Home About us Current issue Ahead of Print Back issues Submission Instructions Advertise Contact Login   

Search Article 
Advanced search 
Saudi Journal of Kidney Diseases and Transplantation
Users online: 173 Home Bookmark this page Print this page Email this page Small font sizeDefault font size Increase font size 

EDITORIAL Table of Contents   
Year : 1998  |  Volume : 9  |  Issue : 2  |  Page : 110-115
Adequacy of Hemodialysis: It is not Only Urea we Have to Monitor

Department of Medicine, King Faisal Specialist Hospital & Research Center, Riyadh, Saudi Arabia

Click here for correspondence address and email

How to cite this article:
Alfurayh O. Adequacy of Hemodialysis: It is not Only Urea we Have to Monitor. Saudi J Kidney Dis Transpl 1998;9:110-5

How to cite this URL:
Alfurayh O. Adequacy of Hemodialysis: It is not Only Urea we Have to Monitor. Saudi J Kidney Dis Transpl [serial online] 1998 [cited 2021 Apr 15];9:110-5. Available from: https://www.sjkdt.org/text.asp?1998/9/2/110/39281

   Introduction Top

Monitoring simply the predialysis blood urea nitrogen or predialysis serum­creatinine may not represent the quality and adequacy of hemodialysis delivered, since low values may only reflect poor nutrition and low dialysis dose. Neither can the clinical condition on its own be used; since this might be masked by correction of anemia and acidosis and late deterioration is expected if no correction of adequate dialysis is attempted. Therefore, a measure of the dose of hemodialysis delivered is necessary.

There is no doubt that the best indicator of the quality of treatment for patients requiring dialysis treatment is their survival. This reflects not only the dialysis treatment but also the whole medical care, nutrition, family support and social integration.

The best reported survival of patients on hemodialysis is the one from Tassin, France, with a 15-year survival of 65% of 445 patients followed between 1970 to 1990 [1] . This group is known to dialyze its patients extremely intensively and over long periods.

It is well known that hemodialysis patients in the USA run a higher risk of death than comparable patients in Europe. An example for a comparison that takes care of many comorbidities, such as age, diabetes and gender, is a study from Lombardy, Italy, where the relative risk of mortality for hemodialysis patients was 36% lower than that of patients treated in the US. It is interesting that this difference does not exist for CAPD [2], where patients from both regions receive the same dose of dialysis, which is not the case for hemodialysis.

Hemodialysis Dose and Survival:

A large number of studies have shown that survival of patients on hemodialysis is closely related to the dose of dialysis delivered [2],[3],[4] . As an explanation for the difference between the survival rate of the American and European hemodialysis patients, Held and colleagues considered the 20% larger surface area of dialyzers used in Europe and the 23% longer period of time the patients were on dialysis [5] . Patients dialyzed fewer than 3.5 hours per week had double the mortality risk as those dialyzed four or more hours [6] . The radical cut in the dialysis time in the United States was the result of the wide popularity of urea kinetic modelling in the last 10 to 15 years. This was developed as a result of the mechanistic analysis of a collaborative dialysis study [7] . A value of Kt/V above 0.9 was seen as an indicator for adequate dialysis. Patients with comorbidities and diabetes were not included. This value has been slowly increased over the past years, so that the accepted minimum­-Kt/V for classical dialysis was set at 1.2 and for high-flux-dialyzer at 1.4 [8] , or even at 1.4 and 1.6 respectively [9] . This is because it was determined that shorter dialysis was associated with poorer survival rate of patients on dialysis. This approach did not give consideration to the possibility of a better clinical outcome with higher Kt/V. It has been shown that an increase of Kt/V of 0.1 can lead to a decrease of mortality risk by 7% [4] . One has to apply a higher dialysis dose as a minimum for patients for another reason, namely the risk of falsely higher value of KT/V; which usually results from not adhering to the rules in performing the urea kinetic modelling.

Urea Kinetic Modelling:

Urea as a surrogate for small molecular weight solute clearance has been demonstrated by many studies to be an acceptable parameter of adequacy [10] . The application of the kinetic modelling of urea has been adopted in analogy to the pharmacokinetic equation representing the elimination of a drug from the body, which is the function of the distribution volume of that drug, the capacity of elimination, and time. The single compartment model is now a common method in many dialysis units, and there are computer programmes available to calculate the formula. Here we will not go into details of the method but concentrate rather on its pitfalls. The most important and common mistake is the early collection of urea after the end of dialysis, which leads to a falsely favorable value of urea. One has to wait at least 10-15 minutes after the end of dialysis to collect a non-diluted blood sample for urea to allow for the equilibration of the intra­and extra-vascular fluids [10] . This will also take care of the falsely low urea that results from fistula recirculation. This is especially necessary when dialysis time is short and a high efficacy dialyzer is used.

A popular formula for the estimation of delivered dialysis dose is as follows:

Kt/V - In (R - 0.03) + (4 - 3.5R) x UF/BW. In is the natural logarithm, available in scientific calculators, R is the ratio of post­and pre-dialysis urea, UF is the amount of ultrafiltrate removed during the dialysis session and BW is the dry weight of the patient*.

Kt/V can be calculated from the dialyzer clearance at the respective blood flow rate (which can be obtained from manufacturers) as dialyzer mass-transfer area coefficient (KoA) related to blood and dialysate flow rates, and dialyzer surface area. The effective dialysis time should also be calculated, (interruptions are to be considered). In addition, the distribution volume of urea should be calculated, and the result is an indicator for the theoretical estimation of Kt/V [11] .

Comparison between the delivered and the estimated Kt/V enables the clinician to uncover deficiency of dialysis. If the delivered KT/V is less than the calculated one the following reasons can be suspected:

  • The extra corporeal blood flow is less than that shown on the monitor.
  • The dialysis session is shorter than prescribed due to interruptions of the treatment or intermittent lowering of blood flow.
  • Access recirculation.

So a measurement of dialysis dose can help correcting failure of treatment. With the same formula the desired dialysis time to reach a target Kt/V can be calculated for each individual.

Prevention of Infection:

Adequate hemodialysis treatment does not stop at the estimation of the dose of dialysis, but other factors to maintain the quality of treatment and to ensure the safety of treatment have to be considered as well.

Prevention of infection is a major concern for health professionals working in the field of dialysis. Patients and care providers alike are at risk of acquiring an infection while staying in the dialysis area. Therefore every attempt should be made to avoid infections.

Universal precaution measures to protect patients and personnel against infection are mandatory [12],[14] . Furthermore, admini­strations of dialysis centers should provide the required equipment and materials; they must not compromise because of cost. The precautions are simple and very practical including hand-washing before handling any patient, wearing non-sterile gloves before performing any treatment of any patient, avoiding introducing blood or other body fluids into eyes or face of personnel. This can prevent infection, and sometimes may be the only way (e.g. hepatitis C virus). Monitoring the strict adherence to the accepted policy is the responsibility of personnel in the hemodialysis unit [15],[16] . The prevalence of hepatitis C in Saudi Arabia has reached an alarming rate [16] , so intensive attention must be given to this problem. Prevention of infection is certainly cost effective considering the sequallae such as hepatic cancer secondary to this infection or untransplantability of the infected patients.

Water Treatment:

Purity of water used in dialysis is also essential to maintain adequate dialysis [17] . Supervisors of dialysis units should be familiar with the operation and proper function of the equipment used in purification of water in their units. Regular and independent testing of the sterility and purity of the water is mandatory. If the water quality is not adequate, acute and chronic damage to the patients' health will result, considering that in each dialysis session more than 120 litters of contaminated water pass through the dialyzer and separated from the blood of the patient by a permeable membrane.

Dialysate and Dialyzers:

Correction of uremic acidosis is best achieved with bicarbonate rather than acetate buffer. It is known that acetate acts as vasodilator, and this is especially important with the use of large high-flux dialyzers. Furthermore, proper correction of acidosis has a positive impact on the nutritional status of hemodialysis patients [18] and on their parathyroid function [19] .

We have already indicated the need for individualized prescription of the dialysis dose. This means the need for various sizes of dialyzers to be available at the disposal of the nephroiogist, to choose from, for different patients. There should be at least three different sizes of dialyzers, preferably of biocompatible membrane, since they are less likely to stimulate immunological reactions [20] .

Using a highly permeable dialysis membrane requires dialysate free of bacterial contaminations and/or pyrogens because of the risks of back filtration of dialysate into the bloodstream of patients. Contamination of dialysate provokes chronic stimulation of the immune system [21] and causes hypersensitivity reactions, hypotension, headache and fever. It is therefore advisable to obtain sterile dialysate, when dialyzing with biocompatible highly permeable membranes, by ultrafiltering the, dialysate monthly with disposable polysulfone filters [22] .

Dietary Measures:

Providing the necessary education to maintain a strict diet, avoiding excesses of salt, potassium and phosphate is part of giving adequate treatment to the patients on hemodialysis. Regular inquiry and reminder of the dietary requirements are to be documented by the nursing staff and by trained dietitians. This helps avoiding risks on the survival and the well being of patients. If patients adhere well to low salt diet, the need to remove large amounts of fluid on each dialysis is avoided.

Dry weight:

Dynamic tuning of the dry weight to correct chronic fluid overload or hypovolumia is an important task to be accomplished regularly bearing in mind seasonal clothing, nutritional status changes, and other morbidities affecting body weight.

Estimating the dry weight of dialysis patients is based on clinical data, thereby running the risk of overestimation and chronic hypertension [23] or underestimation and hypotension. The objective radiological methods used with the exception of chest-x­ray, have not yet found general acceptance and are mostly non-practical. Therefore, tight monitoring of the patient's clinical findings, such as peripheral edema, hypertension and other signs of fluid overload, as well monitoring the patient's hemodynamics is essential. The volume ­controlled ultrafiltration devices in the modern dialysis machines help greatly in removing fluid without much effect on the hemodynamic stability of dialysis patients.


Regular revision of the patients' need for medications to correct complications of chronic renal failure should be an important part of the standard routine care in each dialysis unit. Anemia should be managed not only by administering erythropoietin, but also by correction of other factors that may worsen it such as iron deficiency, chronic infection and inadequate dialysis. Correction of anemia has a positive impact on the quality of life besides reducing the development of cardiomyopathy and survival of patients on hemodialysis [24] .

Other medications in common use in dialysis units are calcium compounds for the treatment of calcium deficiency in combination with vitamin D 3 , and for phosphate binding. This usually calls for regular insurance of compliance to low-­phosphate diet, and adjustments according to levels of serum calcium, mineralization of the bones and parathormone activity. Some even suggest that high serum-phosphate is enough reason to prolong the dialysis time even if the Kt/V is acceptable [25] .

Social Support:

The social support patients receive in dialysis units should be considered as part of the adequacy of treatment. It is necessary to ease the household and financial stress burdens imposed on our patients by attempting to solve them with the help of skilful social workers. This helps the patients coping with their disease and therapy.

In summary, there are many aspects relating to the adequate treatment of patients maintained on hemodialysis beyond the pure mathematical calculation of one metabolic product. It is not enough to monitor one aspect of this complex disorder. Other factors related to dialysis treatment, medications, nutrition, and social life of patients are also indispensable.

   References Top

1.Charra B, Calemard E, Ruffet M, et al. Survival as an index of adequacy of dialysis. Kidney Int 1992:41(5): 1286-91.  Back to cited text no. 1    
2.Marcelli D, Stannard D, Conte F, Held PJ, Locatelli F, Port FK. ESRD patient mortality with adjustment for comorbid conditions in Lombardy (Italy) versus the United States. Kidney Int 1996;50(3):1013-18.  Back to cited text no. 2    
3.Fenton S, Desmeules M, Copleston P, et al. Renal replacement therapy in Canada: a report from the Canadian Organ Replacement Register. Am J Kidney Dis 1995;25(1): 134-50.  Back to cited text no. 3    
4.Held PJ. Port FK, Wolfe RA; et al. The dose of hemodialysis and patient mortality. Kidney Int 1996;50(2):550-56.  Back to cited text no. 4    
5.Held PJ, Blagg CR, Liska DW, Port FK; Hakim R, Levin N. The dose of hemodialysis according to dialysis prescription in Europe and the United States. Kidney Int 1992;38;S16-21.  Back to cited text no. 5    
6.Held PJ, Levin NW, Bovbjerg RR, Pauly MV, Diamond LH. Mortality and duration of hemodialysis treatment. JAMA 1991;20:871-75.  Back to cited text no. 6    
7.Gotch FA, Sargent JA. A mechanistic analysis of the National Cooperative Dialysis Study (NCDS). Kidney Int 1985;28:526-34.  Back to cited text no. 7  [PUBMED]  
8.Owen WF Jr, Lew NL, Liu Y r Lowrie EG, Lazarus JM. The urea reduction ratio and serum albumin concentration as predictors of mortality in patients undergoing hemodialysis. N Engl J Med 1993:329:1001-6.  Back to cited text no. 8    
9.Gotch FA, Levin NW\ Port FK, Wolfe RA. Uehiinger DE. Clinical outcome relative to the ose of dialysis is not what you think: the fallacy of the mean. Am J Kid Dis 1997;30(1):1­15.  Back to cited text no. 9    
10.Daugirdas JT, Ing TS. Handbook of dialysis 2. Edition, Little, Brown and Company 1994 p 96.  Back to cited text no. 10    
11.Hazier TA, Schulman G. Adequacy of dialysis. Kidney Int Suppl 1997:62:396-­100.  Back to cited text no. 11    
12.Favero MS. Recommended precautions for patients undergoing hemodialysis who have AIDS or non-A. non-B hepatitis. Infect Control 1985:6:301-5.  Back to cited text no. 12    
13.Morales J Duran C, Artigas G, et al. Impact of prophylactic measures on prevalence of anti-HCV and viral genotypes m a dialysis unit [letter]. Nephrol Dial Transplant 1997;12{12):2805-7.  Back to cited text no. 13    
14.Caramelo C, Navas S, Alberola ML, Bermejillo T, Reyero A, Carreno V. Evidence against transmission of hepatitis C virus through hemodialysis ultra filtrate and peritoneal fluid. Nephron l994;66:470-3.  Back to cited text no. 14    
15.Alter HJ. Clinical, virological and epidemio-logical basis for treatment of chronic non-A, non-B hepatitis. J Hepatol 1990:11:S 19-25.  Back to cited text no. 15    
16.Huraib S, Al-Rashcd R. Aldrees A, et al.High prevalence of and risk factors for hepatitis C in haemodialysis patients in Saudi Arabia: a need for new dialysis strategies. Nephrol Dial Transplant l995;10:470-4.  Back to cited text no. 16    
17.Bommcr J. Ritz E. Water quality a neglected problem in hemodialysis. Nephron 1987:46:1-6.  Back to cited text no. 17    
18.Bergstrom J, Alvestrand A, Fiirst P. Plasma and muscle free amino acids in maintenance hemodialysis patients without protein malnutrition. Kidney Int 1990:38:108-14.  Back to cited text no. 18    
19.Letebvre A, de­-Venieijoul MC.Gueris J.Goldfarb B, Graulet AM. Morieux C. Optimal correction of acidosis changes progression of dialysis osteodystrophy. Kidney Int 1989;36:1112-8.  Back to cited text no. 19    
20.Schulman G r Haleim RM. Recent advances in the biocompatibility of hemodialysis membrane Neph Dial Transplant 1991;6:10-13.  Back to cited text no. 20    
21.Pertosa G, Gesualdo L. Bottalico D, Schena FP. Endotoxins modulate chronically tumour necrosis factor alpha and interleukm 6 release by uracmic monocytes. Nephrol Dial Transplant 1995;10:328-33.  Back to cited text no. 21    
22.Yamagami S, Adachi T, Sugimura T, et al. Detection of endotoxin antibody in long term dialysis patients. Int J Artif Organs 1990; 13:205-10.  Back to cited text no. 22  [PUBMED]  
23.Salem MM. Hypertension in the hemodialysis population: a survey of 649 patients. Am J Kidney Dis 1995;26:461-8.  Back to cited text no. 23  [PUBMED]  
24.Foley RN, Parfrey PS, Harnett JD, Kent GM, Murray DC; Barre PE. The impact of anemia on cardiomyopathy, morbidity, and mortality in end-stage renal disease. Am J Kidney Dis 1996;28:53-61.  Back to cited text no. 24    
25.Valderrabano F, Percz-Garcia R. Junco E. How to prescribe optimal haemodialysis. Nephrol Dial Transplant 1996;1:60-7.  Back to cited text no. 25    

Correspondence Address:
Osman Alfurayh
Department of Medicine, King Faisal Specialist Hospital & Research Center, P.O. Box 3354, Riyadh 11211, Riyadh
Saudi Arabia
Login to access the Email id

PMID: 18408284

Rights and Permissions


    Similar in PUBMED
    Search Pubmed for
    Search in Google Scholar for
    Email Alert *
    Add to My List *
* Registration required (free)  


 Article Access Statistics
    PDF Downloaded281    
    Comments [Add]    

Recommend this journal