This document can be used during university studies and once you graduate. It covers the theory and clinical reasoning behind various airway clearance techniques used in Respiratory Physiotherapy.
Theoretical Rationale for Secretion clearance techniques: (why
these work)
o Increase in expiratory flow
o Oscillation of airflow
o Increasing lung volumes
Physiological effect of increase in expiratory flow can be explained by the 2-phase gas-
liquid flow mechanism. (Book cites Zhao et al 2013)
o First pattern - mist flow (e.g. Cough)
Occurs when very fast expiratory flow rate shears the secreations off the
wall of the airway in small particles towards the oropharynx.
Patients need to be able to take in a deep breath in order to produce a
cough. For an effective cough, patients need to be able to:
inspire large volumes of air
create a intrathoracic pressure (through effective contraction of
abdominal and expiratory accessory muscles)
Have closure of glottis
Have airways that dynamically narrow but do not collapse.
o Second pattern - annular flow
When the increase in the expiratory flow rate moves the secretions which line the
airway in a wave like pattern towards the oropharynx.
In order for this to work:
Critical volume of secretions
Critical depth and stickiness of secretions
Need for an expiratory bias to airflow.
This means peak speed of cough (Peak Expiratory flow PEF) needs to
be 10% faster than peak speed of breathing in
Huff, vibs, flutter devices have shown to generate PEF that is at least 10% faster than PIF in
stable patients w CF.
Physiological effect of oscillating air flow (shaky air) DURING ACT
o Increase in expiratory flow rate
o Mechanical stimulation of ciliated cells of the airway - shaking can stimulate the
ciliated movement of the sputum
o Change the texture of the mucus to make it move easier.
Oscillating air flow can be created through:
o Manual techniques (onto chest wall or airway)
o Applying resistance to airflow at the mouth (PEP devices)
3-7Hz moves secretions, 13hz is ideal.
Physiological effect of increasing lung volumes
, By adding resistance to the expiratory airflow, positive back pressure is created within the
lungs.
o Positive back pressure within airways can help maintain the airways. (hence
increasing lung volumes)
o Increased lung volumes can allow air to get behind the secretions, and help facilitate
the movement of the mucus.
Increasing functional residual capacity of the lungs (make lungs less squished) can also help
increase lung volume.
o I.e. Positioning
o CPAP
o Breathing exercises.
THERAPIST DEPENDENT ACT'S
Postural drainage:
PD was one of the first ACT's suggested nearly a century ago (Ewart 1901)
PD uses gravity to aid the mucus towards the main bronchi
Can cause vomiting / micro-aspirations
o Common in children with CF
o Patients with chronic resp disease e.g. bronchiectasis
Modified Postural drainage is used more often now since early studies.
Studies in 1999 and 2007 showed PD to be more effective than PEP devices and ACBT alone,
suggesting gravity does bits. However, the study also showed that the head tilt may not be
necessary.
Contraindications - following meals, cardiac failure, severe hypertension, cerebral oedema,
aneurysms, severe haemoptysis, vomiting, after recent surgery, after recent trauma to head
or neck. Children with raised intracranial pressure or preterm infants (risk of periventricular
haemorrhage)
Patients with CF commonly have upper lobes and perihilar and apical segments of the lower
lobes are most severely affected.
Manual Techniques:
These are definitely the longest standing airway clearance strategy implemented into the
health care system.
o Percussion
o Vibrations
o Shaking
o Chest wall compressions
Rationale behind technique:
o Commonly used to loosen secretions, reduce fatigue, or to increase effectiveness of
other techniques.
o The techniques puts an intermittent positive pressure on to the chest wall, similarly
onto the lungs and the airways.
o This intermittent positive pressure of the structures can cause oscillation to the air,
as well as increase the expiratory flow.
o This oscillation and increase in flow of expiration, it is proposed to assist in secretion
clearance.
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