Pediatric CRRT:Ultrafiltration Control

William E. Smoyer, M.D.

Pediatric Nephrology

University of Michigan

Introduction

• Ultrafiltration control not a widely accepted concern for CRRTOften not regulated in adult ICUsNo reports of significant volume imbalances

• Industry standards for pump error - 5-10%

• Few reports on CRRT pump accuracy (in vitro) 1,2

• Anecdotal reports of severe unanticipated volume depletion in several small children on CRRT

1 Jenkins R et al. ASAIO J. 38:808, 1992

2 Roberts M et al. Int J Artif Organs. 15:99, 1992

CRRT Pump Accuracy Study

• Hypothesis: Unanticipated fluid losses with CVVHD are clinically significant and result from variable pressure loads on the pumps

• Study Design:1) To prospectively analyze the accuracy of available IV

pumps during CRRT in vivo 2) To prospectively analyze the effects of blood flow,

total dialysate (D) + ultrafiltrate (UF) flow, and net UF flow rates on pump pressures in vitro

Methods

• Patients4 infants and children requiring CRRT (CVVHD)

• CRRT CircuitHemofilters:

Renal Systems; Renaflo II HF 400 (SA 0.30 m2) Hospal; Multiflow - 60 (SA 0.60 m2) Minntech; Minifilter Plus (SA 0.07 m2)

Blood Flow: 4 cc/kg/min (Gambro AK 10) IV Pumps:

Medex Trilogy / Alaris Gemini / Baxter Colleague 3

Methods

• In Vivo Data CollectionBags weighed on infant scale accurate to +0.5 ml (g)Sequential 1 hour measurements of:

“Set” vs. “Measured” dialysate inflow “Set” vs. “Measured” ultrafiltrate outflow

• In Vivo Data Analysis (1049 total pump-hours)Analysis of absolute hourly error for each pumpAnalysis of mean % error for each pumpComparison of each pump’s mean % error:

At variable pump flow rates During use for dialysate (inflow) vs. ultrafiltrate (outflow)

CRRT Pump Accuracy-Trilogy

0 100 200 250 300 400 500 600 700 800 900 1000-6

-5

-4

-3

-2

-1

0

1

2

3

Pump Flow Rate(ml/min)

Dialysate

Ultrafiltrate

Pump Accuracy over a Range of Flow Rates:Medex Trilogy

(n = 976 pump-hours)

CRRT Pump Accuracy-Gemini

0 100 200 250 300 400 500 600 700 800 900 1000-1

0

1

2

3

4

5

6

7

8Pump Flow Rate

(ml/min)Dialysate

Ultrafiltrate

Pump Accuracy over a Range of Flow Rates:Alaris Gemini

(n = 67 pump-hours)

CRRT Pump Accuracy-Colleague 3

0 100 200 250 300 400 500 600 700 800 900 1000-2

-1

0

1

2

3

4

5

6

7

Pump Flow Rate(ml/min)

Dialysate

Ultrafiltrate

Pump Accuracy over a Range of Flow Rates:Baxter Colleague 3

(n = 6 pump-hours)

CRRT Pump Accuracy-Combined

Trilogy Gemini Colleague 3 Combined-6

-5

-4

-3

-2

-1

0

1

2

3

4

5

6Dialysate

Ultrafiltrate

Cumulative

Mean Individual and Combined Pump Accuracyfor All Flow Rates

(n = 1049 pump-hours)

(Cumulative Error = Dialysate + Ultrafiltrate Error = Net Pump Error to Patient)

Results of In Vivo Studies

• Dialysate Pump Error (all pumps):Range: -6.8 +0.5% (-34.3 +4.7 ml/hr)Mean: -4.0%

• Ultrafiltrate Pump Error (all pumps):Range: -1.5 +7.4% (-13.7 +16.2 ml/hr)Mean: +0.9%

• Cumulative Pump Error (all pumps):Range: -7.9 +0.9% (-48.5 +9 ml/hr)Mean: -5.2%

Effect of Blood Flow on CRRT Pump Pressures-Trilogy

0

25

50

75

100

125

0 100 200 300

Blood Flow Rate(ml/min)

Dialysate Pre-Pump

Dialysate Post-Pump

UF Pre-Pump

UF Post-Pump

Blood Flow Rate vs. Pump Pressure:Medex Trilogy

*

*

*

+

+

+

(* = P < 0.05 vs. Blood Flow Rate 100)(+ = P < 0.05 vs. Blood Flow Rate 100)

Effect of Blood Flow on CRRT Pump Pressures-Colleague 3

0

25

50

75

100

125

0 100 200 300

Blood Flow Rate(ml/min)

Dialysate Pre-Pump

Dialysate Post-Pump

UF Pre-Pump

UF Post-Pump

Blood Flow Rate vs. Pump Pressure:Baxter Colleague 3

**

*

++

+

(* = P <0.05 vs. Blood Flow Rate 100)(+ = P <0.05 vs. Blood Flow Rate 100)

Effect of Total Flow on CRRT Pump Pressures-Trilogy

0

20

40

60

80

100

0 200 400 600 800 1000 1200

Total Flow Rate(ml/min)

Dialysate Pre-Pump

Dialysate Post-Pump

UF Pre-Pump

UF Post-Pump

Total Dialysate + Ultrafiltrate Flow Ratevs. Pump Pressure: Medex Trilogy

**

**

(* = P < 0.05 vs. Total Flow Rate 0)(+ = P < 0.05 vs. Total Flow Rate 0)

+

Effect of Total Flow on CRRT Pump Pressures-Colleague 3

0

20

40

60

80

100

0 200 400 600 800 1000 1200

Total Flow Rate(ml/min)

Dialysate Pre-Pump

Dialysate Post-Pump

UF Pre-Pump

UF Post-Pump

Total Dialysate + Ultrafiltrate Flow Ratevs. Pump Pressure: Baxter Colleague 3

**

**

(* = P < 0.05vs. Total Flow Rate 0)

* *

Effect of Net UF Flow on CRRT Pump Pressures-Trilogy

0

20

40

60

80

100

120

140

0 50 100 150 200 250 300 350

Net Flow Rate(ml/min)

Dialysate Pre-Pump

Dialysate Post-Pump

UF Pre-Pump

UF Post-Pump

Net Ultrafiltrate Flow Ratevs. Pump Pressure: Medex Trilogy

****

(* = P < 0.05vs. Net Flow Rate 0)

* *

* **

Effect of Net UF Flow on CRRT Pump Pressures-Colleague 3

0

20

40

60

80

100

120

140

0 50 100 150 200 250 300 350

Net Flow Rate(ml/min)

Dialysate Pre-Pump

Dialysate Post-Pump

UF Pre-Pump

UF Post-Pump

Net Ultrafiltrate Flow Ratevs. Pump Pressure: Baxter Colleague 3

(* = P < 0.05 vs. Net Flow Rate 0)

* *

Results of In Vitro Studies

• Direct correlation between blood flow rate and:D Post-Pump Pressures (80% increase)UF Pre-Pump Pressures (52% increase)

• Correlations with total D + UF flow rate:Direct - UF Post-Pump Pressures (0-15 mm Hg) Inverse - D Pre-Pump Pressures (75-69 mm Hg)

• Correlations with net UF flow rate:Direct - UF Post-Pump Pressures (14-21 mm Hg) Inverse - D Post-Pump Pressures (68-45 mm Hg) Inverse - UF Pre-Pump Pressures (93-71 mm Hg)

Summary

• Pump accuracy variable among available IV pumps for CRRTAll still within industry standards at all flow rates

• All 3 pumps consistently resulted in underinfusion of fluid when used for dialysate (inflow)

• 2 of 3 pumps consistently resulted in excess fluid removal when used for ultrafiltrate (outflow)

• Pump errors are generally additive and result in unanticipated fluid losses (x = -5.2%)

Summary

• Unanticipated fluid losses during CRRT with available IV pumps are clinically significant (>1000 ml/24 hr)

• Clinically relevant changes in blood flow, total dialysate + ultrafiltrate, and net ultrafiltrate flow rates do result in significant alterations in IV pump pressure loads

• Impact of IV pump pressure load changes on pump performance currently being analyzed