Quantitation and adequacy Troubleshooting on haemodialysis
Kt/V and URR calculations Dialysis-related critical incidents
Routine monitoring Non-adherence
Medications (local patients)  

Quantitation and adequacy

Measurements of small molecule clearance have become an accepted way of assessing the adequacy of haemodialysis, because a correlation with mortality has been shown in large studies. It is a Renal Association standard that adequacy is checked monthly on all chronic haemodialysis patients.

Kt/V for urea* is the most widely accepted of these measurements, although a simple surrogate for this, urea reduction ratio (URR), is more readily measured and is also widely used. There is a calculator for Kt/V in Proton.

* K is a dialyser-specific figure for rate of urea clearance on an individual dialyser, at a given blood flow and dialysate flow. t is duration of dialysis. V is the volume of distribution of urea in a patient. 

Urea reduction ratio method

In the RIE we check Urea Reduction Ratio (URR), calculated as:

URR = 100 x [1 - Post(Urea)/Pre(Urea)]

The Edinburgh unit participates in a multicentre audit with comparison of URR results between all units in Scotland. This is the protocol approved by the Scottish Renal Association:

Only these bloods should be marked PRE (001) and POST (002) and are done by staff in the dialysis Units on a monthly basis.

Bloods taken without this stop flow will overestimate urea clearance on dialysis. Hence, while it may be appropriate to take bloods pre-dialysis on eg. in-patients to save patients venepuncure, and it is often necessary to know post dialysis potassium in out-patients who have not for whatever reason, completed their dialysis prescription, mark these bloods with the time they are taken, not pre/post or the 001/002 codes. This is very important as failure to do so causes problems with download of data to the Registry.

Problems with Kt/V & URR

Kt/V versus URR

Calculations based on URR alone underestimate Kt/V because no account is taken of the consequences of ultrafiltration.  This removes urea, but is ‘invisible’ by URR monitoring alone.

Table: correlation of URR to Kt/V corrected for ultrafiltration (NKF K/DOQI Guideline 2000). Calculated from single-pool, variable volume model with a body weight of 67.3kg, V of 35L, and NPCR of 1.0. Wt/BWt is the ultrafiltration volume/post dialysis weight x 100

 

URR Values at Kt/V

DWt/BWt

%

0.8

0.9

1.0

1.1

1.2

1.3

1.4

1.5

0

53

57

61

65

68

71

74

76

1

52

57

61

64

68

71

73

76

2

50

55

59

63

66

69

72

75

3

49

54

58

62

65

68

71

74

4

48

53

57

61

64

67

70

73

5

47

51

56

60

63

67

70

72

6

46

50

55

59

62

66

69

71

7

44

49

53

58

61

65

68

71

8

43

48

52

57

60

64

67

70

9

42

47

51

56

59

63

66

69

10

41

46

50

54

58

62

65

68

Prescribed Dialysis:

Dialysis should be prescribed on an individual basisThe variables influencing the amount of dialysis required are

The variables in the prescription that will improve dialysis adequacy are:

To prescribe adequate dialysis, please consult the following chart for a guide. Hours required to achieve Kt/V>1.3

MEN

FX8

 

 

 

FX10
FX60

 

 

 

 

Qb 250

Qb 300

Qb 350

Qb 400

Qb 250

Qb 300

Qb 350

Qb 400

40kg

3

3

3

3

3

3

3

3

50kg

3

3

3

3

3

3

3

3

60kg

3.75

3.25

3

3

3.5

3.25

3

3

70kg

4.25

3.75

3.5

3.25

4.25

3.75

3.25

3

80kg

4.75

4.25

4

3.5

4.75

4.25

3.75

3.5

90kg

5.5

4.75

4.5

4

5.25

4.75

4.25

4

100kg

6

5.5

5

4.5

6

5.25

4.75

4.25

110kg

6.5

6

5.25

5

6.5

5.75

5.25

4.75

120kg

7.25

6.5

5.75

5.25

7

6.25

5.75

5.25

 

 

 

 

 

 

 

 

 

WOMEN

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

40kg

3

3

3

3

3

3

3

3

50kg

3

3

3

3

3

3

3

3

60kg

3.5

3

3

3

3.5

3

3

3

70kg

4

3.5

3.25

3

3.75

3.5

3

3

80kg

4.5

4

3.5

3.25

4.35

4

3.5

3.25

90kg

5

4.5

4

3.75

5

4.25

4

3.5

100kg

5.5

5

4.5

4

5.5

4.75

4.25

4

110kg

6

5.5

5

4.5

6

5.35

4.75

4.25

120kg

6.5

6

5..25

5

6.5

5.75

5.25

4.75


FX8 : K= 0.51Qb + 93 t = dialysis time (min) FX10/60 : K= 0.55Qb + 87.3

V = 0.6 x dry wt (men), (x 0.55 women) FX80 : K= 0.8Qb + 38

When prescribed vs delivered dialysis differ:

If the prescribed vs delivered dialysis is very different, consider:

Routine monitoring of haemodialysis patients

This section describes the Edinburgh protocol.

Pre- and post-dialysis U & E, Creat monthly
LFTs, Ca, Alb, PD4 monthly
FBC monthly (fortnighly in RIE or if recent change in EPO dose
Iron Studies 2 monthly
PTH 2 monthly
Lipids annually, more often if high
HbA1c in diabetics 2 monthly
HepBsAg, HepC Ab 3 monthly
HIV Ab 12 montly
Aluminium 3 monthly
Cytotoxic antibodies (if on transplant list) monthly

 
Patients on HDF have in addition:

Trace metal & micronutrient screen, b2 microglobulin, B12 & folate
3 monthly

 
Adequacy targets:

For thrice weekly haemodialysis, the MINIMUM targets for patients with no residual renal function (SRA, RA, DOQI) are:

Kt/V >1.2 orURR >65% for all patients on chronic haemodialysis

To achieve this, the population mean needs to be Kt/V=1.3 or URR~70%

Higher values may be beneficial – and the unit average needs to be appreciably higher than these minima. Up to a Kt/V of 1.5-1.7 may be ‘good’, as long as not due to low V (weight).

Be aware that proton corrects URR to 2 significant places. Thus 65% can be 64.5-65.4% - While the target is arbitrary, it is based on survival data and 64.5 is not adequate dialysis

Other targets for monitoring (Renal Association – Guidelines March 2007)

K

3.5-6.5 mmol/l

PO4

1.1-1.8 mmol/l

Ca (corrected)

normal range

Ca x PO4 product

<4.8 mmol2/l2

PTH

130-260 (x2–x4 upper limit normal

Hb

>105-125g/dl (aim for 110g/dl)

Ferritin

100-800

Transferrin saturations

>20%

Aluminium

<2.2mmol/l

Bicarbonate

20-26mmol/l

Cholesterol

<5mmol/l

HbA1c

<7%

Pre-dialysis BP*

<140/90 mmHg

Post-dialysis BP*

<130/80 mmHg

* local not Renal Assoc target

Medications

Patients dialysing at the RIE are reviewed in a multidisciplinary team meeting approximately every 8 weeks.

Troubleshooting on haemodialysis

Hypotension

Usually occurs for one of three broad reasons:

Acute hypotension is usually managed by saline infusion, reducing weight loss; if out of character consider cardiac problems (rhythm, ischaemia). Management for recurrent hypotension is something like:

Cramps

Muscle cramps are very common during dialysis and can be of sufficient severity that they result in termination of the procedure. Their cause is unclear but the majority occur towards theend of the procedure after a significant volume of fluid has been removed. Their etiology is postulated to involve volume depletion and tissue hypoxia. They are associated with large requiremtns for fluid removal.

Pyrexia

Pyrexia in haemodialysis patients is usually related to the use of semi-permanent tunnelled access and most commonly due to Gram positive sepsis. It is common for dialysis to precipitate pyrexia in these circumstances. The exit site and tunnel should be checked for discharge, tenderness or erythema, but is commonly not abnormal.

All patients with ESRF are relatively immunosuppressed. 'Typical' bacterial infections of all types seem to be more common, and infection is the second most common cause of death in dialysis patients. Tuberculosis is possibly as common in haemodialysis patients as it is in patients immunosuppressed after receiving a renal transplant.

Non-functioning access

This is described in the section on Vascular Access

Dialysis-related critical incidents

The most serious acute events include air embolism, line disconnection leading to haemorrhage, acute haemolysis or toxicity related to line kinking or dialysis contamination, and acute allergic reactions to dialysers or sterilants (e.g., the 'first-use' syndrome attributed to antibody formation to ethylene oxide). If any such crisis occurs and the explanation is not entirely clear, in addition to all the necessary supportive measures:

The MHRA page on dialysis has alerts and information on haemodialysis and peritoneal dialysis equipment. In Scotland, report incidents via this dialysis incident-reporting link for Scotland (at SHOW; only works from inside NHSnet).

Non-adherence

Non-adherence to dialysis hours, dietary and fluid restrictions, etc are associated with increased mortality. These effects are probably indirectly associated as well as direct effects, but they are important and should be pointed out to patients who struggle to comply.  Download  warning leaflet from the foot of this page Patient information leaflet about non-adherence (pdf file, 1 page).

Further info

Calculating Kt/V - www.kt-v.net is a useful online tool from Asher Schachter of the Boston Children's Hospital. 

 

Acknowledgements:   Jane Goddard, Mariana Dimova and Neil Turner were the main authors for this page. The last modified date is shown in the footer.

 

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