1. Measuring Neonatal Lung Volume
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
Neonatal Intensive Care Unit (NICU) includes 60 intensive and intermediate beds, a 3 bed ECMO unit, and 10 bed intensive care nursery
Methods must be simple, non-invasive, and allow free access to neonates

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. Problem Description
Problem: Too small a FRC results in the inability to oxygenate and consequently death because blood entering the lung actually exits the lung without coming into contact with a gas surface
Solution: Designing a device that measures FRC in neonates can allow doctors and researchers to optimize ventilator settings so as to prevent this sort of shunting and also provide them with better methods to assist the breathing in neonates especially those who are born premature and suffer from respiratory distress syndrome and other lung pathologies

5. Measuring FRC Helium Dilution Method Nitrogen Washout 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%

6. Previous Attempts to Measure FRC I
Critical Care Medicine (1980)
Estimating FRC of newborn infants receiving continuous positive airway pressure (CPAP)
Four-breath nitrogen washout technique
Reduces the period of breathing pure oxygen
Mechanical lung model
Infants with Respiratory Distress Syndrome (RDS)

7. Previous Attempts to Measure FRC II
Journal of Applied Physiology (1992)
Modification of computerized tracer gas (SF6) washout method
Designed for serial measurements of FRC and ventilation homogeneity in mechanically ventilated infants
Very low birth weight
Tidal volume down to 4 mL
Mild to moderate RDS
FRC increased with body weight
FRC (mL) = x weight (kg)

8. Previous Attempts to Measure FRC III
Pediatric Pulmonology (1997)
Compared standard N2 washout technique for measuring FRC with a modified technique using heliox as a washout gas
Volumes can be measured with high precision and reproducibility, even in premature infants with low lung volumes and/or high baseline FIO2
Correction factor may be needed because using heliox

9. Our Choice
A Method for Measuring Functional Residual Capacity in Neonates with Endotracheal Tubes

10. The Device

11. Results In Vitro In Vivo Confirmed expected exponential relationship
Real vs. Calculated: r = 0.995, p<0.001
In Vivo
Used in infants as small as 600 g
CPAP (cm H2O) 3
FRC
22.0  1.9
25.8  1.4 N 15 30

12. 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

13. 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
Obstructive diseases may delay equilibration
Research into subsequent efforts into this limitation is ongoing

14. Closed Loop Helium Dilution System for Measuring FRC

15. Assembling Prototype Compile list of necessary supplies and equipment
Procure or obtain access to all necessary items
Assemble and test prototype
Refine and upgrade prototype

16. Supplies and Equipment
Inexpensive Purchaseables
Medical grade tubing
Valves and stopcocks
Expandable membranes
Solenoid Valve
VUMC Equipment
Air Pumps
Digital Helium Meter
Pulmonary Function Machine

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
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.

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): May.
Critical Care Medicine. 8(11): Nov.
Journal of Applied Physiology. 73(1): July.
Pediatric Pulmonology. 23(6): June.

21. Questions