Elizabeth Lindley

A comparison of methods for determining urea distribution volume for routine use in on-line monitoring of haemodialysis adequacy

BACKGROUNDnThe availability of haemodialysis machines equipped with on-line clearance monitoring (OCM) allows frequent assessment of dialysis efficiency and adequacy without the need for blood samples. Accurate estimation of the urea distribution volume V is required for Kt/V calculated from OCM to be consistent with conventional blood sample-based methods.nnnMETHODSnTen stable HD patients were monitored monthly for 6 months. Time-averaged OCM clearance (K(OCM)) and pre- and post-dialysis blood samples were collected at each monitored session. The second generation Daugirdas formula was used to calculate the single-pool variable volume Kt/V, (Kt/V)(D). Values of V to allow comparison between OCM and blood-based Kt/V were determined from Watsons formula (V(Watson)), bioimpedance spectroscopy (V(BIS)), classical urea kinetic modelling (V(UKM_C)) and a simple computation of V (V(UKM_S)) from the blood-based Kt/V and K(OCM)t.nnnRESULTSnComparison of K(OCM)t/V with (Kt/V)(D) shows that using V(Watson) leads to significant systematic underestimation of dialysis dose. K(OCM)t/V(BIS) agrees with (Kt/V)(D) to within +/- 10%. K(OCM)t/V(UKM_S) is, by definition, identical to (Kt/V)(D) when initially calculated. However, if a historical value of V is used, agreement between K(OCM)t/V and (Kt/V)(D) over 6 months varies by 5% for V(BIS) and 10% for V(UKM_S).nnnCONCLUSIONSnWhen investigating the effect of different treatment strategies on dialysis efficiency, any estimate of V can be used provided it is constant, as K is the relevant parameter. When frequent supervision of actual dialysis dose is required, the greatest consistency between K(OCM)t/V and the reference, Kt/V(D), over time is achieved with V(BIS).

A randomized, controlled study of the consequences of hemodialysis membrane composition on erythropoietic response.

BACKGROUNDnMembrane biocompatibility has long been thought to be relevant to hemodialysis outcomes and, possibly, renal anemia.nnnMETHODSnWe performed a randomized, controlled, single-center study comparing the consequences on renal anemia of 2 dialyzers of equivalent performance, but different composition, during 7 months. Two hundred eleven patients of an unselected dialysis population of 235 patients gave informed consent to undergo random assignment to either group A (SF170E; modified cellulose triacetate/midflux membrane; Nipro, Osaka, Japan) or group B (HF80LS; polysulfone/high-flux membrane; Fresenius, Bad Homburg, Germany). Anemia management was identical in both treatment groups and followed strict clinical protocols managed by computer algorithms. Dialysis adequacy, hemoglobin (Hb) level, ferritin level, percentage of red blood cell hypochromicity, C-reactive protein (CRP) level, and intravenous iron and epoetin doses were monitored monthly.nnnRESULTSnOne hundred seventy-seven patients completed the 7-month study. Equilibrated Kt/V increased in both groups. Hb outcome improved overall, but did not differ between the 2 study groups. Epoetin dose was not significantly different after 7 months compared with baseline in either group. Hb level, epoetin dose, iron status, CRP level, dialysis Kt/V, and residual renal function did not differ between the 2 groups. A slight but significant negative correlation was identified between dialysis Kt/V and Hb level in the population as a whole (Spearmans correlation, -0.16; P = 0.04).nnnCONCLUSIONnNo significant epoetin-sparing effect was identified through the use of the high-flux polysulfone HF80LS membrane over the modified cellulose triacetate SF170E membrane. Although not a primary outcome for this study, there was a suggestion of benefit of improved Hb level, without increased need for epoetin, through increasing delivered dialysis dose.

A predictive algorithm for the management of anaemia in haemodialysis patients based on ESA pharmacodynamics: better results for less work

BACKGROUNDnMany anaemia management algorithms recommend changes to erythropoiesis-stimulating agent (ESA) doses based on frequent measurement of haemoglobin levels in keeping with the ESA datasheets. We designed a predictive anaemia algorithm based on ESA pharmacodynamics, which we hoped would improve compliance with haemoglobin targets and reduce workload.nnnMETHODSnA new algorithm was designed which predicted the 3-month steady-state haemoglobin concentration following a change in ESA dose and only recommended a change if it was outside the range 10.5-12.5 g/dL. Data were collected prospectively for 3 months prior and 15 months subsequent to implementing the algorithm.nnnRESULTSnA total of 214 prevalent dialysis patients were included in the audit. After 12 months, the haemoglobin concentration was 11.4 g/dL, near the midpoint of the target range, with a narrowing of the distribution (SD 1.46 to 1.25 g/dL, P < 0.0001). The proportion of patients with a haemoglobin level in the target range increased from 56% to 66% (P < 0.001) principally due to a reduction in the number of patients with high haemoglobin levels. There was no significant change in the ESA dose over the audit period. The number of prescription changes fell from 1/2.5 months to 1/6.1 months after 12 months (P < 0.001).nnnCONCLUSIONSnSwitching prevalent haemodialysis patients to a predictive anaemia management algorithm improved compliance with haemoglobin targets, reduced the number of patients with high haemoglobin levels and reduced the number of ESA dose changes required.

A randomized controlled trial evaluating the erythropoiesis stimulating agent sparing potential of a vitamin E-bonded polysulfone dialysis membrane

Background Vitamin E (VE) bonded polysulfone dialysis membranes have putative erythropoiesis stimulating agent (ESA)-sparing and anti-inflammatory properties based on data from a small number of studies. We sought to investigate this in a large, prospective 12-month randomized controlled trial. Methods Two-hundred and sixty prevalent haemodialysis (HD) patients were randomized to dialysis with VE-bonded polysulfone membranes or non-VE-bonded equivalents. All ESA-dosing was performed by means of a computer-based anaemia management decision support system. Monthly data were used to calculate the ESA resistance index (ERI) and blood tests were performed at baseline, 6 and 12 months for measurement of C-reactive protein (CRP) levels. Results Of the 260 patients, 123 were randomized to dialysis with the VE-membrane and 12-month data was available for 220 patients. At the study population level, no beneficial effect of the VE membranes on the ERI or CRP levels was observed. Post hoc analyses indicated that there was a significant fall in ERI for patients with the highest baseline ESA resistance dialysed with the VE (9.28 [7.70–12.5] versus 7.70 [5.34–12.7] IU/week/kg/g/dL Hb, P = 0.01) but not the control membranes (9.45 [7.62–12.3] versus 8.14 [4.44–15.6] IU/week/kg/g/dL Hb, P = 0.41); this was not attributable to changes in CRP levels. Conclusions Wholesale switching of all chronic HD patients to dialysis with VE-bonded polysulfone membranes appears not to be associated with improvements in ESA-responsiveness or CRP. These membranes may have utility in patients with heightened ESA resistance.

SHOULD DIALYSATE CALCIUM CONCENTRATION BE STANDARDISED OR INDIVIDUALISED

The 2003 K/DOQI bone metabolism guidelines recommend a standard dialysate calcium concentration of 1.25 mmol/l. Studies of calcium balance that take ultrafiltration, as well as changes in ionised calcium, into account show that patients lose calcium when treated with this dialysate Ca. Compensation for negative calcium balance will usually be required in patients with normal or high bone turnover, but may be impossible if the recommendations to restrict intake of calcium, and hold vitamin D therapy if serum phosphate is high, are followed. A literature review suggests that conversion to 1.25 mmol/l dialysate Ca is beneficial in selected, but not all, patients. Conversion to higher dialysate Ca levels has been shown to improve control of calcium, phosphate and PTH, again in selected patients. Given the important role that dialysate calcium concentration plays in the management of renal bone disease, it should be prescribed on an individual basis like other medications.