Respiratory Physiotherapy Techniques for ICU Patients

Original Editor - Chidile Muonwe

Top Contributors - Merinda Rodseth, Tarina van der Stockt and Kim Jackson  

Introduction[edit | edit source]

Patients admitted in the intensive care unit (ICU) are at high risk of developing respiratory complications due to immobility and/or the use of mechanical ventilators.[1][2][3] Many patients are also admitted to the ICU due to acute respiratory failure.[2] Physiotherapy is an essential component in the management of patients admitted to the ICU.[4] Physiotherapists in the ICU aim to prevent respiratory complications from developing or mitigate the already developed problems.[5] The most common goals of physiotherapy for respiratory dysfunction in the ICU include airway secretion clearance, maintenance or improvement of lung volume, optimization of oxygenation, and maintenance or training of inspiratory muscle strength.[1][3][4][6][7] These general goals can be achieved using appropriate physiotherapeutic techniques and devices which are discussed below.

Positioning[edit | edit source]

Positioning is one of the most effective interventions for respiratory dysfunction and is primarily governed by the influence of gravity.[8] Body positioning has a direct impact on respiratory mechanics and its physiological effects include optimizing oxygen transport and thereby oxygenation through improved Ventilation-Perfusion (V/Q) matching, increasing lung volume, reducing the work of breathing, minimizing the work of the heart, and enhancing mucociliary clearance (postural drainage).[1][7][8][9]

Selecting the most efficient body position is based on the day-to-day evaluation findings as well as clinical reasoning around the desired effect/benefit, whether it be secretion clearance or recruitment of lung volume with improved oxygenation.[8][10]

Side-lying with the affected lung uppermost increases the lung volume to the uppermost lung which enhances the resolution of atelectasis.[1][9][11] This position also facilitates drainage from broncho-pulmonary segments.[1][9] Keeping the non-affected lung at the bottom has the added benefit of increasing oxygenation as gravity directs perfusion to the bottom lung.[10][12] The side-lying position with the affected lung uppermost is also useful for applying other respiratory techniques such as Manual Hyperinflation (MHI) or ventilator hyperinflation (VHI).[3]

Postural drainage utilises gravity-assisted and modified gravity-assisted positions to drain secretions from specific segments/areas of the affected lung (postural drainage).[7][8][11] Positions specific to each lung segment are related to the anatomy of the bronchial tree and by placing patients in specific recumbent or semi-recumbent positions enables gravity to move secretions from the peripheral airways in the affected lung segment to the central airways in order to be removed.[3][7][8] Secretion clearance can be further enhanced in the postural drainage position with the use of basic manual techniques.[7]Follow this link to see info graphs with postural drainage positions.

Patients must be assessed to determine if the position to be used is safe for their condition.[13] Contraindications for a head-down tilt position (Trendelenburg) include cardiac failure, cerebral edema, severe hypertension, aortic and cerebral aneurysms, abdominal distension, gastro-esophageal reflux, severe hemoptysis, recent surgery and trauma to the head and neck, increased intracranial pressure and haemodynamic instability.[3][10][14] If the position is not suitable for the specific patient, then a modified postural drainage position in the horizontal position can be used.[10] When the patient is placed in a gravity-assisted position, the patient must be observed for any signs of distress and their vital signs must be monitored.[8]

Manual Hyperinflation and Ventilator Hyperinflation[edit | edit source]

Hyperinflation is aimed at preventing pulmonary atelectasis, recruitment of collapsed alveoli, improvement of lung oxygenation, improvement of lung compliance, and mobilization of airway secretions.[3][9][11][17] Manual hyperinflation (MHI) is a technique that involves the manual delivery of a slow deep inspiration with a resuscitator bag, an inspiratory hold of 2-3 seconds, followed by a rapid expiration (quick release of the bag) to enhance expiratory flow that mimics a forced expiratory technique.[3][9][17] During MHI the patient is disconnected from the ventilator and attached to a manual resuscitation bag through which a larger than normal inspiratory tidal volume (1.5-4 times the baseline tidal volume) is administered to the patient at a pressure not exceeding 40 cmH2O.[3][8][11][17] There are three distinct components to MHI:[3][8]

  • Slow deep inspiration increasing the tidal volume over a 3 second period
  • Inspiratory hold of 3 seconds to recruit poorly ventilated alveoli
  • Quick-release/expiration to increase expiratory flow

Ventilator Hyperinflation (VHI) is achieved by altering the settings on the patient's ventilator.[3] VHI has potential advantages over the MHI as no ventilator disconnection is needed. These advantages include the maintenance of positive end-expiratory pressure (PEEP), decreased infection risk, control of ventilator parameters and can be more easily reproduced.[3][18]

Hyperinflation in combination with postural drainage can result in greater efficiency of secretion removal.[3] Hyperinflation is contraindicated in patients with cardiovascular instability, head injuries, raised intracranial pressure (ICP >25mmHg), undrained hemothorax or pneumothorax, congestive heart failure, severe pneumonia, acute bronchospasm, patient on high PEEP, arterial hypotension and large emphysematous bullae, among others.[3][8][11]

Active Cycle of Breathing Technique[edit | edit source]

The Active Cycle of Breathing Technique

Active cycle of breathing technique (ACBT) aims at secretion clearance, recruitment of lung volume, and improving chest expansion and lung compliance.[3][8][10] It consists of cycles involving three breathing techniques performed in sequence:[3][8][10]

  • Breathing control
  • Thoracic expansion exercises (TEE) and
  • Forced expiratory technique (FET).

ACBT can be used on both spontaneously breathing and intubated patients who are conscious and understands and obeys instruction. It is a flexible technique where the repetition and order of each component can be adapted according to each patient’s needs.[3] ACBT is best performed in upright sitting but can also be combined with manual chest techniques and other devices and positions especially postural drainage or modified postural drainage positions.[3] Patients can continue with this technique independently after the physiotherapist has instructed them on how to perform it.

Breathing control (BC) incorporates the patient breathing at their normal rate and tidal volume.  A diaphragmatic breathing pattern is encouraged where the patient places one of their hands on their upper abdomen to facilitate breathing with the lower chest while relaxing the upper lung segments and shoulders.[3][10] The patient is encouraged to feel the abdomen rise during inspiration and fall during expiration.[10] Breathing control allows for recovery from fatigue and breathlessness which may be elicited by the more active components of the cycle and the duration will depend on the patient’s recovery rate.[3][10]

Thoracic Expansion Exercises (TEEs) are deep breathing exercises (DBEs) where the patient breathes at large volumes, close to the vital capacity and it is often combined with a 3-second end-inspiratory hold.[3][10] The breath-hold allows additional time for the obstructed lung segments to also fill, assisting in re-expanding the lung tissue.[3][10] Thoracic expansion exercises aim to loosen secretions, improve ventilation by re-expanding lung tissue and deliver sufficient volume for FET. TEEs should be limited to 3 or 4 as the patient may hyperventilate and fatigue. Breathing control may be performed between TEEs to allow the patient to rest.[3] To promote air entry to areas where it may be limited, the physiotherapist may place their hand or the patient’s hands on the chest wall over the affected segment providing proprioceptive input for the underlying lung tissue.[3] At the end of inspiration the patient may be encouraged to add a “sniff” in order to further increase lung volume.[3][10] This “sniffing manoeuvre” is not appropriate in patients who are hyperventilating or hyperinflated.[3] Thoracic expansion exercises are then followed by FET.

Forced expiratory technique (FET) consists of one or two forced expirations (huffs) followed by breathing control.[3][10] The aim of FET is to help clear secretions with less change in pleural pressures and less effort compared to a cough.[3] Forced expiratory technique is initially performed at low lung volumes to mobilize secretions from the small peripheral airways. Once the secretions have been mobilized to the larger more proximal airways a huff at a high lung volume is performed to move secretions into the mouth for expectoration.[3][10] This technique is more effective when combined with postural drainage.[3] Following 1-2 huffs, the patient continues with BC as a recovery phase, the length of which is dependent on the patient.[3] Patients who are intubated may find it difficult to perform TEE if they are on a ventilator setting that prevents breath-holding.

Manual Chest Techniques[edit | edit source]

Manual chest techniques are frequently used by physiotherapists when treating patients in ICU and involve applying force externally to the chest wall in order to facilitate secretion clearance.[3][11] These techniques include percussion (chest clapping), vibrations, shaking, chest compressions at the end of expiration to support coughing and rib springing.[3] The purpose of these techniques is to loosen and mobilise secretions from the peripheral to the central airways.[3][9][11] The mechanical energy produced by manipulating the chest wall is transmitted to the airways and aids in loosening and mobilising the secretions while also enhancing expiratory flow.[1][8]


Percussion is performed with the hands cupped, using rhythmic flexion and extension of the wrist on the chest wall of the patient over the affected lung segment.[3][9][11] Percussion is preferably not performed directly on the skin, but over a layer of clothing or a towel to prevent sensory stimulation of the skin.[1] Chest wall vibrations and shaking are performed by the therapist placing both their hands on the patient’s chest wall and applying an oscillatory movement combined with chest wall compression, initiated at the end of inspiration and continued throughout expiration.[1][3] Vibrations are a finer and higher frequency movement compared to shaking. Manual chest techniques are often performed with the patient in a gravity-assisted postural drainage position, or in side-lying.[3][8] In spontaneously breathing patients, manual chest techniques are often combined with TEEs and FETs as part of the ACOB.[3]

Manual techniques are contraindicated in patients with cardiovascular instability, thoracic/rib fractures, severe osteoporosis, where skin integrity is lost (over open wounds/burns), severe haemoptysis, pulmonary oedema and worsening bronchospasm.[1][3]

Nebulisation[edit | edit source]

Many medications used to treat respiratory disease can be administered directly to a patient’s respiratory system by nebulization (inhalation).[3][11] During nebulisation solutions are converted to aerosol droplets that can be inhaled or delivered to the lungs. The proportion of dose received by the lungs is therefore enhanced which reduces the dosage needed and the side effects of the medication.[3][11] Nebulising a patient with saline/bronchodilator/mucolytic agents before physiotherapy intervention will alleviate bronchospasm and decrease the viscosity of the mucus/sputum in order to facilitate the removal of secretions.[7] This procedure can be performed on both intubated and spontaneously breathing patients and can be combined with postural drainage positions to assist with the drainage of secretions.[14]

Airway Suctioning[edit | edit source]

Closed Suction System
Sterile Suction Catheter for open suctioning

Suctioning is an important procedure that aids secretion removal from the airways.[11] It is essential in clearing retained pulmonary secretions from central airways and to maintain a patent airway in intubated patients.[19] Suctioning of patients who are unable to clear their secretions may reduce the incidence of pulmonary complications such as pneumonia.[19] Suctioning can be achieved through open or close methods in intubated patients.[11] In open suction, the patient is disconnected from the ventilator and a disposable suction catheter is inserted down the patient’s artificial airway.[11] The disadvantage of this method is the derecruitment of the lungs due to the loss of the patient’s PEEP when opening the airway circuit. Closed suctioning involves a suction catheter placed in a protective sheath and connected directly to the ventilator.[11] The smaller-sized catheter, which is about half of the endotracheal tube (ETT) in diameter, is passed through an opening down the ETT. Closed suctioning poses fewer risks from environmental cross-contamination as no disconnection is needed.[11] Pre-oxygenation with 100% oxygen for 1-2 minutes is recommended before suctioning to prevent hypoxemia.[11] Suctioning should be limited to 15-20 seconds while intermittently opening and closing the suction catheter without closing it for more than 5 seconds at a time.[11] Suction can also be achieved through the oronasal route and can be used in intubated and non-intubated patients to remove accumulated secretions in the oronasal region that may lead to micro-aspiration and increase the patient’s risk of ventilator-associated pneumonia.[13] Some of the side effects of suctioning include episodic hypoxemia, damage to the airway, bronchoconstriction, cardiac arrhythmias, increased intracranial pressure, hemodynamic instability, bacterial contamination and increased oxygen consumption, hence care must be taken and patient’s vital signs must be monitored constantly while performing suctioning.[1][11][19] Pre-oxygenation and optimal technique minimize the occurrence of these side effects.

Incentive Spirometry[edit | edit source]

Flow-incentive spirometry
Volume-incentive spirometry

Incentive spirometry (IS) utilises a device to provide visual feedback in order to encourage patients to breathe deeply.[1][10] IS is used for patients who are cooperative and able to follow instructions. It is recommended for spontaneously breathing patients who have developed atelectasis, poor inspiratory muscle strength and reduced oxygenation and is often used as a prophylactic therapy to patients at risk of developing the above-mentioned complications.[3][10] The incentive spirometer is a small and portable device that the patient can also use effectively on their own after sufficient instruction is received from a physiotherapist.[14] There are 2 types of incentive spirometers:[10]

  • Flow-incentive spirometry - the magnitude of airflow during inhalation is indicated by the number of balls and the level to which they rise
  • Volume-incentive spirometry - the volume of air displaced during inhalation is indicated on a scale marked on the device.

The incentive spirometer is activated by inspiration. Patients are instructed to take a slow deep breath through the mouthpiece with their lips sealed around the mouthpiece to maximally distribute ventilation.[3] Ongoing inspiration is encouraged by visual feedback, for example, a ball rising to a pre-set marker.[3] Depending on the purpose, the deep inspiration can be followed by an inspiratory hold for 3-5 seconds, normal expiration, or FET to help clear up secretions.[3][10] To enhance performance, the physiotherapist can place his/her hands over the patient’s basal lung segments, while verbally encouraging the patient to breathe into their lower lung segments while inhaling through the incentive spirometer. Patients should be monitored during IS to avoid hyperventilation, the use of accessory respiratory muscles and fatigue.  

Positive Expiratory Pressure Devices[edit | edit source]

Positive Expiratory Pressure (PEP) is another secretion clearance technique that involves the patient breathing out against resistance in order to create positive airway pressure.[3][8] PEP involves the use of devices to deliver positive pressure to the airways. PEP devices commonly utilize a one-way valve that allows unrestricted inspiration and resistance to expiration through a resistor valve or an orifice.[3] The resultant positive pressure produced during expiration encourages airway splinting, preventing airway collapse. The air accumulated behind the secretions also forces the secretions from the peripheral to the central airways for easier clearance.[3][8] Following these effects, the main indications for PEP therapy are therefore retained secretions and atelectasis.[3] There are three types of PEP devices:[10]

  • flow resistor - patients exhale against a fixed-size orifice based on age and expiratory flow
  • threshold resistor - patients exhale against an adjustable spring-loaded valve or reverse Venturi device
  • vibratory PEP (acapella and flutter) - patients exhale against a threshold resistor with an expiratory valve oscillating at 10-30Hz

The vibratory PEP device is most suited for secretion clearance.[10] During PEP therapy the patient will breathe for 10-20 breaths/cycle up to 4-8 cycles/session. After each cycle, the patient can make use of FET or supported coughing to clear secretions.[9][10]

PEP therapy may be used in combination with positive inspiratory pressure (PIP) delivered via non-invasive ventilation (NIV) such as continuous positive airway pressure (CPAP), Variable/Bi-Level Positive Airway Pressure (BiPAP/VPAP), Auto-adjustable Positive Airway Pressure Device (APAP) and intermittent positive pressure ventilation (IPPV).[3]

Non-Invasive Ventilation[edit | edit source]

Non-Invasive Ventilation

Non-Invasive Ventilation (NIV) is a technique where positive pressure is administered to the lungs and airways without the need for an endotracheal or tracheostomy tube.[3] NIV devices are used to improve gas exchange, improve lung volume in order to keep the airway open during respiration, reduce the work of breathing and alleviate symptoms of respiratory insufficiency.[3] These devices are not primarily used for airway secretion clearance but are reserved for patients with severe disease, hypoxia, inspiratory muscle weakness, or dyspnoea. They can however be useful adjuncts for airway clearance in combination with other techniques such as PEP and ACOB for individuals who have difficulty expectorating.[3] NIV devices function on similar principles, but the difference between CPAP, V/BiPAP, and APAP lies in the delivery of variable pressure. The CPAP device delivers single constant positive pressure during inspiration and expiration. BiPAP/VPAP devices deliver two types of pressure: prescribed inspiratory positive airway pressure (IPAP) and a lower pressure during exhalation (EPAP).[3] These devices are mostly prescribed for patients with obstructive sleep apnoea (OSA) and nocturnal hypoventilation.[3] CPAP is usually recommended as the first therapy option, but BiPAP support may be more effective in cases where patients require high-pressure settings or low oxygen levels or when CPAP fails to adequately alleviate symptoms.[3] The physiotherapist must have a thorough understanding of the underlying pathological processes contributing to the patient’s respiratory distress in order to choose the most appropriate PEP device to suit the respiratory needs of the patient.[3]

Intermittent Positive Pressure Ventilation Devices[edit | edit source]

Intermittent positive pressure breathing (IPPB) devices are used to maintain positive pressure to the airways of non-intubated patients during inspiration, with the airway pressure returning to atmospheric pressure during expiration.[3] Intermittent positive pressure breathing assists in increasing tidal volumes and reduces shortness of breath and atelectasis while reducing the work of breathing during inspiration.[3] The following parameters can be set by the physiotherapist on the IPPB device: the FiO2, flow rate, trigger sensitivity and peak inspiratory pressure according to the needs of each individual patient.[3] The position of the patient during IPPB depends on the indication for treatment but should be comfortable.[3] A breathless patient should ideally be positioned in a semi-Fowlers position; alternatively, IPPB may also be administered in a modified postural drainage position. The patient is instructed to close their lips firmly around the mouthpiece and attempt a slight inspiratory effort which will trigger the inspiratory flow of air. The patient should then relax and allow the machine to assist them with deep inhalation.[3]

IPPB is contraindicated in patients with tension pneumothorax, lung abscess, severe haemoptysis, bronchial tumor, intracranial pressure above 15 mmHg, haemodynamic instability, tracheo-oesophageal fistula and recent oral or facial surgery.[3][13]

Inspiratory Muscle Training[edit | edit source]

POWERbreathe IMT device

Inspiratory muscles, like other skeletal muscles, are at risk of atrophy and weakness when not used optimally. Long-term immobilisation (bedrest) and mechanical ventilation can cause pronounced muscle atrophy which includes the inspiratory muscles, resulting in inspiratory muscle weakness, loss of inspiratory muscle endurance, difficulty in weaning from the ventilator, as well as many other respiratory complications.[1][9][20] It is therefore essential that physiotherapists working in the ICU focus on minimising deconditioning of the inspiratory muscles by intervening prophylactically.[4] Inspiratory muscle training (IMT) involves inspiration against resistance or pre-targeted pressure thresholds in order to improve the strength and function of the respiratory muscles.[1][3][9][20] Techniques such as incentive spirometry, deep breathing exercises, ACBT, and the use of inspiratory muscle training devices such as a spring-loaded Threshold® IMT or POWERbreathe® device are effective in preventing and retraining inspiratory muscles.[9][21]  Inspiratory muscle training devices and techniques are safe to use in all intubated patients provided they can understand how to use the device and breathe spontaneously for short periods.

Resources[edit | edit source]

References[edit | edit source]

  1. 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 Malone DJ, Bishop KL. Acute Care Physical Therapy : A Clinician’s Guide, Second Edition [Internet]. Vol. Second edition. Thorofare, NJ: SLACK Incorporated; 2020 [cited 2021 Mar 5].
  2. 2.0 2.1 Connolly B, Barclay M, Blackwood B, Bradley J, Anand R, Borthwick M, Chikhani M, Dark P, Shyamsundar M, Warburton J, McAuley DF. Airway clearance techniques and use of mucoactive agents for adult critically ill patients with acute respiratory failure: a qualitative study exploring UK physiotherapy practice. Physiotherapy. 2020 Sep 1;108:78-87. DOI:10.1016/
  3. 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 3.11 3.12 3.13 3.14 3.15 3.16 3.17 3.18 3.19 3.20 3.21 3.22 3.23 3.24 3.25 3.26 3.27 3.28 3.29 3.30 3.31 3.32 3.33 3.34 3.35 3.36 3.37 3.38 3.39 3.40 3.41 3.42 3.43 3.44 3.45 3.46 3.47 3.48 3.49 3.50 3.51 3.52 3.53 3.54 3.55 3.56 3.57 3.58 3.59 3.60 3.61 3.62 Main E, Denehy L, editors. Cardiorespiratory Physiotherapy: Adults and Paediatrics E-Book: formerly Physiotherapy for Respiratory and Cardiac Problems. 5th ed. Elsevier Health Sciences; 2016 Jun 7
  4. 4.0 4.1 4.2 Denehy L, Granger CL, El-Ansary D, Parry SM. Advances in cardiorespiratory physiotherapy and their clinical impact. Expert review of respiratory medicine. 2018 Mar 4;12(3):203-15. DOI:10.1080/17476348.2018.1433034
  5. Gosselink R, Roeseler J. Physiotherapy in critically ill patients. The ESC Textbook of Intensive and Acute Cardiovascular Care. 2015 Feb 26:284.
  6. Troosters T, Bott J. Respiratory physiotherapy. IN: Palange P, Rohde G. (eds.) ERS Handbook of Respiratory Medicine. 3rd ed. European Respiratory Society; 2019. p.232-238.
  7. 7.0 7.1 7.2 7.3 7.4 7.5 Gupta L, Gupta H. Physiotherapy for Respiratory Conditions. Advanced nursing & patient care international journal. 2018;1(1):180003.
  8. 8.00 8.01 8.02 8.03 8.04 8.05 8.06 8.07 8.08 8.09 8.10 8.11 8.12 8.13 8.14 Swaminathan N, Praveen R, Surendran P. The role of physiotherapy in intensive care units: a critical review. Physiotherapy Quarterly. 2019;27(4):1-5. DOI:10.5114/pq.2019.87739
  9. 9.00 9.01 9.02 9.03 9.04 9.05 9.06 9.07 9.08 9.09 9.10 Jang MH, Shin MJ, Shin YB. Pulmonary and physical rehabilitation in critically ill patients. Acute and critical care. 2019 Feb;34(1):1. DOI: 10.4266/acc.2019.00444
  10. 10.00 10.01 10.02 10.03 10.04 10.05 10.06 10.07 10.08 10.09 10.10 10.11 10.12 10.13 10.14 10.15 10.16 10.17 10.18 10.19 10.20 Ahmad AM. Essentials of physiotherapy after thoracic surgery: What physiotherapists need to know. A narrative review. The Korean Journal of thoracic and cardiovascular surgery. 2018 Oct;51(5):293. DOI:10.5090/kjtcs.2018.51.5.293
  11. 11.00 11.01 11.02 11.03 11.04 11.05 11.06 11.07 11.08 11.09 11.10 11.11 11.12 11.13 11.14 11.15 11.16 11.17 Manocha S, Walley KR. Adjunctive Respiratory Therapy. IN: Vincent JL, Abraham E, Kochanek P, Moore FA, Fink MP. Textbook of Critical Care. 7th ed. Philadelphia: Elsevier; 2017.p.385-388 
  12. Alan N, Khorshid L. The effects of different positions on saturation and vital signs in patients. Nursing in critical care. 2021 Jan;26(1):28-34. DOI: 10.1111/nicc.12477
  13. 13.0 13.1 13.2 Kacmarek RM, Dimas S, Mack CW. Essentials of Respiratory Care-E-Book. Elsevier Health Sciences; 2013 Aug 13.
  14. 14.0 14.1 14.2 Pryor JA, Prasad AS. Physiotherapy for respiratory and cardiac problems: adults and paediatrics. Elsevier Health Sciences; 2008 Mar 6.
  15. PT Final Exam. Postural Drainage Lecture. Published 6 Aug 2018. Available from: [last accessed 10 May 2021]
  16. Tan Tock Seng Hospital. HVRSS 7. Chest Physiotherapy - Postural Drainage. Published 24 July 2019. Available from: [last accessed 10 May 2021]
  17. 17.0 17.1 17.2 Yadav N, Arora S, Kumari M, Yadav M, Sharma J. Knowledge and Awareness about Use of Manual Hyperinflation in ICU Patients Amongst Physiotherapy Students in Delhi NCR, India. International Journal of All Research Education and Scientific Methods. 2020 Nov;8(11).
  18. O’Donnell K. A survey of hyperinflation techniques in ICU based physiotherapists in the UK. Physiotherapy. 2019 Jan 1;105:e178. DOI:10.1016/
  19. 19.0 19.1 19.2 Heidari M, Shahbazi S. Nurses’ awareness about principles of airway suctioning. Journal of clinical and diagnostic research: JCDR. 2017 Aug;11(8):LC17.v DOI:10.7860/JCDR/2017/25550.10452
  20. 20.0 20.1 Hodgson CL, Tipping CJ. Physiotherapy management of intensive care unit-acquired weakness. Journal of physiotherapy. 2017 Jan 1;63(1):4-10. DOI:10.1016/j.jphys.2016.10.011
  21. Padula CA, Yeaw E. Inspiratory muscle training: integrative review of use in conditions other than COPD. Research and theory for nursing practice. 2007 Jun 1;21(2):98-118. DOI:10.1891/088971807780852039