measuring functional residual capacity of ventilated neonates advisor: dr. bill walsh doug anderson...
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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