HEMODIALYSIS ADEQUACY

1. HEMODIALYSIS ADEQUACY

2. Definition
• Dialysis adequacy is defined as the minimum
amount of urea clearance and nutritional intake
that prevents adverse outcomes.
• Adequacy of dialysis refers to how well we
remove toxins and waste products from the
patient’s blood, and has a major impact on
their well-being

3. Aspects of dialysis adequacy
• Clinical
Control of anaemia, acidosis
Control of bone disease.
Control of BP
Relief of uremic symptoms
Quality of life and life expectancy

4. • Measurement
• Small solute clearance (urea kinetic modelling
(UKM)
• Kt/V
• urea reduction ratio (URR)).

5. How do we know if a Patient is
Adequately Dialyzed ?
• The National Cooperative Dialysis Study (NCDS)
established urea kinetic modeling (UKM) as the
accepted method of measuring small solute
clearance.

6. Moleular Weight of 60
a marker for small MW uremic toxins
Urea removal < ---> other small toxin
removal
WHY UREA ?
The clearance of urea has been selected as the
basis for all the calculations of dialysis adequacy

7. Urea Clearance Factor
• The urea clearance coefficient of the dialyzer
• The pre and post treatment blood urea
• The treatment time,
• The total body water,
• The UF,
• Residual renal function and
• The interdialytic urea generation rate.

8. UKM
• When calculations of dialysis adequacy use
both urea clearance and patient nutritional
status (i.e., urea generation rate), this is called
UKM.
• It takes into account residual renal function,
predicted dialyser clearance, blood and
dialysate flow, time on dialysis and fluid
removal.

10. Measures of dialysis adequacy
• URR
• spKt/V = single pool
• eqKt/V = equilibrated (Double pool)
• Std Kt/V = weekly standard

11. URR
• It is calculated as follows:
[(Pre-dialysis urea – post-dialysis urea)/Pre-
dialysis urea] × 100.
• Simple
• Prediction of mortality
Limitation:
• Does not account for the contribution of UF to
dialysis dose

12. Kt/V = fractional urea clearance
K = dialyzer clearance (ml/min or L/hr)
t = time (min or hr)
V = distribution volume of urea (ml or L)
K x t = L/hr x hr = LITERS
V = LITERS
Kt/V = LITERS/LITERS = ratio
What is Kt/V ?

13. • K stands for the dialyzer clearance, the rate at
which blood passes through the dialyzer,
expressed in milliliters per minute (mL/min)
• Kt, the top part of the fraction, is clearance
multiplied by time, representing the volume
of fluid completely cleared of urea during a
single treatment

15. spKt/V = single pool
eqKt/V = equilibrated (Double pool)
Std Kt/V = weekly standard
Kt/V

16. • A urea Kt/V value <0.8 was found to be
associated with a high likelihood of morbidity
and/or treatment failure, while a Kt/V >1.0
was associated with a good outcome
• Guidelines have recommended a minimum
Kt/V value of at least 1.2 for hemodialysis
patients being dialyzed three times per week

17. spKt/V
• The single pool Kt/V assumes that, at the end
of dialysis, the concentrations of intracellular
and extracellular Ur are equal
• (Upre, urea pre-dialysis; Upost, urea post-dialysis; UFvol,
volume removed on dialysis)

18. Single-Pool vs Double-Pool
Single-pool
• Does not account for urea transfer between fluid
compartments
• With  dialyzer clearance, urea removed from
extracellular compartment can exceed transfer
from intracellular compartment
• Urea rebound (30-60 min)
• So Dialysis dose will be overestimated if this urea
pool is large.

21. Equilibrated Kt/V
• eKt/v is 0.2 units less than single-pool kt/v, but
it can be as great 0.6 unit less.
• urea rebound is nearly complete in 15 minutes
after hemodialysis but may require up to 50-
60 minutes

30. Contd.
• The degree of rebound is high in small patient
• eKt/V= spKt/V - 0.6 x (spKt/V) / t + 0.03 (for
arterial access)
• eKt/V= spKt/V - 0.47 x (spKt/V) / t + 0.02 (for
venous access)

31. STANDARD Kt/V UREA.
The so-called “standard” Kt/V urea grew out of
two desires:
(1) to come up with a measure of hemodialysis
adequacy that was not dependent on number of
treatments per week and
(2) to have a measure where the minimum dose
for hemodialysis would be similar to the
minimum dose for peritoneal dialysis.

32. Minimum dialysis dose
• URR >65%
• SpKt/V > 1.2
• eKt/V > 1.2
• StdKt/V 2.0

33. 1. To recommend a target single pool Kt/V (spKt/V) of 1.4
per hemodialysis session for patients treated thrice
weekly, with a minimum delivered spKt/V of 1.2.
2. In patients with significant residual native kidney
function (Kr), the dose of hemodialysis may be
reduced provided Kr is measured periodically.
3. For hemodialysis schedules other than thrice weekly, a
target standard Kt/V of 2.3 volumes per week with a
minimum delivered dose of 2.1 using a method of
calculation that includes the contributions of ultrafiltration
and residual kidney function.
Measurement of Dialysis: Urea Kinetics

34. Clearance of other molecules:
• ‘ Middle ’ molecule clearance thought to be
important to prevent the long-term complications
of dialysis.
• B2 microglobulin is the most used marker.
• Phosphate clearance is also important and
appears to correlate more with hours of dialysis
than rate of small molecule clearance.

35. Normalized protein catabolic rate (nPCR)
• A measure of Ur generation, which reflects
nutritional status. Ur generation will broadly
reflect protein intake.
• It is felt that patients require an nPCR
>1.0g/kg/day.
• nPCR of <0.8g/kg/day is associated with
higher mortality.

36. Nutrition
Targets:
• Serum albumin >35g/L.
• Normalized protein catabolic rate (nPCR)
>1.0g/kg/day.
• Acceptable anthropometric measures.

37. Residual function
• When HD is first commenced, residual renal
function may contribute greatly to the total
amount of solute clearance (Kru).
• This is usually calculated with a 24h urine
collection.
• Residual function tends to diminish quickly on
HD.

38. Ensuring adequacy
• Kt/V
a sp Kt/V >1.2 for patients dialysed x 3/week,
equating to a URR of ~65%.
• Residual renal function should always be taken
into account.

39. Causes of Inadequate Dialysis
• Improper dialysis prescription
• Inadequate blood flow
• Reduction in treatment time
• Dialyzer clotting, leaks
• Recirculation

40. How to improve clearance?
 Improve vascular access — if flows are poor
or if there is access recirculation, it will be hard
to improve clearances.
 Increase blood flow/larger needles .
 Increase dialyser size — modest impact.
 Increase dialysate flow.
 Increase dialysis time/frequency — major
benefit.
 Consider HDF.

41. Home Message
Dialysis can be considered adequate if it provides
 relief of uraemic symptoms and
 controls acidosis,
 Control of BP,
 Correction of anemia
 fluid & Electrolyte balance,
 feeling of physical and psychological well-
being

42. references
• KDOQI Hemodialysis Adequacy-Clinical
Practice Guideline Update 2015: What You
Need to Know by NKF
• Daugirdas dialysis book
• Questionnaire from journals