Measuring Functional Residual Capacity of Ventilated Neonates

Advisor: Dr. Bill Walsh

Doug Anderson

David Lammlein

Janine McKinnon

BackgroundBackground 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

Functional Residual Capacity (FRC)

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

Mechanical Ventilation in Neonates

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 O2?

Trial and error from years of experience is used to make adjustments to get sufficient oxygenation

Extracorporeal Membrane Oxygenation (ECMO)

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

Problem DescriptionProblem DescriptionProblems

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

Measuring FRCMeasuring 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%

Our ModelOur Model

1978 - A Method for Measuring Functional Residual Capacity in Neonates with Endotracheal Tubes

€

FRC = VCi

C f

−1 ⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟

C∧

f = CHe' (t2)

CHe' (t1)

CHe' (t2)

⎡

⎣ ⎢

⎤

⎦ ⎥

t2 t2 −t1( )( )

The DeviceThe Device

Reported ResultsReported 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

CPAP (cm H2O)

0 3

FRC 22.0 1.9 25.8 1.4

N 15 30

Evita 4 VentilatorEvita 4 Ventilator

Collins Helium AnalyzerCollins Helium Analyzer

Millipore Peristaltic PumpMillipore Peristaltic Pump

AdvantagesAdvantages

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

LimitationLimitation

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

Assembling Prototype 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

Supplies and EquipmentSupplies and Equipment

Medical grade tubing Valves and stopcocks Anesthesia bag Solenoid Valve

Inexpensive Purchaseables

VUMC Equipment

Heliox gasHeliox gas

Air PumpsAir Pumps

Helium MeterHelium Meter

Design GoalsDesign 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

Market PotentialMarket 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.

Social ImpactSocial Impact

Profound: Families and friends of critically ill neonates

Minimal: Environment, helium is an inert gas

ReferencesReferences

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.

QuestionsQuestions