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• Define HFT and how it is accomplished with a nasal cannula
• Explain how the dynamics of flow through the nasopharynx improve respiratory efficiency and support work of breathing
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• Explain the properties of Heliox gas mixture and how heliox can be beneficial in the respiratory system
• Understand how the characteristics of HFT facilitate the breathing of heliox via a nasal cannula
• Understand the patient population that can benefit from heliox HFT
A Review of the HFT and Mechanisms of Action
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Heliox andHeliox via HFT
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High Flow Nasal Cannula
Generic term for flow rates that exceed conventional nasal cannula flow rates
High Flow Therapy
•Exceed a patients inspiratory flow demand •Flushes out the anatomical dead space, thus creating
an internal reservoir
HFT is between 25 – 35 L/min in adults, or 4-8 L/min in infants
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Nasopharynx
Prior to reaching alveoli, gas must be:
• Warmed
• Humidified
• Cleaned
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Nasopharyngeal Structure
• Non-respiratory anatomical dead space
• Impacts breathing efficiency
• Provides challenges to conventional non-invasive respiratory support
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Fresh atmospheric gas mixes with
end-expiratory gas
End-expiratory gas is
low in oxygen and high in carbon
dioxide
Alveolar gases are different
from atmospheric
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Nasopharynx•Cleaning•Warming •HumidificationConducting
Airways
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Reduced anatomical dead space
compensates for increased
physiological dead space
Flushing reduces anatomical dead space
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• Importance in conditioning of breathing gases to body temperature and saturated with water vapor.
• An effective tool to support spontaneous breathing that goes beyond conventional nasal cannula.
• Works with your body’s respiratory anatomy and physiology to improve breathing efficiency through basic mechanisms.
• A non-invasive means of respiratory support that is simple to apply and improves patient comfort.
Key supporting literature includes:•Dysart et al. Respir Med 2009;103: 1400-1405 •Frizzola et al, Pediatr Pulmonol 2011;46:67-74 12
Further education and information surrounding the Mechanisms of Action of High Flow Therapycan be found at:Vapotherm website (http://www.vtherm.com)Highflow website (http://www.highflow.org)
Helium was discovered in the late 19th century.
It is a biologically inert, noble gas that has many useful applications due to its physical properties such as low molecular weight and low density.
When mixed with oxygen for breathing applications to replace nitrogen as the balance or carrier gas, we have what’s know as heliox.
Dr. Barach began studying and advocating the use of Heliox for medical purposes in the 1930’s.
The low density of Helium is the physical property which makes Heliox ideal for certain medical applications.
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* 79% helium and 21% oxygen, commonly known as 80 /20 heliox
Air Helium Oxygen Heliox*Nitrogen
Heliox decreases RAW in areas of turbulent flow
How and where does a lower density gas reduce RAW?
Re= Reynolds Numberρ = densityν = velocityr= radius
η = viscosity
Laminar Flow occurs at Re < 2000Turbulent Flow occurs at Re > 2000
vr
Re
Area of greatest effectArea of obstruction
Net offset in RAW and WOB
Inhalation: Better tidal volume + distribution =
Oxygenation
Key Applications Benefits
Asthma (severe) Reduced airway resistance (improved laminar flow, lower density) Reduced work of breathing
Acute upper airway obstruction Improved tidal volumes
Croup Reduced insp/expiratory ratios
COPD exacerbations Increased C02 clearance
Vent weaning Improved homogeneity of gas distribution
Pulmonary Rehabilitation Improved exercise tolerance
Aerosol drug delivery Better deposition
Mechanics and energetics of breathing helium in infants with bronchopulmonary
dysplasia
Wolfson et al. J Pediatr 1984, 104(5): 752-7
Mechanics study showing:
•Decrease pulmonary resistance and work of breathing•Reduced risk of respiratory muscle fatigue
Growth and development in a heliox incubator environment: a long-term safety
study
Singhaus et al. Neonatology 2007, 91(1):28-35
•rabbits pups raised in heliox environment compared to controls. •No difference in growth parameters or developmental milestones
Heliox attenuates lung inflammation and structural alterations in acute lung injury
Nawab et al. Pediatr Pulmonol 2005;40:524-32 42
•Lung morphology showed improved distribution of heliox gas through the lung
•Pro-inflammatory mediators and matrix remodeling proteins levels were significantly lower with heliox versus nitrogen-oxygen mix
Blinded, RCTs in Acute AsthmaHeliox versus air-oxygen
Author / Data # Patients
Key Findings
Rose 2002 36 Less dyspnea
Kress 2002 45 Improved FEV1
Kudukis 2002 18 PP, PEFR and DI improved
Carter 1996 11 FEF25-75 and PEFR%
Henderson 1999
205 PEFR% improved
All in favor of Heliox
Prospective Randomized crossover trial with heliox in COPD (n = 19)
Jolliet et al. Crit Care Med. 1999 Nov;27(11):2422-9
Heliox compared to air-oxygen
•↓ Inspiratory / total time ratio (p < 0.05)•↑ PIFR (p < 0.01)•↓ PaCO2 (p < 0.01) and Dyspnea (p < 0.05)
• Cannula gas flow should exceeds a patient’s spontaneous inspiratory flow rate to inhale the precise gas mixture
• The nasopharynx becomes an internal reservoir of heliox.
• The effects of helium is not hampered by the entrainment of room air.
• The therapeutic affect can be achieved using the minimally invasive interface.
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