Continuous Renal Replacement

Therapy (CRRT): Fluid balance

and composition

Rinaldo Bellomo The University of Melbourne

Melbourne Australia

The risks of

fluid

overload

Positive fluid balance looks bad!

Why we might actually need to remove fluid

• Sustained oliguria leads to fluid overload due to obligatory fluid intake in ICU

• Fluid, acid-base, potassium management is much easier if urine output is maintained

• Fluid overload is a real problem

• Let me show you.

The “FACTTs” • NEJM 2006; 354: 1-12

• Comparison of two fluid-management strategies in acute lung injury

• NB: Pneumonia + sepsis >80% of patients

• 503 = conservative strategy

• 497 = liberal strategy

Liberal vs. conservative fluid use

0

2

4

6

8

10

12

14

16

MV-free

days

ICU-free

days

Liberal

Conservative

P<0.001

NB: need for RRT 2.8 vs. 1.9% (p=0.06) Mortality 28.4 vs. 25.5%. All in favour of “dry”

ALL given

Loop diuretics !!

Post-hoc analysis Clin J Am Soc Nephrol. 2011 May;6(5):966-73.

• Aim: explore association b/w FB, diuretics and mortality in AKI patients from FACTT

• 306 of 1000 patients developed AKI in first 2 days

• Post AKI Fluid Balance was significantly associated with mortality…higher frusemide doses had a protective effect which was no longer significant after correction for fluid balance.

• Conclusion: Post AKI diuretic therapy was associated with better 60-days survival – this appeared mediated by more negative fluid balance

Positive fluid balance is bad in AKI

Cohort of 370 patients from Austin Hospital ICU

101

109 109,5

114,5

109,5 110 110 110 108

112,5

119 117

121 122

111 112,5 112 112 115

120

110 109

100 101

0

20

40

60

80

100

120

140

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Ult

rafi

ltra

tio

n(m

l)

Hours

Hourly Net Ultrafiltration

0

20

40

60

80

100

120

140

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Flu

id In

take

(m

l)

Hours

Hourly Fluid Intake and Output During CRRT

Median intake Median output

Fluid composition

• Bicarbonate-buffered fluid is the standard composition

• However, citrate CRRT is becoming dominant and commercial products use a combination of citrate and bicarbonate

• If citrate is used appropriate adjustments need t be made to ensure a near physiologic buffer concentration (25-35 mEq/L)

The data are clear!

P=0.0037

For all circuits: HR for clotting 2.03 using frailty model

Conclusions

• Avoidance of fluid overload is important during RRT

• Higher net UF aimed at achieving near dry weight after the initial resuscitation phase is desirable

• Very high net UF rates may be a marker of illness severity and may be undesirable as well

• Much more work is needed in the field of volume control during RRT in ICU

• Fluid composition is moving toward citrate. If citrate CRRT is not applied bicarbonate is the standard