomized prospective study. Kidney Int 2003;64:649-56.  Back to cited text no. 13
    
14.
Davies SJ. Peritoneal solute transport - We know it is important, but what is it? Nephrol Dial Transplant 2000;15:1120-3.  Back to cited text no. 14
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Correspondence Address:
Aliyu Abdu
Department of Medicine, Bayero University, Aminu Kano Teaching Hospital, P.M.B 3452, Kano, Nigeria

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DOI: 10.4103/1319-2442.160228

PMID: 26178569

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