Download - Dialysis Adequacy (?)
EDWARD WELSHMARCH 31 2010
Dialysis Adequacy (?)
Disclaimer
Adequate
Equal to a requirement
Barely satisfactory
Acceptable
Would you be happy with “adequate” therapy ?
Outline
Basics of renal function
History and Trials
Formulae
Problems
Kidney Function
Maintain a steady state environmentContinuous function and adjustment of
metabolic parameters
FiltrationSecretionMetabolicSynthetic
Uremic Toxins
Many known , many more unknown
Small water soluble – ureaLarger water soluble –guanidinesPhosphatesProtein bound compounds- cresols , drugs
Middle molecules (MW>500 D)- greater than 20 compounds….AGE’s , B2M , PTH
Hemodialysis
Replaces filtration
Diffusive and convective losses
Intermittent and short duration – 12 hours vs 168
Cont’
Removes volume , electrolytes , water soluble wastes and ( slowly) middle molecules and P04
No metabolismNo secretionNo synthetic functionNo removal of protein bound wastes
Urea Kinetic Modeling
TAC , AUCKt/VURRPRUeKt/VSingle pool Kt/VDouble pool V
Area under the Curve
Weekly substance concentrations in routine HD
Time
Conc
entra
tion
History
? Quantity dialysis correlated with outcome
Initially used nerve conduction , bleeding times , EEG - all poorly standardized
Various toxins proposed/measured – middle molecules (B12 used as marker)
Urea shown not to have toxic effects
First Study
National Cooperative Dialysis Study (NCDS) published 1982
150 patients from 8 US centers4 groups - 4 ½ hours and high TAC (36) - 4 ½ hours and low TAC (18) - 3 ½ hours and high TAC - 3 ½ hours and low TAC 3 runs per week , no real diet
Outcome
Study stopped early – analysis revealed higher mortality in high TAC group
Seemed to validate urea as useful marker
Reanalysis data in 1985 – Gotch – led to UKM and Kt/V
Kt/V of 0.9 considered minimumHigh TAC , 3 ½ hour group received Kt/V of
0.4 !
Oops
Fixation on urea alone led to “high efficiency” dialysis with short runs mid 80’s to early 90’s in the US
Poor outcomes
Rest of world better outcomes – longer times
Tassin - 3 runs per week , 8 hours per run
HEMO Trial 2002
? Optimal dialysis dose1846 patients Standard vs high dialysis dose and low vs
high flux dialyzersStandard dose group - Kt/V = 1.25High dose group - Kt/V = 1.65
Hemo outcomes
Outcome
17% mortality rate per year40% due to cardiac events
NO difference between any groups !
Risk of Death vs URR or Alb
URR
Albumin
Kt/V
K= dialyzer clearance
t = time on dialysis
V = volume of patient body water
? Calculate KT/V
Need pre/post urea
Existing patient data
Treatment info
All done same day
Need computer program
Urea Reduction Ratio (URR)
(Pre Urea – Post Urea ) /Pre Urea
A single snapshot , easy to calculate
PRU = URR x 100%
Prescribed vs Actual
Prescribed - computerized estimation
Actual – real run….. access that day , blood flow rates , treatment
time
Timing
When to measure post urea ?Too soon – post too low
Single pool RecirculationCompartment dysequilibrium
Timing of Post Urea
Dialyzers
Urea removed in relation to dialyzer surface area
Larger surface area = greater removal urea
Appropriate heparin to prevent clotting
No reuse
Other factors
Actual time on run
Access type ? Recirculation
Blood flow and dialysate flow rates – real vs entered
Episodes hypotension…..
KDOQI guidelines 2006
Three runs a weekMinimum run time 3 hours
Kt?/V - target 1.4 with min 1.2URR -target 70% with min 65%
Kt/V is standard of practice
Netherlands Cooperative Study
Residual renal function (RRF)
Low Kt/V associated with mortality in anuric pts
Need to consider both dialysis and renal Kt/V
Excess interdialytic weight gain correlated with increase in mortality independent of Kt/V !
Conclusions
Urea kinetics useful , but is only one measure of adequacy
Other measures - Quality of life - Volume and BP control - Ca x Po4 - B2M…..
LOOK at the patient !
Questions ?