Prescribed versus delivered dialysis: Importance of dialysis time
- Robert Hootkins, MD, PhD, FACP, FAHA, FASN
Robert Hootkins, MD, PhD, FACP, FAHA, FASN
- Clinical Associate Professor of Medicine
- University of Texas Southwestern
- William L Henrich, MD, MACP
William L Henrich, MD, MACP
- University of Texas Health Science Center at San Antonio
- Richard A Sherman, MD
Richard A Sherman, MD
- Professor of Medicine
- Rutgers - Robert Wood Johnson Medical School
Adequacy of hemodialysis is an important issue since it appears to be an important determinant of patient survival (see "Patient survival and maintenance dialysis"). One method of assessing the amount of dialysis prescribed is to assess urea removal normalized for a measure of body size, the Kt/V. This parameter can be estimated from the dialyzer urea clearance data supplied by the manufacturer (K), the duration of dialysis in minutes (t), and the patient's urea space (V) as derived from a standard height/weight nomogram.
A number of the major factors contributing to K are:
●The size of the dialysis membrane since larger surface area membranes can remove more urea per unit time.
●The blood flow rate to the dialyzer (Qb) since presenting new plasma with a high urea concentration maintains the favorable gradient for urea removal (figure 1).
●The dialysate flow rate (Qd) since delivering new fluid containing no urea also maintains the urea concentration gradient.
- Parker TF, Husni L. Delivering the prescribed dialysis. Semin Dial 1993; 6:13.
- Sargent JA. Shortfalls in the delivery of dialysis. Am J Kidney Dis 1990; 15:500.
- Hootkins R, Bourgeois B. The effect of ultrafiltration on dialysance. Mathematical theory and experimental verification. ASAIO Trans 1991; 37:M375.
- Depner TA. Assessing adequacy of hemodialysis: urea modeling. Kidney Int 1994; 45:1522.
- Sherman RA. Recirculation revisited. Semin Dial 1991; 4:221.
- Schneditz D, Kaufman AM, Polaschegg HD, et al. Cardiopulmonary recirculation during hemodialysis. Kidney Int 1992; 42:1450.
- Depner TA, Rizwan S, Cheer AY, et al. High venous urea concentrations in the opposite arm. A consequence of hemodialysis-induced compartment disequilibrium. ASAIO Trans 1991; 37:M141.
- Star RA, Hootkins R, Thompson JR, et al. Variability and stability of two pool urea mass transfer coefficient (abstract). J Am Soc Nephrol 1992; 3:395.
- Gabriel JP, Fellay G, Descombes E. Urea kinetic modeling: an in vitro and in vivo comparative study. Kidney Int 1994; 46:789.
- Schneditz D, Van Stone JC, Daugirdas JT. A regional blood circulation alternative to in-series two compartment urea kinetic modeling. ASAIO J 1993; 39:M573.
- Schneditz D, Daugirdas JT. Formal analytical solution to a regional blood flow and diffusion based urea kinetic model. ASAIO J 1994; 40:M667.
- Daugirdas JT, Schneditz D. Overestimation of hemodialysis dose depends on dialysis efficiency by regional blood flow but not by conventional two pool urea kinetic analysis. ASAIO J 1995; 41:M719.
- George TO, Priester-Coary A, Dunea G, et al. Cardiac output and urea kinetics in dialysis patients: evidence supporting the regional blood flow model. Kidney Int 1996; 50:1273.
- George TO, Prifster-Coary A, Dunea G, et al. Cardiac output and urea kinetics in dialysis patients: Evidence supporting the regional blood flow model and the concept of cardiopulmonary recirculation (abstract). Blood Purif 1997; 15:3.
- Smye SW, Hootkins RE, Will EJ. Solute clearance and tissue clearance times. Semin Dial 1998; 11:185.
- Cortez AJ, Paulson WD, Schwab SJ. Vascular access as a determinant of adequacy of dialysis. Semin Nephrol 2005; 25:96.
- Wei SS, Ellis PW, Magnusson MO, Paganini EP. Effect of heparin modeling on delivered hemodialysis therapy. Am J Kidney Dis 1994; 23:389.
- Coyne DW, Delmez J, Spence G, Windus DW. Impaired delivery of hemodialysis prescriptions: an analysis of causes and an approach to evaluation. J Am Soc Nephrol 1997; 8:1315.
- Clark WR, Leypoldt JK, Henderson LW, et al. Quantifying the effect of changes in the hemodialysis prescription on effective solute removal with a mathematical model. J Am Soc Nephrol 1999; 10:601.
- Rocco MV, Lockridge RS Jr, Beck GJ, et al. The effects of frequent nocturnal home hemodialysis: the Frequent Hemodialysis Network Nocturnal Trial. Kidney Int 2011; 80:1080.
- Depner T, Daugirdas J, Greene T, et al. Dialysis dose and the effect of gender and body size on outcome in the HEMO Study. Kidney Int 2004; 65:1386.
- HISTORICAL BACKGROUND
- DETERMINANTS OF DIALYTIC SOLUTE CLEARANCE
- DIMINISHED UREA CLEARANCE DUE TO THE PARALLEL NATURE OF HEMODIALYSIS
- Vascular access recirculation
- DIMINISHED UREA CLEARANCE DUE TO DIMINISHED EQUILIBRATION WITH INTRACELLULAR STORES
- Regional blood flow model
- OTHER LIMITING FACTORS
- Inaccurate manufacturer's specifications
- Inaccurate and decreased blood flow rates
- Reduced fiber bundle volume from clotting
- Inefficient dialysis
- Errors in measurement of blood urea nitrogen
- Residual urea clearance
- TOTAL BODY-EFFECTIVE CLEARANCE AND TIME ON DIALYSIS
- INFORMATION FOR PATIENTS