Measuring Functional Residual Capacity of Ventilated Neonates

1. Measuring Functional Residual Capacity of Ventilated Neonates Advisor: Dr. Bill Walsh Doug Anderson David Lammlein Janine McKinnon

2. Background • The Division of Neonatology at Vanderbilt Children’s Hospital has an interest in determining the Functional Residual Capacity (FRC) in neonates who are mechanically ventilated • Methods must be simple, non-invasive, and allow free access to neonates • Method must be employed in the Neonatal Intensive Care Unit (NICU) which includes 60 intensive and intermediate beds, a 3 bed ECMO unit, and 10 bed intensive care nursery

3. Functional Residual Capacity (FRC) • Functional Residual Capacity (FRC) of the human lung is the volume remaining in the lungs at resting expiratory level • Equivalent to the alveolar volume (Va) which contains 60-70% of the total lung volume • Normal FRC in adults is 1.8 to 3.4 L • Estimated FRC in healthy neonates 5 to 12 mL

4. Mechanical Ventilation in Neonates • The most common admitting diagnosis to the NICU is respiratory distress • Indications for Mechanical Ventilation • Hypoxemia/cyanosis from lung disease (inadequately treated with supplemental O2 alone or with CPAP—continuous positive airway pressure) • Hypoventilation or frank apnea • Increased work of breathing • Severe systemic disease especially with circulatory failure, requiring airway control • Determination of Ventilator Settings • X-rays can be used to help determine PEEP and O2 saturation levels • Have I optimized the lung volumes? • Is the lung volume the cause for low pO2? • Trial and error from years of experience is used to make adjustments to get sufficient oxygenation

5. Extracorporeal Membrane Oxygenation (ECMO) • ECMO is used when a ventilator does not provide sufficient oxygen or remove enough carbon dioxide. • ECMO is a form of long-term heart-lung bypass used in infants, children, and adults in cardiac and/or respiratory failure despite maximal medical treatment • Similar to heart-lung bypass used in the operating room • Essentially all the blood is pumped out of the body and run through artificial heart-lung machine to oxygenate and then it is returned to the body • Babies are at a greater risk for death because the process constitutes 20% mortality • Respiratory failures for infants include: • Acute Respiratory Distress Syndrome (ARDS) • Pneumonia • Sepsis • Congenital Diaphragmatic Hernia (CDH) • Pulmonary Hypertension • Inborn Errors of Metabolism • ECMO takes over the work for the lungs so they can rest and heal

6. Problem Description Problems • Too small a FRC can result in the inability to oxygenate blood and possibly death if blood entering the lung actually exits the lung without coming into contact with an exchangeable gas surface—shunting • Current trial and error methods used to adjust ventilator settings can cause too much PEEP or CPAP which in turn can cause barotraumas, preventing the blood from going into the lung Solution • Design a device that measures FRC in neonates Medical/Research Benefits • Can allow doctors and researchers to optimize ventilator settings so as to prevent this sort of shunting or to prevent over oxygenation of neonates coming in at 100% O2 with air in lungs • Can also allow physicians to utilize appropriate methods to facilitate breathing in neonates suffering from lung pathologies, and specifically allows physicians to assess the need for ECMO

7. Measuring FRC • Helium Dilution Method • Inspiration of known [He] • Gas in lungs dilutes He and [He] drops • Gases equilibrate • Measure difference in [He] to determine initial lung volume • Nitrogen Washout Method • Unknown FRC contains about 78% N2 and an unknown amount of O2 and CO2 • Washout N2 by breathing 100% O2 • Exhale so that expired [N2] falls between 1 and 1.5%

8. Our Model 1978 - A Method for Measuring Functional Residual Capacity in Neonates with Endotracheal Tubes

9. The Device

10. Reported Results • In Vitro • Confirmed expected exponential relationship • Real vs. Calculated: r = 0.995, p<0.001 • In Vivo • Used in infants as small as 600 g

11. Evita 4 Ventilator

12. Our Prototype

13. Advantages • Easy to set up • Uses common equipment • Can be used for a large range of infants • Useable with both CPAP and ventilator support • Relatively inexpensive

14. Limitation • Breathing rate and tidal volume assumed constant • No calculation if minute ventilation (respiratory rate X tidal volume) changed by more than 25% over measurement period • This should not be an issue in our use since the ventilator will control the minute ventilation. • Obstructive diseases may delay equilibration

15. Assembling Prototype • Completed: • Compiled list of necessary supplies and equipment • Either procured or obtained access to almost all necessary items, contacts: Chris Lynn, Dan Lindstrom • Current and Future Work • Assemble and test prototype • Refine and upgrade prototype

16. Supplies and Equipment Inexpensive Purchaseables • Medical grade tubing • Valves and stopcocks • Anesthesia bag • Solenoid Valve VUMC Equipment Heliox gas Air Pumps Helium Meter

17. Design Goals • Use primarily existing equipment • Avoid complicated, dangerous, or invasive procedures • Allow for uncooperative nature of infants • Mobility of device • Continued free access to neonate

18. Market Potential • Clients: Neonatal Intensive Care Units • Because the device can assess the need for ECMO, it has the potential to save hospitals thousands of dollars • Standard Ventilation  $2000/day (Vanderbilt University Hospital) • ECMO  $5000/day (Vanderbilt University Hospital) • Can also save cost because optimal ventilator settings lead to maximum oxygenation which should help curing of lung pathologies • Competitors: No current patents exist on this exact device; however, other more costly methods (i.e. tomography, ultrasonic flow meter) exist. • Production: Creating simple modification to existing equipment will result in lower production costs and overhead. Building this system from scratch would cost about $2000 for the necessary equipment.

19. Social Impact • Profound: Families and friends of critically ill neonates • Minimal: Environment, helium is an inert gas

20. References • Schwartz JG, Fox WW, Shaffer TH. A Method for Measuring Functional Residual Capacity in Neonates with Endotracheal Tubes. IEEE Trans. On Biomed. Engineering. 25(3): 304-7. 1978 May. • Journal of Applied Physiology. 73(1): 276-83. 1992 July. • Pediatric Pulmonology. 23(6): 434-41. 1997 June.

21. Questions