Design of a More Efficient Heat Exchanger for Inducing Hypothermia in Neonatal ECMO Cases

1. University of Pittsburgh Senior Design - BIOE 1161 April 13, 2004 Design of a More Efficient Heat Exchanger for Inducing Hypothermia in Neonatal ECMO Cases Adam Abdulally Erin Aghamehdi Kim Albrecht Rebecca Hrutkay

2. Background ECMO & Hypothermia Overview Re-design Audience Device Description Features & Benefits Project Objectives Spring 04 Future Project Management Design Alternatives Quality Systems Experimental Design SA calculations Technologies Competitive Analysis Testing Requirements Projected Methods Outline

3. ECMO Background • Provides temporary cardiac and/or pulmonary support for patients with potentially reversible cardiac and/or respiratory failure • ECMO Stats: • 8000 neonatal patients over the last 8 years

4. Hypothermia Background • Patient core body temperature : 32 - 34°C • Helps to counteract a decrease in oxygenation by reducing the brain’s oxygen requirements. • Neurological protection for patients with: • Sever head trauma • Cardiac/pulmonary distress • Other pathologies • Current methods: • Medications • Ice water baths • Cooling blankets • IV of 4°C crystalloid

5. Overview • Cooling offers a way to provide neurological protection for a patient on ECMO. • Current heat exchangers used on ECMO are not capable of rapidly inducing patient hypothermic conditions. • Solution: • Design of a more efficient heat exchanger that will work in conjunction with an ECMO circuit.

6. Overview • Users: • Neonatal ECMO patients • Customers: • Hospitals • Perfusionists • Customer Requirements: • More efficient means of inducing Hypothermia

7. Overview • Current Re-design: • Heat exchanger is compatible with existing water bath in circuit • Modeled similar to an oxygenator • Increased surface area for exchange – nonporous hollow polypropylene fibers • Priming volume maintained (60mL vs. ~65-70mL)

8. Features & Benefits • Needs/requirements of end-user: • Rapidly and accurately cools patient to desired hypothermic temperature (32-34°C) • Gradual rewarming of the patient’s blood <1°C/ 15mins • No clot or thromboemboli formation • Pressure sensor on outlet of heat exchanger • Safety of end-user: • No significant increase in required patient priming volume • Biocompatibility

9. Project Objectives – Spring 04 • Establish project objective: • Research efficient means of cooling • Project documents: • DHF, scientific paper, presentation • Heat transfer calculations: • Energy balance equations • Calculation of overall heat transfer coefficient (U) • Calculation of surface area (SA) • Calculate the number of fibers and priming volume • Development of fiber bundles in heat exchanger • Design of outer shell

10. Project Objectives – Future Direction • Fabrication and assembly of device • Wet-lab testing • Analysis • Possible redesign of device to fulfill any unmet requirements from previous device

11. Project Management • Individual Responsibilities: • Accomplishments • Remaining Tasks

12. Device Description • Non-porous polypropylene microfibers encased in a clear PVC housing • Efficient heat transfer (Thermal conductivity estimated at 11.7 W/mK from the Polymer Handbook) • Increased SA for exchange • Counter-current flow  maximizes heat transfer • Blood flows within the fibers • Decrease priming volume requirement at the expense of heat transfer

13. Design Alternatives • Fall 2003: • Cooling Block • Reasons for Rejection: • Surface area requirement • Spring 2004: • Hollow 3003 anodized aluminum tubing • Reasons for Rejection: • Could not achieve required surface area with a reasonable amount of tubes • Large priming volume • Manufacturing restraints

14. Quality System Considerations • Manufacturability: • Materials: • Polypropylene microfibers • PVC shell • Polyurethane epoxy • Methods: • Ension manufacture of fibers • Rapid prototyping or hand machining of PVC shell • Human Factors: • Ensures the safety and needs/requirements of the end user are met • Regulatory: • Class II • Predicate devices: All companies producing blood heat exchangers

15. Experimental Design • Heat transfer within patient can be correlated by the Pennes equation: • Mathematical modeling was used to find the desired surface area (SA) • Incorporation of SA into heat exchanger design • Subsequent fiber and priming volume calculations

16. Engineering Technologies/Methodologies • Solidworks 7.5 in.

17. Competitive Analysis • Competitors: • Non-invasive surface cooling • Other heat exchanger manufacturers (Medtronic, Gish Biomedical, etc) • Strengths: • More efficient heat exchange • No additional infused liquids • Weaknesses: • Requires constant monitoring of patient temperature • Requires extra pressure sensor

18. Constraints • Economic: • Costly manufacture • Small market (~1000/year) • Regulatory: • Priming volume • Biocompatible materials

19. Testing Requirements • FDA Requirements: • Preparation for Testing • Biological Compatibility Tests • Physical Integrity Tests • Performance Characterization

20. Projected Methods • Simulate a patient using a 2.5 - 5.0 L carboy • Utilizing a full ECMO circuit • Additional heat exchanger used for metabolic effects • Temperature set at 37 °C • Record heat exchange, water and blood-side pressure drops • Perform several 6 hour trials at various water and blood flow rates • Also test for blood damage

21. Acknowledgements • Dr. Carcillo • Mark • Children’s perfusionists