• This applies to conventional intermittent 3 times a week hemodialysis
  • Per KDOQI 2006 guidelines:  For patients with minimal residual renal function (<2ml/min per 1.73m²)
    • Minimally adequate dose should be a spKt/V of 1.2
    • Target recommended dose should be a spKt/V of 1.4 (or eKT/V of 1.2)

• There is a lack of randomized studies to support the minimum dialysis dose of spKt/V ≥1.2.
• However, retrospective studies suggest that a Kt/V <1.0 is associated with poor outcomes and that a Kt/V ≥1.2 is associated with better survival¹²³.
• The HEMO study⁴ showed that targeting a spKt/V higher than 1.4 did not improve survival or reduce hospitalization rates over 2.8 years.

Sources:

1. Owen WF Jr, Lew NL, Liu Y, et al. The urea reduction ratio and serum albumin concentration as predictors of mortality in patients undergoing hemodialysis. N Engl J Med. 1993;329(14):1001.
2. Gotch FA, Levin NW, Port FK et al. Clinical outcome relative to the dose of dialysis is not what you think: the fallacy of the mean. Am J Kidney Dis. 1997;30(1):1.
3. Held PJ, Port FK, Wolfe RA et al. The dose of hemodialysis and patient mortality. Kidney Int. 1996;50(2):550.
4. Eknoyan G, Beck, GJ Cheung AK, et al. Effect of dialysis dose and membrane flux in maintenance hemodialysis. N Engl J Med 2002; 347:2010. Hemodialysis study (HEMO)

As you go through this section of the module consider the following scenario:

67 year old African American male with history of diabetes, hypertension, coronary artery disease, and end stage renal disease secondary to diabetic nephropathy is on hemodialysis three times a week for 4 hours via a left arm brachiocephalic AV fistula. You are the rounding nephrologist in the dialysis unit and a concerned nurse reports that the patient’s most recent Kt/V is 1.0 down from previous levels of 1.4-1.6.

1. What is Kt/Vurea?
2. How do we measure Kt/V?
3. What is the goal Kt/V?
4. Why do we care about Kt/V?
5. Troubleshooting a drop in Kt/V
6. What are the limitations of Kt/V?
7. Playground! Play around with variations of Qb (access blood flow rate), Qd (dialysate flow rate) and KoA to see  how it impacts K and Kt/V
   1. Playground Debrief

When Kt/V drops:

• 40% of the cases occur due to decreased dialysis time or inadequate dialyzer blood flow (Qb)
• 25% of cases are due to significant access recirculation

Troubleshooting:

• Repeat measurement to confirm the drop using standardized measurement technique as described in the video “How to measure Kt/V in the HD unit”
• Confirm accuracy of post BUN measurement
• Confirm adequate Qb and time on dialysis
• Check access integrity
• Optimize Qb and Treatment time, resolve access issues
• Use a higher efficiency dialyzer (higher KoA)
• Can increase dialysate flow (Qd) although gain above 800ml/min is minimal

• Kt/V overestimates dialysis adequacy in thin, malnourished patients and elderly females due to sarcopenia and a low ‘V’. This may lead to under-dosing of dialysis. Kt corrected for body surface area may be a more accurate measure of dialysis dose in these patients.
• There is a high index of error related to inaccurate post-dialysis BUN measurement.
• Single treatment may not represent other treatments ( missed or shortened)
• spKt/V or eKt/V is not applicable to daily or nocturnal dialysis. It is useful only for conventional 3 times a week intermittent hemodialysis.
• Kt/V is a marker only of urea clearance and not of other toxic/uremic solutes that exist.
• Other uremic toxins such as phosphate, β2 microglobulin, guanidino compounds etc. do not follow the same hemodialysis kinetics as urea and therefore their clearances are not accurately reflected by Kt/Vurea.¹
• A high Kt/V(>1.4) has not been shown to predict better survival in any randomized controlled studies (e.g. HEMO study²).This implies that there are other determinants of poor survival in hemodialysis patients besides urea clearance and that despite a high dialysis urea clearance (Kt/V), patients may retain other toxic solutes that ultimately are equally or more important than urea in influencing prognosis on dialysis.³
• Despite these controversies surrounding KT/Vurea, it remains the most frequently used parameter for determining dialysis adequacy and its routine monitoring may help to identify problems of dialysis delivery such as access recirculation etc.

Sources:

1. Comparing the urea reduction ratio and the urea product as outcome-based measures of hemodialysis dose. AU Li Z, Lew NL, Lazarus JM, Lowrie EG SOAm J Kidney Dis. 2000;35(4):598.
2. Eknoyan G, Beck, GJ Cheung AK, et al. Effect of dialysis dose and membrane flux in maintenance hemodialysis. N Engl J Med 2002; 347:2010.
3. Meyer TW,Sirich TL,Fong KD et al. Kt/Vurea and non urea small solute levels in the hemodialysis study. JASN 2016;27:3469

• Urea is considered a surrogate to other small molecular weight uremic toxins and is easy to measure in the blood pre and post hemodialysis.
• Although its use has limitations, it is an easily measured and useful marker of hemodialysis adequacy.
• Kt/Vurea has helped standardize dialysis dosage based on urea clearance. It provides a tool to avoid grossly inadequate dialysis.
• Its routine monitoring may help to identify problems of dialysis delivery such as access recirculation. 
• Urea reduction ratio (URR= 1-postdialysis BUN/predialysis BUN) is a less optimal measure of dialysis adequacy as it does not account for ultrafiltration during dialysis and assumes that V is constant during dialysis.

Daugirdas mathematical formula to calculate:
Kt/V  = -ln (R – 0.03) + [(4 – 3.5R) x (UF ÷ W)]

Where…
R= post HD BUN/preHD BUN
UF= UF volume in L
W=  post dialysis weight in kg

Online calculators and normograms are available to calculate Kt/V using formula above.

The quick and dirty method:

• If the dialyzer’s clearance (K) is known (based on the packet insert provide by the manufacturer at a Qb of 400ml/min) and is 250 ml/min and the dialysis session time is 240 minutes (4 hours)
  • then Kt (dialysis dose)= 250 x 240 = 60,000ml or 60 liters
• If the patient weighs 70kg. His TBW is 60% of 70kg
  • then V = 70 kg multiplied by .60 = 42 liters
• So the ratio – K multiplied by t to V, or Kt/V – compares the amount of water that passes through the dialyzer and is cleared of urea to the amount of water in the patient’s body.
  • KT/V for this patient will be= 60/42 = 1.42

Caveat: If this same patient has 3 kg of  edema fluid (EDW of 70kg)  then V = 60% (70kg)+ 100%(3kg)= 45L and not 42L. This is because edema fluid adds to the TBW in its entirety as urea distributes evenly across body water.