Methods of High-Frequency Assisted Airway Clearance

TSRC Pineywoods DistrictAnnual Spring Seminar

April 3-4, 2008David R. Barton, BA, RRT, RCP

Educational Coordinator

Respiratory Care Services

Medical City Dallas Hospital

Objectives

• Overview of Airway Physiology/HFO device interactions that enhance secretion clearance:

• Equal Pressure Point• Dynamic airway compression with flow

limitation• Clinical uses of positive airway pressure• Oscillatory Clearance Index

Objectives

• Types of High Frequency-Assisted Airway Clearance devices and mechanisms of action:

• Intrapulmonary Percussive Devices– Percussionaire– PercussiveNeb– MetaNeb

• High Frequency Chest Wall Compression– ThAIRpy Vest– Smart Vest

Objectives

• Types of High Frequency-Assisted Airway Clearance devices and mechanisms of action:

• Oscillatory Positive Expiratory Pressure Devices (Patient Powered)– Flutter VRP 1

– Accapela

• Evidence supporting use of the various devices

Historical Perspectives

• Research on many of these devices has been on-going for more than two decades.

• Eight lectures on airway clearance techniques were presented at the 17th Annual New Horizons Symposium at the 2001 AARC International Congress and published in Respiratory Care in July, 2002.

Historical Perspectives

• Followed 5 years later with a special Respiratory Care Journal Conference presenting review articles on: Airway Clearance: Physiology, Pharmacology, Techniques and Practice published in Respiratory Care, September and October, 2007.

Historical Perspectives

• Indeed, research continues today.

• Respiratory Care, March, 2008– An article by Alves, et al, relate a bench study

on performance characteristics of the Flutter at various inclinations and flows.

Historical Perspectives

• Dean Hess, PhD, RRT pointed out in his forward editorial to the Respiratory Care July, 2002 New Horizons Symposium articles and repeated in the Respiratory Care October, 2007 Journal Conference Summary there remains a dearth of high-level evidence related to airway clearance techniques.

• Studies are plagued with small sample sizes, crossover designs, surrogate outcome measures and statistical concerns.

Historical Perspectives

• However, Hess remains optimistic about these techniques when he states: “Does lack of evidence mean lack of benefit? Is the lack of evidence due to study methodology, or is there really no benefit from many techniques used to enhance secretion clearance? Although we should not be dogmatic about endorsing a therapy with absence of proof of its benefits, we must also not be dogmatic about abandoning a therapy because of absence of proof of its benefit – absence of proof in NOT proof of absence.”

D Hess, Respiratory Care July, 2007 Vol 47 No 7 pg 757

Airway Physiology/Device Interactions

• RTs must have an understanding of the principles of airway physiology/device interactions.

• We must know how a particular device works.

• Enables us to make appropriate decisions of which device to use under which circumstances.

Airway Physiology:Mechanisms of Mucus Mobilization

• Slug Flow– A semi-solid mucus plug is pushed from behind by expiratory air

flow.

• Annular Flow– Mucus moves along the lumen of the airway by being pulled along

by expiratory air flow or transported by cilia.

• Mist Flow– Aerosolized mucus that is exhaled as suspended droplets.

• Majority of airway secretion clearance occurs by slug and annular flow

• Expiratory flow is key to secretion clearance.CD Lapin, Resp Care, July 2002 Vol 47 No 7, p 779

Airway Physiology:Equal Pressure Point

Airway Physiology:Equal Pressure Point

• The EPP concept is integral to understanding how airflow limitation occurs.

• Initiated at normal lung volumes the EPP lies at the carina or large bronchi which are reinforced by cartilage and thus resist collapse.

Airway Physiology:Equal Pressure Point

• Cough generates supra-maximal, turbulent air flows (flow transients).

• These flows must speed up through the EPP and creates shear forces that move secretions cephalad.

• However, the turbulent flows cause faster pressure dissipation creating more potential for airway collapse at the EPP

• Dynamic airway collapse can also occur in disease states that causes increased compliance (CF, COPD)

• Even the larger airways may be compressed if frequent coughing has damaged the cartilage.

Airway Physiology:Mucus Plugging

• In order for cough or expiratory flow to mobilize secretions, it is necessary to get air behind the secretions.

• Mucus plugs can prevent inspiratory flow from getting behind the site of obstruction, making cough and airway clearance ineffective.

High-Frequency Devices

• Anecdotal discoveries made during early research on HFOV found that pulsatile gas flows at 3-30 Hz increased the volume of secretions in the upper airway.

• Later studies confirmed that the cephalad flow of secretions was accelerated during HFOV.

JB Fink, Resp Care July, 2002 Vol 47 No 7 pg 797

HFO: Mechanisms of Action

• Reduction in mucus viscoelasticity.

• Shear forces at the air-mucus interface applied at oscillatory frequencies that approximate cilia beat frequency.– HFO “resonates” with the cilia, nudging the

mucus layer upward.

• Redistribution of lung volume.

JB Fink, Resp Care July, 2002 Vol 47 No 7 pg 798

HFO: Mechanisms of Action

Normal Exhalation

Oscillatory Clearance Index

• OCI was developed by Scherer, et al, in 1995.

• Described conditions for optimal mucus transport:– Expiratory flow in the range of 1-3 L/s.– Oscillation frequency between 8-15 Hz.

• OCI derived to find optimal settings for IPV and HFCO.

TA Scherer, Chest 1998; 113; 1020

Oscillatory Clearance Index

Oscillatory Clearance Index

• Using surrogate outcomes of weight of expectorated sputum, PFTs and SpO2 they found:

• High-frequency airway and chest oscillation was as effective as CPT, was well tolerated and has the potential to reduce health-care costs by permitting self-administration of the modalities.

TA Scherer, Chest 1998; 113; 1020

Optimizing the Oscillatory Clearance Index

• The higher the frequency,• The higher the expiratory flow• The lower the inspiratory flow• The faster the inward displacement of the airway

wall during expiration• The slower the outward displacement during the

inspiration =• Higher OCI• Without any bias flow and with equal times of I:E

airway wall displacement, the OCI equals zero.TA Scherer, Chest 1998; 113; 1024

IPV

IPV Waveforms

Operational Characteristics

• Treatment duration approx 20 min.

• Impaction pressures of 25-40 psig.

• Frequency < 100 to 225 cycles/min.

• Non-oscillatory demand CPAP and intermittent mandatory ventilation (mandatory breath control button).

• Medication Nebulizer

PercussiveNeb

Operational Characteristics

• Pressure and flow waveforms similar to Percussionaire.

• Frequency up to 30 Hz.

• Medication Nebulizer.

MetaNeb

Operational Characteristics

• Pressure and Flow waveforms in CHFO mode similar to other IPV devices.

• Frequency of 230 cycles/min at 45 cmH2O on Higher Setting.

• Frequency of 190 cycles/min at 38 cmH2O on lower setting.

• CPEP adjustable from 0-30 cmH2O.

Vest

Vest Waveforms

Operational Characteristics

• Pulse frequency adjustable from 5-25 Hz.

• Pressure in the vest ranges from 28 mm Hg at 5 Hz to 39 mm Hg at 25 Hz.

OPEP DevicesFlutter VRP1

Flutter VRP1

Flutter VRP1 Operational CharacteristicsVariable +15o

L/M 30 60 120

+30o

L/M 30 60 120

Mean Pressure(cmH2O)

13 23 55 15 18 42

Mean Resistance(cmH2O/L/s)

28 28 25 28 18 20

Mean Frequency(Hz)

22 23 30 25 23 28

Mean Flow Amplitude

(L/s)

0.06 0.10 0.16 0.07 0.11 0.16

LA Alves, Resp Care, March 2008, Vol 53 No3 p 319-321

Flutter VRP1 Operational CharacteristicsVariable AW Clearance

EffectBest Expir Flow Best Inclination

Mean Flow

Huff

Low Flow and Vol for secretions in distal airways.

High Flow and vol for distal airways

-30o

+ 30o

Mean Pressure

PEP

0.2 L/s at PEP of 10, > 1.0 L/s at 20

+15o / +30o

Oscillation Frequency HFO > 0.2 L/s All except -30o

Flow Amplitude Flow Amplitude

> 1.4 L/s 0o / +15o / +30o

LA Alves, Resp Care, March 2008, Vol 53 No3 p 321

OPEP Devices: Acapella

Variable Blue

(Low Flow)

Green

(High Flow)

Mean

Exp. Pressure (Cm H2O)

3-24 6-21

Pressure Amplitude

(cmH2O)3-11 1-12

Oscillatory Frequency

(Hz)8-25 13-30

TA Volsko, Resp Care, Feb, 2003 Vol 48 No 2 pg 127

Airway Stability with HFO• Anecdotally, these devices could potentiate

dynamic airway compression and shift the EPP peripherally.

• Non-oscillatory PEP may be an effective way to stent the airways open and promote secretion mobilization with a “huff-effect”.

Stabilizing Airway with PEP

Thank You for your participation!

Discussion

Presentation available at:

www.rtconnection.org

david.barton@HCAHealthcare.com