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

1. Accuracy of CVVH on ECMO : A comparison of IV pump versus Braun Diapact driven systems Matthew L. Paden, MD Division of Pediatric Critical Care Emory University Children’s Healthcare of Atlanta at Egleston

2. 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.

3. 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”

4. 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

7. 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

8. Alaris Pump Accuracy Sucosky et al. Awaiting publication. 2008

9. 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

10. 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

11. 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

12. 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

13. 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%)

14. Examples Braun • Accurate when looking at medians over time • Hourly variation could be important in a hemodynamically unstable patient

15. 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