Accuracy of CVVH on ECMO : A comparison of IV pump versus Braun Diapact driven systems

Matthew L. Paden, MDDivision of Pediatric Critical Care

Emory UniversityChildren’s Healthcare of Atlanta at Egleston

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The Clinical Problem

Multiple ECMO/CVVH patients who are 10+ liters positive on paper, yet are clinically dehydrated

Hypothesis : Both IV pump and Braun Diapact driven CVVH systems when used with ECMO have error rates greater than 5% / hour.

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Methods for CRRT on ECMO

Commercially available CRRT machines• B Braun Diapact• Edwards Aquarius• Fresenius• Gambro

Prisma/Prismaflex

Advantage – Standardized equipment, “built for the purpose”

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Methods for CRRT on ECMO

IV Pump Driven• Described by Weber, et al 1998• IV pumps used to create ultrafiltrate and

deliver replacement fluid• Ultrafiltrate is measured using a

urometer Advantage – low cost, no additional training

for ECMO specialists, less extracorporeal blood volume

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The Problem

Inaccuracy has been described in CRRT in patients not on ECMO

The pumps are the problem• PCRRT 2000 –

7% extra ultrafiltrate removed 2% less replacement fluid delivered

• ASAIO 1992 – Up to 12.5% error rate Error correlates with pressure drop

across membrane and pump type

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Alaris Pump Accuracy

Sucosky et al. Awaiting publication. 2008

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Methods

Two identical saline primed ECMO circuits• Stockert S3, ½ inch drain, 3/8 inch return• 4.5 m2 Medtronic oxygenator• PAN 6 hemofilter

CVVH prescribed : IV pump vs. Diapact• Net even fluid balance• Varying ultrafiltration rates (0.5 – 2 L /

hour) Hourly weights of UF/Replacement bags,

circuit pressures

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Results

48 hourly measurements• 26 hours Alaris• 22 hours Diapact

No correlation between error rate and• Prescribed ultrafiltration rate• ECMO flow rate• CVVH blood flow rate

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Results - Alaris

Created a median 0.8% less ultrafiltrate per hour than prescribed (+7% to -12%)

Delivered a median of 4.3% less replacement fluid per hour than prescribed (+3% to -25%)

NET 3.5% of prescribed UF per hour dehydration to patient

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Examples with Alaris

4 kg neonate on ECMO with 100 ml/hour prescribed UF rate and even fluid balance• 84 ml (21 ml/kg) fluid negative per day

10 kg child on ECMO with 300 ml/hour prescribed UF rate and even fluid balance• 252 ml (25 ml/kg) fluid negative per day

45 kg child on ECMO with 2000 ml/hour prescribed UF rate and even fluid balance• 1.68 L (37 ml/kg) fluid negative per day

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Results - Diapact

Created a median 1% more ultrafiltrate per hour than prescribed (+6% to -8%)

Delivered a median of 1% more replacement fluid per hour than prescribed (+10% to -7%)

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Examples Braun

Accurate when looking at medians over time

Hourly variation could be important in a hemodynamically unstable patient

Hourly Fluid Balance

-5

35

10

10

35

-40

-5

0

-10

-30

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Conclusions

In this in vitro CVVH/ECMO model• Both the Alaris and Diapact methods had

error rates that could be clinically significant

• Careful physical assessment of the patient’s volume status is necessary

Further work is needed to develop more a accurate fluid management system for CRRT on ECMO