Dialysis


Hemodialysis Adequacy, Dialysate Composition in Hemodialysis, and Hemodialysis Access—A Compendium


Gautam Phadke, MD and Madhukar Misra, MD, FRCP(UK), FACP, FASN Division of Nephrology, University of Missouri, Columbia


Abstract


In the last two to three decades patient care in end-stage renal disease (ESRD) has improved substantially; various advances in dialysis technology have been made from online generation of dialysate, availability of ultrapure water, precise ultrafiltration control, and improvements in home hemodialysis. This article will address three major factors related to the care of the hemodialysis patient: the concept of adequacy as it stands in 2010, the importance of dialysate, and, finally, the ‘Achilles’ heel’ of HD—vascular access.


Keywords


Hemodialysis adequacy, uremic toxins, time-averaged solute concentration (TAC), National Cooperative Dialysis study, Kt/V, body surface area-normalized glomerular filtration rate (GFR), ultrapure water, sodium profiling, catheter-related bacteremia


Disclosure: The authors have no conflicts of interest to declare. Received: June 25, 2010 Accepted: September 21, 2010 Citation: US Nephrology, 2010;5(2):65–70 Correspondence: Madhukar Misra, MD, FRCP(UK), FACP, FASN, Professor of Clinical Medicine, Room CE 420, CSE Building, One Hospital Drive, Columbia, MO 65212. E: misram@health.missouri.edu


In the US, the relative risk for mortality in end-stage renal disease (ESRD) patients is 15% higher than Europe, and 35% higher than Japan (after adjustment for age and diabetes).1


However, advances in dialysis


technology, i.e. better-designed dialyzers, ultrapure dialysate, and intra- dialytic monitoring devices have failed to influence long-term survival of ESRD patients. Cardiovascular disease (CVD) and hemodialysis (HD) access-related infections remain the commonest causes of death in ESRD patients. A paradigm shift in the concept of overall care of patients is needed. This includes (but is not limited to) implementing good clinical practice guidelines, careful management of comorbid conditions, and making the best use of available technology.


Hemodialysis Adequacy


From a clinical perspective, ‘adequate’ HD should be considered to be the dialysis ‘dose’ at which the patient can lead a life as near to normal as possible in terms of physical and mental wellbeing.2


Perhaps, the best


definition is provided by Twardowski, who emphasizes the importance of ‘individualizing dialysis prescription’.3


Historical Perspective


The syndrome of ‘uremia’ (urine in blood) was first described by Prevot and Dumas in nephrectomized dogs in 1821.4


Bostock in 1826 and


Christison in 1829 subsequently demonstrated elevated blood urea concentrations in patients with renal failure, and urea was thus considered to be a ‘uremic toxin.’4


However, to date the evidence of


direct toxicity of urea remains scant. In the 1960s, Babb et al. observed that symptoms of peripheral neuropathy improved on peritoneal dialysis


© TOUCH BRIEFINGS 2010


Since solute removal is the major goal of dialysis, a measure of quantification for this purpose needs to be defined. Dialysis is a first-order


65


Diffusive removal is the result of random Brownian movement of solutes and is dependent on several variables derived from Fick’s law. HD works on the principle of diffusion, which is governed by the equation:


J = –DA (dc/dx) = –DA ∆c/∆x


The equation states that flux (J) of a solute over a short distance (∆x) is proportional to concentration difference (∆c) and area of diffusion front (A), D being the constant of proportionality. In clinical practice, dialyzer distance and surface area remain constant and thus flux is directly proportional to concentration gradient.


(PD), but not on HD. This was attributed to failure of HD to effectively remove higher molecular weight solutes, leading to the ‘middle molecule’ hypothesis. There is now accumulating evidence that there is a host of uremic toxins (other than urea) that have biologic and clinical effects in patients with renal failure.5,6


Understanding Clearance of Uremic Toxins Small solutes (<500Da) are effectively removed by diffusion. On the other hand, larger solutes are better removed by convective removal. Ultrafiltration (UF) of plasma water causes ‘solvent drag’ that leads to convective removal of solutes. Convective removal is independent of molecular size below the pore size cut-off of the membrane.


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88  |  Page 89  |  Page 90  |  Page 91  |  Page 92  |  Page 93  |  Page 94  |  Page 95  |  Page 96  |  Page 97  |  Page 98  |  Page 99  |  Page 100