Tag: ventilation

  • Video – Burns: The Practical Stuff

    Video – Burns: The Practical Stuff

    Uploaded to YouTube in April 2019; Filmed 2018

    Content warning: This video may contain sensitive content.

    This video demonstrates the assessment and management of burns, using equipment that is recommended within the locality at the time of production. Remember to check your local, current guidelines before putting anything into practice. Produced by HCPs and students.

    This video demonstrates use of burn gel wraps, which may no longer be used in your ambulance Trust. Please check your local guidelines regarding this. According to the British Burn Association:

    Burn gel wraps may be used to provide analgesia, but only after adequate cooling has
    occurred as they do not actively remove heat from the wound

    Varley et al (2014)

    Remember to follow good IPC in real life.

    The transcript below has been slightly edited, with titles added, to make it easier to read.

    Further recommended reading: The British Burn Association First Aid Clinical Practice Guidelines

    Transcript

    You must read the full disclaimer at www.article999.co.uk/disclaimer and check your local guidelines before putting into practice any of our content.

    BURNS: The practical stuff

    This video contains content some might find sensitive.

    Treatment

    With all assessments and interventions, use an aseptic technique, especially because ‘burns are prone to infection’

    Purcell, 2003: 217

    Airway

    The patient’s airway might worsen. Here’s why:

    ‘A burned patient may have a patent airway on the initial evaluation. […] In the time that follows, the face, as well as the airway, will likely swell.’

    NAEMT, 2016: 411

    … So, consider HEMS for RSI.

    Breathing

    The patient’s breathing might worsen. Here’s why:

    Is there a chest wall burn?

    ‘Burns constrict the chest wall similarly to having several leather belts progressively tightening around the patient’s chest. As time progresses, the patient cannot move the chest wall to breathe.’

    NAEMT, 2016: 412

    So, consider HEMS and ventilatory support where needed.

    Other considerations:

    Inhaled toxins ‘can produce asphyxiation’

    NAEMT, 2016: 412

    If:
    – LOC in a fire with ‘heavy smoke’
    – trapped patient in a fire
    consider O2

    El-Helbawy & Ghareeb, 2011

    Circulation

    Swelling might get worse. Here’s what to do about it:

    ‘Distal limb perfusion may be critically reduced’; ‘Burned extremities should be elevated during transport to reduce the degree of swelling in the affected limb’

    NAEMT, 2016: 412

    A complication of swelling:

    Fluid loss occurs from swelling and evaporation

    NAEMT, 2016: 416

    Giving Fluids – Pros and Cons

    Consider IV fluids, especially if the burn is >10% of the body (AACE, 2016: 265-266). Keep watching for info on how to determine this.

    Give fluids with caution. Too much -> ‘cardiac failure, […] infectious complications, acute respiratory distress syndrome, and even death’.

    Too little -> ‘hypovolemic shock, organ failure’

    (NICE, 2016)

    Judicious fluid management of children with severe burn injury can improve the respiratory outcome measures of these children

    Duran and Sheridan, 2016

    Cannulating – Essentials

    When cannulating, ‘placement through the burn is appropriate [only] if no alternative sites are available’

    NAEMT, 2016: 412

    What about heat?

    Patients with burns are not able to maintain their own body heat

    NAEMT, 2016: 413

    …So, give blankets

    ECGs

    ECGs are required for electrical burns (AACE, 2016: 265) but consider them for all burns as ‘cardiac dysrhythmias’ result from the release of ‘muscle potassium’ (NAEMT, 2016: 418) and studies have shown disturbances in the cardiac functions of in-hospital burn patients (Jeschke et al, 2008).

    Disability

    Do your BMs

    Hyperglycemia may occur in burns patients and has a higher risk of ‘morbidity and mortality in critically ill patients’ (Wolfe et al, 1979; Mecott et al, 2010).

    Pain management in children

    In children, ‘a multi-modal approach to pain and sedation can improve the neurological status of severely burned children’

    Duran and Sheridan, 2016

    Expose/Examine

    Cooling the burn:

    Cool with a wet compress

    Purcell, 2003: 217

    ‘Cooling gels such as Burnshield are often used by paramedics. These are useful in cooling the burn and relieving pain in the initial stages.’ *

    Be aware of the risk of ‘heat loss’

    Hudspith and Rayatt, 2004

    *This guidance is changing. Check your local guidance first, and consider the use of cling-film after running water.

    Documentation during examination:

    Assess and document:

    ‘Burn depth & features’ (Purcell, 2003: 217)

    Other considerations:

    Anticipate Swelling. Take off jewelry. Be aware that these and clothing ‘retain residual heat’ (NAEMT, 2016: 413).

    Cooling – more details

    Irrigate early to cool and prevent further burning.

    Chemical burns: 15 mins min (AACE, 2016: 265)

    All burns: Max 20 mins (AACE, 2016: 266)

    This is most effective ‘within 20 minutes of the injury’ (Hudspith and Rayatt, 2004).

    Don’t use ice cold water as ‘intense vasoconstriction can cause burn progression’ (Hudspith and Rayatt, 2004).

    When using cling film

    Discard ‘the first few centimetres’ to be aseptic

    ‘lay this on the wound rather than wrapping the burn’ to anticipate swelling

    (Hudspith and Rayatt, 2004)

    Consider using wet dressings instead in chemical burns (Allison and Porter, 2004)

    Estimating total burns

    Consider the use of tools to estimate the total body percentage of the burns (NICE, 2016; Mersey Burns, 2013).

    Transport

    Using those tools [such as Mersey Burns] will help determine the right treatment centre for the patient and the treatment priority.

    Time critical features:

    • major abcd problems
    • airway burns
    • history of hot air or gas inhalation
    • respiratory distress
    • burns that completely encircle the chest, neck, or limb
    • significant facial burns
    • burns >10% total body area
    • ‘presence of other major injuries’

    (AACE, 2016: 266)

    References

    Association of Chief Ambulance Executives (AACE), 2016. UK Ambulance Services Clinical Practice Guidelines. Bridgwater: Class Professional Publishing

    Allison, K. and Porter, K. 2004. Consensus on the prehospital approach to pain management. Emergency Medicine Journal. 21 (1), pp. 112-114

    Duran, C. and Sheridan, R.L. 2016. Current Concepts in the Medical Management of the Pediatric Burn Patient. Current Trauma Reports. 2 (4), pp. 202-209

    El-Helbawy, R.H. and Ghareeb, F.M. 2011. Inhalation injury as a prognostic factor for mortality in burns patients. Annals of Burns and Fire Disasters. 24 (2), pp.82-88

    Hudspith, J. and Rayatt, S. 2004. First aid and treatment of minor burns. BMJ. 328 (7454), pp. 1487-1489

    Jeschke, M.G. et al. 2008. Pathophysiologic response to severe burn injury. Anals of surgery. 126, pp. 37-51

    National Association of Emergency Medical Technicians (NAEMT). 2016. PHTLS. Prehospital Trauma Life Support, 8th Edition. Burlington: Jones and Bartlett Learning.

    NICE, 2016. Mersey Burns for calculating fluid resuscitation volume when managing burns. Available at: https://www.nice.org.uk/advice/mib58/chapter/summary (Accessed 06/04/19)

    Purcell, D. 2003. Minor Injuries. A Clinical Guide. Edinburgh. Elsevier.

    St Helens and Knowsley Teaching Hospitals NHS Trust, 2013. Mersey Burns. Available at: https://merseyburns.com (Accessed 06/04/19)

    *Stiles, K. and Goodwin, N. 2018. British Burn Association: First Aid Clinical Practice Guidelines. Available Online: https://www.britishburnassociation.org/wp-content/uploads/2017/06/BBA-First-Aid-Guideline-24.9.18.pdf (Accessed 29/03/21)

    *Varley, A. et al. 2014. British Burn Association: First Aid Position Statement. Available Online: https://www.nbt.nhs.uk/sites/default/files/attachments/British%20Burn%20Association%20First%20Aid%20Position%20Statement.pdf (Accessed 29/03/21)

    Wolfe, R.R. et al. 1979. Glucose metabolism in severely burned patients. Metabolism. 28 (10), pp. 1031-1039

    *Added to post 29/03/21

  • Ventilators: How?

    Ventilators: How?

    A shorter version of Ventilators: Why, What, How, When? featuring how-to use the ventilator demonstrations only. Made by UK Paramedics, this demonstrates how to use the PneuPac ParaPac ventilator.

    Read more:

    Ventilators: Why, What, How, When?

    How do I get the ventilator off the racks?

    What is the relief pressure dial on the ventilator?

    The Discovery of Negative and Positive Pressure Ventilation – Fast Fact

    What is positive pressure breathing?

    What is Negative Pressure Breathing?

    Disclaimer

    You must read the full disclaimer at www.article999.co.uk/about/ (disclaimer tab) before putting into place anything you see here. Useful information is available in the text on this video, so if you only listen to the narration you will miss important facts. The ventilation settings mentioned in this video are what is recommended by Smiths Medical, current guidelines and some articles – however, as with all topics, there is always varying information available online & alternative expert advice, and no video can cater for all of that. Similarly, this video is intended to demonstrate how to use equipment & to introduce or remind you to the Why, What and When of ventilators – not to tell you that you should or shouldn’t be using it. That is dependent on local guidelines, your research & your choice as a clinician. This video merely highlights the varying advice regarding tidal volume settings, and in the text points out the potential problems with some of the figures. No specific volume is recommended.


    Transcript

    Article 999. Ventilators: Why, What, How, When?

    This video has been made by UK Paramedics following guidelines. It is not endorsed by any author, organisation or Ambulance Trust. You must read the full disclaimer at www.article999.co.uk/about/ and refer to your local guidelines before putting into place anything you see here. This video is intended to demonstrate how to use the ventilator according to use guides and guidelines – not to tell you that you should or shouldn’t use it. That decision is up to you and should be dependent on local guidelines and your own research. This is what the textbooks, the manufacturer and a few articles say & is not intended to represent the expert opinions or experience of others within healthcare.

    Remember hand hygiene, bare below the elbows and gloves in real life.

     

     

    How?

    1. To remove the ventilator from the racks, pull the flap to the side and push the ventilator up. To put it back in, simply push it down and pull the flap to the side again.
    2. To connect to the gas supply, push the hose into the socket and twist. It’s the same when connecting to a portable oxygen cylinder.
    3. When you turn it on, the ventilator should complete a self check. The alarm lights should flash in sequence, there should be one burst of the high pressure audible alarm, and the orange indicator should flash for 60 seconds.
    4. Next, check the indicator shows white for O2.
    5. Connect the patient circuit [shown in video].
    6. Next on the list, adjust the ventilation parameters. Set the air mix control to no air mix for respiratory arrest or CPR. Set the relief pressure control to 40. Set the respiratory rate to 12. As for the tidal volume, it varies massively as you can see on the screen. It depends on whether you opt for an average value or base it on the patient’s weight. Smiths Medical (2017) advise 800-900ml on their training video, [but this may not be advisable] but don’t worry too much about the slight differences in tidal volume because the PneuPac features a high pressure alarm that we’ll discuss shortly. The alarm will help you identify if the tidal volume is too high for your patient.

    (Gregory & Mursell, 2010: 44; Pilbery & Lethbridge, 2016: 189; Baker, 2012; Smiths Medical, 2017)

    The following demonstrate the variance in researched texts and guidelines – not necessarily the advised settings:

    400-600ml Baskett, 1996
    500-600ml Perkins et al, 2015
    600ml Baker, 2016
    800-900ml Smiths Medical, 2017 – may not be advisable due to risks of barotrauma. See below
    6-8ml/kg Bocklage & Balk, 2017; Frakes, 2007
    10ml/kg or 5-8ml/kg Baker, 2012 – depending on the extent of the risk of barotrauma

    7. Next, temporarily occlude the patient connection. The relief pressure monitor should go to the maximum setting – i.e. 40cmh20.

    (Gregory & Mursell, 2010: 44; Pilbery & Lethbridge, 2016: 189; Baker, 2012; Smiths Medical, 2017)

     

    What do the audible warnings mean?

    • Top left is the high pressure alarm
    • Top right is low pressure
    • Bottom left is the battery indicator
    • The middle one tells you when breathing is detected by the ventilator

    (Smiths Medical, 2017)

    High pressure = excessive tidal volume, incorrect airway position, kinked ET tube, or incorrect ventilation settings.
    If the pressure is reaching it’s max, there may be something wrong with the circuit.

    If you’ve checked the above and the alarm is still sounding, Smiths Medical (2017) advise that your tidal volume setting might simply be too high.

    Low pressure = leakage or insufficient tidal volume/settings, faulty valve in the patient’s circuit
    This alarm tends to occur when pressure drops below 10cmh20

    Earlier, I pointed out the alarm in the middle, at the bottom. This is SMMV. It’s an indicator that will flash green if the patient is breathing for themselves. The ventilator will assist if the patient breathes with less than 150ml of tidal volume. Between 150-400ml the ventilator will extent the exhalation time to allow the patient to complete their own breath, and above 400ml the ventilator will allow the patient to breathe and will not assist, but may still assist on the next breath if required (Smiths Medical, 2017; Baker, 2012).

     

    Extra facts:

    McCarty et al (2012) found that ‘ventilation rates and tidal volumes commonly exceeded Guideline recommendations. This resulted in […] excessive mean airway pressure’

    Smiths Medical (2017) advise that peak inflation pressure should be below 20cmh20 when using a mask to ventilate due to the issues of too high pressure

    Inspiration to Expiration should be 1:2 (Smiths Medical, 2017; Baker, 2012)

    References

    Baker, D. 2012. Emergency and Transport Ventilation, an introductory guide, Smiths Medical International Limited: Luton

    Baker, D.J. 2016. Artificial Ventilation: A Basic Clinical Guide. Springer International: Switzerland

    Baskett, P. et al. 1996. ‘Tidal volumes which are perceived to be adequate for resuscitation’, Resuscitation, 31 (3), pp. 231-4

    Bocklage, T. & Balk, R.A. 2017. Setting the Tidal Volume In Adults Receiving Mechanical Ventilation: Lessons

    Learned From Recent Investigations, Available Online: https://www.nbrc.org/wp-content/uploads/2017/07/Setting-the-Tidal-Volume.pdf (Accessed 17/12/17)

    Frakes, M. 2007. Ventilation Modes and Monitoring, Available Online: http://www.rtmagazine.com/2007/02/ventilation-modes-and-monitoring/ (Accessed 17/12/17)

    Gregory, P. and Mursell, I. 2010. Manual of Clinical Paramedic Procedures, West Sussex: John Wiley & Sons

    McCarty, K. et al, 2012. Ventilation rates and tidal volume during emergency department cardiac resuscitation, Resuscitation, 83: 4, p45

    Owen, R. and Castle, M. 2006. ‘EtCO2: the key to effective prehospital ventilation’, Emergency Medical Journal, 23 (7), pp. 578-579

    Perkins, G.D. 2015. European Resuscitation Council Guidelines for Resuscitation 2015: Section 2. Adult basic life support and automated external defibrillation, Available Online: https://ercguidelines.elsevierresource.com/european-resuscitation-council-guidelines-resuscitation-2015-section-2-adult-basic-life-support-and/fulltext#back-bib0760 (Accessed 17/12/17)

    Pilbery, R. & Lethbridge, K. 2016. Ambulance Care Practice, Bridgwater: Class Professional Publishing

    Smiths Medical, 2017. ‘Pneupac – ParaPAC’, Pneupac Transport Ventilators – Breathe Easy, Available Online: https://www.smiths-medical.com/resources/pneupac-transport–ventilators—breathe-easy (Accessed 27/10/17)

    With thanks to Smiths Medical for their correspondence and information

    Music:
    Dobroide, 2010. 20091229.ambulance.siren.wav. Available Online: https://freesound.org/people/dobroide/sounds/8713/ (Accessed 21/08/17)

    Productiontrax.com

    Images:

    Article 999’s own or licenses purchased via Adobe Stock & Dreamstime


    Feedback is welcome & responded to. Stay tuned for more content!

     

    Displayed on one of our ‘Fast Facts’ pages. Click on the image for the link & reference!

     

  • What is the relief pressure dial on the ventilator?

    What is the relief pressure dial on the ventilator?

     This article refers to the workings of Smith’s Medical Pneupac ParaPac and the newer ParaPac Plus. Other transport ventilators may vary in their settings and processes. Please check what unit your ambulance trust has before following the information here.

     

    [tabby title=”Detail”]

    The pressure of air inside our lungs is normally just right to not only ensure that negative pressure breathing occurs but also to prevent a shunt (where blood bypasses the lungs) (Hess & Kackmarek, 2014: 431), the oesophageal spinchter from opening, causing air to enter the stomach (Baker, 2012: 1), and a host of other potential problems. Any means of supported ventilation where the patient is not breathing for themselves produces positive pressure ventilation. Not only does this change the way air enters the patient’s lungs while they are ventilated, but it also comes with all of the above risks if any of the settings are incorrect, and more.

    Many of the effects ‘are related to mean airway pressure [which is] […] the average pressure applied to the airway during the ventilatory cycle’ (Hess & Kackmarek, 2014: 420) With too ⇑ pressure comes ⇓ venous return (Hess & Kackmarek, 2014: 420) and ⇑ chance of barotrauma (Baker, 2016: 75).

    To summarise, the potential negative effects are:

    • Blood bypassing the lungs (a shunt) (Hess & Kackmarek, 2014: 431)
    • Air entering the stomach (Baker, 2012: 1)
    • Venous return decreasing (Hess & Kackmarek, 2014: 420)
    • Barotrauma (Baker, 2016: 75)

    Because modern ventilators are volume-controlled, preventing a different problem that occurs during pressure-controlled ventilation, there is a set tidal volume which the ventilator will always provide to the patient. To provide this volume, the pressure will constantly increase until the volume is reached (Baker, 2016: 132).

    The Means of Avoiding These Problems

    In ventilators, the pressure of an oxygen cylinder ‘is lowered through a reducing valve down to 30-90psi’ from 2000psi. It’s then delivered to the patient ‘to a maximum of 40cmh20 or 60cmh20’, (Baker, 2012: 18)*, depending on whether you’re in the UK or the US.

    *cmh20 = centimetres of water pressure (SensorsONE, 2017)

    Since we can’t have too much pressure there needs to be a way of stopping the ventilator if things get awry. The relief pressure is what this refers to. Via a safety valve (Baker, 2012), otherwise known as ‘exhaust valves’ the supply is cut and excess peak inspiratory pressure (PIP) is released into the atmosphere (Zaconeta et al, 2010), ‘prevent[ing] over-ventilation of the lungs’ (Baker, 2016: 145)

    Why would the pressure get this high anyway?

    • ‘The patient circuit […] [could be] blocked or kinked’ (Baker, 2016: 142). Best to check it.
    • ‘If the lung compliance[*] is low and the airway resistance is high the pressure can rise to high levels’ because, as above, the pressure will keep rising until the set tidal volume is delivered (Baker, 2016: 142).
    • The wrong relief pressure settings.

    *Compliance ‘refers to the ease of expansion of the lungs and the walls of the thorax’ (Baker, 2012: 8). Ordinarily, according to Baker (2012: 8), the value is 100 cmh20 but when ventilated it’s 40-50cmh20. Physical injuries and medical conditions may further alter this figure.

    Which dial are you talking about?

    This one

    The Pneupac ParaPac (Smiths Medical). Photo highlights the Relief Pressure dial.

    What should I set it to?

    40cmh20 if you’re in the UK (Baker, 2012)

    Why is the relief pressure set at 40cmh20 in the UK? Why is it 60cmh20 in the US?

    Article 999 is struggling to find the answers to these questions. If you know the answers, please get it touch. It would be great to add the information to this resource.

    This post is yet to be peer reviewed. Please get in touch if you have any comments.

     

    [tabby title=”Super Summary”]

    Article 999 previously posted an article on positive pressure ventilation, including its risks. The aim of positive pressure ventilation is to ‘maximise the potential benefit of mechanical ventilation while minimizing the potential for harm’ (Hess & Kackmarek, 2014: 407). The relief pressure dial on the ventilator ensures that the pressure of ventilation is not so high as to cause blood bypassing the lungs (Hess & Kackmarek, 2014: 407), the oesophageal spinchter opening (Baker, 2012: 1), barotrauma (Baker, 2016: 75; Hess & Kackmarek, 2014) and more. The ventilator’s other settings ensure that the patient actually receives ventilation, but the relief pressure setting ensures that a valve drains excess air when settings, poor setup, or the patient’s lung compliance (Baker, 2016: 43) have caused the pressure to get to high.

    What should I set it to?

    40cmh20 (Baker, 2012)

    What should I look out for if the pressure is too high?

    Kinked tubing (Baker, 2016: 142) & your settings

    Read more in the Detail tab.

    [tabby title=”Prefer to see a diagram? Check out the mind-map summary”]

     

    [tabby title=”References”]

    References

    Baker, D. 2012. Emergency and Transport Ventilation, an introductory guide, Smiths Medical International Limited: Luton

    Baker, D.J. 2016. Artificial Ventilation: A Basic Clinical Guide. Springer International: Switzerland

    Hess, D.R. & Kacmarek, R.M. 2014. Essentials of Mechanical Ventilation. McGraw Hill Education: New York

    SensorsONE, 2017. cmh20 – Centimetres of Water Column at 4 deg C Pressure Unit, Available Online: https://www.sensorsone.com/cmh2o-centimetres-water-column-4-deg-c-pressure-unit/ (Accessed 16/11/17)

    Zaconeta, C.A.M. et al, 2010. ‘Evaluation of peak inspiratory pressure and respiratory rate during ventilation of a preterm infant lung model with a self-inflating bag by paramedics of the Fire Department’, Revista Paulista de Pediatria, vol. 28. No. 1.

    Not endorsed by but with thanks to Smiths Medical for providing information.

    [tabbyending]

     

  • The Discovery of Negative and Positive Pressure Ventilation – Fast Fact

    The Discovery of Negative and Positive Pressure Ventilation – Fast Fact

     

    ‘He opened the chest of a live animal and noted that air rushed in and the lungs collapsed, following which the heart stopped’ (Baker, 2016: 3).

    His experiment was actually repeated in 1667 by one Robert Hooke. He used positive pressure ventilation to keep a dog, whose chest had been opened, alive. This was ‘the first demonstration that it was the gas entering and leaving the lungs which supported life and not the movement of the lungs themselves’ (Baker, 2016: 3-4).

    This was one of many discoveries that birthed the idea of positive pressure ventilation, the understanding of negative pressure ventilation and the various forms of artificial ventilation that followed.

     

    Reference

    Baker, D. J. 2016. Artificial Ventilation: A Basic Clinical Guide, Springer International: Switzerland.

  • What is Negative Pressure Breathing?

    What is Negative Pressure Breathing?

    Negative pressure breathing is how we breathe normally, without the aid of bag-valve-masks or mechanical ventilators.

    Inspiration – Normally

    Breathing in is produced by ‘contraction and downward motion of the diaphragm [which] causes a negative pressure in the chest’ —–> inspiration. (Goldberg, 2014: 51, emphasis added)

    Inspiration is therefore a muscular process (the diaphragm is a muscle) which is normally mainly reliant on the diaphragm. However, accessory muscles including the ‘pectoralis major and minor’ may also be used and are ‘vital to survive in certain pulmonary conditions’ (Goldberg, 2014: 51).

    Let’s explain this by breaking it down:

    Why does a contracting diaphragm cause negative chest pressure?

    Because the volume has increased. This process is represented in Boyle’s Law (Rice University, 2016). Put simply, more space = more volume. When there’s more space in the chest, as with the contracting diaphragm, there is more room for air particles to move. They’re not crammed in any more, so there’s not much pressure.

    On the other hand, when those air particles are tightly squeezed in a smaller space, there is less pressure.

    To summarise:

    • more space = more volume
    • less space = less volume
    • more volume = less pressure
    • less volume = more pressure
    • Tightly squeezed particles in little volume cause a lot of pressure
    • Free moving particles in a lot of volume cause less pressure

    Why does negative pressure cause inspiration?

    This has to do with the laws of thermodynamics. ‘For anything to happen, energy has to move or flow or change’ and ‘energy has an absolute unfailing tendency to go from “more concentrated” to “less concentrated”‘ (Watson, 2014).

    So, it’s not so much because there is a negative pressure that we inhale. It’s because there is a change in pressure. When the diaphragm contracts, the pressure changes from high to low. Now there is no equilibrium. One of the laws of the universe (which is called a law because it’s been observed over and over again in different ways) occurs as a result: energy attempts to shift toward equilibrium. And the way it does that is by moving from an area of high pressure (outside the body) to one of low pressure (inside us).

    Watson, 2014 has written a great explanation of this here: http://www.ftexploring.com/energy/2nd_Law.html>

    Also, this is a great video which demonstrates the process: https://www.youtube.com/watch?v=q6-oyxnkZC0

    Expiration – Normally

    pexels-photo-321576

    This is ‘largely passive’, frequently happening ‘without any muscle action’ when relaxed. The contracted diaphragm simply ‘springs back into shape’ (Goldberg, 2014: 51). However, using the ‘external and internal intercostal muscles’ amongst others, you can ‘voluntarily exhale forcefully’ (Goldberg, 2014: 51).

    Either way, this process creates more pressure because there is now less volume (less space) for air particles to move around. Following the laws described above, air moves from an area of high pressure (the lungs) to an area of low pressure (outside) (Collison et al, 2002: 57; Watson, 2014).

    It’s intuitive that this change in pressure and lack of equilibrium (Watson, 2014) will ensure that the process repeats itself. Each time the diaphragm contracts, the volume changes so the pressure changes. Air flows inside. Then there’s too much pressure and less volume as the diaphragm is returning to shape (Goldberg, 2014). So air flows out. Then the diaphragm contracts again…

    References

    Baker, D. n.d. Emergency and Transport Ventilation: an introductory guide, Smiths Medical International Limited: Bedfordshire

    Collison, P. et al, 2002. Nelson Modular Science: 2, Nelson Thornes Ltd: Cheltenham.

    Goldberg, S. 2014. Clinical Physiology made ridiculously simple, MedMaster: Miami.

    Rice University, 2016. The Process of Breathing, Available Online: https://opentextbc.ca/anatomyandphysiology/chapter/22-3-the-process-of-breathing/ (Accessed 01/11/2017)

    Watson, D. 2010. The Second Law of Thermodynamics, Available Online: http://www.ftexploring.com/energy/2nd_Law.html (Accessed 01/11/2017)


    This article has not been endorsed by any company.

    With thanks to Smiths Medical for providing information.


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    This post is yet to be peer reviewed. Please get in touch if you have any comments.