Category: Nice to know

On-Water Rescue Breaths for Divers – Worth it?
For clarity, the term ‘in-water rescue breaths’ has been replaced with ‘on-water rescue breaths’ as these are given on the water surface.

Drowning Vs Diving

When we talk about the diving casualty, we don’t just mean a drowned patient. Any drowned patient may have some other medical cause to explain why they drowned in the first place – a cardiac or neurological cause, for example – and the same is true for the diving patient. But in diving, we may not mean drowned at all, not in the traditional sense. If a patient has managed to keep their regulator in for the entire ascent, and that regulator is working properly, have they drowned? Or is the bigger issue the subsequent decompression illness from not breathing on ascent, and immersion pulmonary oedema?

Let’s have a look at the guidelines for the management of a drowned casualty.

UK Guidelines and First Aid

Most first-aiders will know the drowning protocol:
- 5 initial rescue breaths
- 30:2 CPR
In the 2021 UK Resus Council guidelines, this hasn’t changed, but there is a bullet point that reads:

Start resuscitation as soon as safe and practical to do so. If trained and able this might include initiating ventilations whilst still in the water or providing ventilations and chest compressions on a boat.
Start resuscitation by giving 5 rescue breaths / ventilations using 100% inspired oxygen if available.
Deakin et al (2021)

European Guidelines

What’s interesting is when you then look at the European Resus Council Guidelines 2021. Here, you’ll find much more detail under the drowning section, including the background research that has informed the guidelines. Of note, there is ‘limited evidence […] to inform the treatment of the drowning victim’ (Lott et al, 2021: 197). Despite this, a table of research includes evidence on in-water resuscitation. Four main points are raised:
- Rescue breaths ‘by highly trained rescue teams with water rescue equipment is feasible’
- These breaths should be given for ‘up to 1 min’ (emphasis added) (10 breaths) ‘before attempting transfer to land’
- No further rescue breaths should be given before landing the patient on land or on the boat
- If a rescuer is alone and has no rescue equipment, they should not begin rescue breaths and should instead tow ‘directly to the shore’ or boat (emphasis added).
(Lott et al, 2021: 199).

Why 10 breaths? This should equate to one every 6 seconds, which is exactly what we would do during continuous CPR with an advanced airway, or during ventilation-only CPR in respiratory arrest (Newell, Grier, & Soar, 2018). (However, this paper highlights the potential for increased survival after 30:2 versus continuous CPR).

Note the difference in wording between the 2015 guidelines (below) and the 2021 guidelines (above):

If a rescuer, in general a surf-lifeguard, finds a non-responding drowning victim in deep open water, the rescuer may start ventilation when trained to do so before moving the victim to dry land or rescue craft. Some victims may respond to this.
Truhlář et al. (2015).

The 2015 guidelines leaned more towards in-water ventilations than the 2021 guidelines do. The wording was perhaps vague, and left the decision up to the rescuer for when to start ventilations and how long to perform them for, unless the patient was not responding to initial ventilations. In this case, the guidelines emphasised towing the patient to the boat or shore – if it was near – without further ventilations.

The 2021 guidelines, though clearer, do not detail what defines water rescue equipment, or what defines highly trained. Do rescue divers, who are trained at BLS level, constitute ‘highly trained’? Do lifeguards, who frequently practice water rescue, count as highly trained? Or is this term reserved for only ALS-trained healthcare professionals who are also trained in water rescue, or at minimum ILS-trained rescue divers? When we talk about rescue equipment do we mean use of bag-valve-masks and airway adjuncts? Does water rescue equipment include a BCD that is inflated? Translating this advice into diving medical advice is not easy.

British Sub-Aqua Club Guidelines – What Might Change?

BSAC provide dive rescue courses and teach on-water rescue breaths (Cumming, 2011: 56-57), however this information has yet to be updated to the 2021 Resus Council guidelines, and it will be interesting to see what changes when it is updated. The referenced book recommends ventilations while towing, which was not a feature of the 2015 ERC guidelines and makes this book less reliable as a source of information. On the contrary, their Sports Diver student guide (BSAC, 2020: 47), has been updated to stop the practice of giving rescue breaths while towing. Perhaps the biggest change in the next issue will be that a lone rescuer may not be advised to start ventilations in the water, unless help is coming to them and BCDs are considered rescue equipment. Rescuers should also be reminded that the Resus Council advise up to one minute of rescue breaths (Lott et al, 2021: 199). One other change that would be good to see would be a friendly reminder to not perform rescue breaths if this would cause a delay in transport and treatment of the patient – an exemption for some treatments that HCPs should be well versed in. An example of where this might apply would be where the time it takes to give rescue breaths is longer than the time it would take to evacuate this patient to the shore or a nearby boat.

UKDMC – Are Times Changing?

This statement from the UKDMC (Edge and Wilmshurst, n.d.) states that there is a higher chance of neurological damage, despite an apparent improvement in survival rates, when on-water resuscitation is performed. Remind anyone of the trial results from something else we do in resus? They also note that even when lifeguards are performing in-water ventilations, the patient aspirates, and the rescuer tires. And this was in a pool… Now imagine waves of salty water lapping over both patient and rescuer. Multiple other issues arise – ventilation may be restricted by diving equipment that covers the chest, rescuers will be unable to assess chest rise and fall due to this equipment, and even those of us who are HCPs won’t have regular practice, especially in the special circumstances of resus of diving patients.

This doesn’t even consider that in the absence of pulse checks (due to wet/dry suits covering the neck), the rescuer is unable to assess respiratory versus cardiac arrest, and may be at risk of confirmation bias – that casualty who was in cardiac arrest when they surfaced, they have a pulse on the boat so we must have got them back, right? Or, that unconscious patient who wasn’t breathing is breathing now, so we saved them – or were they just breathing so shallow that, in amongst the noise of the boats and the waves, and with all that equipment on them, we could not look, or listen, or feel. Realistically, this may be one reason there is limited evidence. It will be interesting to see how diving organisations respond in the future and whether their guidelines continue to change.

References

British Sub-Aqua Club, 2020. Sports Diver: Student Guide. BSAC.

Cumming, B. 2011. Safety and Rescue for Divers, BSAC: Cheshire.

Deakin, C.D. et al (2021) Special Circumstances Guidelines. Available at: https://www.resus.org.uk/library/2021-resuscitation-guidelines/special-circumstances-guidelines (Accessed 11/12/2021).

Edge, C. And Wilmshurst, P. n.d. The Rescue of a Diving Casualty – A Discussion Paper. Available at: https://www.ukdmc.org/wp-content/uploads/2017/04/PW-and-CJE-position-paper-on-diver-rescue.pdf (Accessed 11/12/2021).

Lott, C. et al (2021) ‘European Resuscitation Council Guidelines 2021: Cardiac arrest in special circumstances’, Resuscitation, 161, pp: 152-219. Available at: https://cprguidelines.eu/assets/guidelines/European-Resuscitation-Council-Guidelines-2021-Ca.pdf (Accessed 11/12/2021)

Newell, C. Grier, S. And Soar, J. (2018) ‘Airway and ventilation management during cardiopulmonary resuscitation and after successful resuscitation’, Critical Care, 22(190). doi: https://doi.org/10.1186/s13054-018-2121-y

Truhlář, A. et al (2021) European Resuscitation Council Guidelines for Resuscitation 2015: Section 4. Cardiac arrest in special circumstances. Available at: https://ercguidelines.elsevierresource.com/european-resuscitation-council-guidelines-resuscitation-2015-section-4-cardiac-arrest-special#BSPECIALENVIRONMENTS (Accessed 11/12/2021)
December 11, 2021
When Treating Burns, Consider IV Fluid

This is a fast fact based on this post. Full reference available there.

April 5, 2021
Should Patients Take Caffeine-Containing Analgesics?

Many of our patients have high temperatures, especially during COVID outbreaks. Some of them are taking over the counter pain relief as required. This is of course recommended, however many of our patients are also tachycardic due at least in part to their high temperatures. When they complain of palpitations, do they need to be aware of the effects of caffeine-paracetamol combinations? Should they be taking this combination at all, or should they simply ease off dietary sources of caffeine while taking analgesics? Here are a few quotes on the subject for discussion. Full references are below. For a fast fact summary, have a look at the featured image below:

A dose of caffeine equivalent to a mug of coffee added to a standard dose of common analgesics such as paracetamol or ibuprofen provided better pain relief. Analgesic plus caffeine increased the number of people who had a good level of pain relief by 5% to 10% compared with analgesic alone
Derry et al, 2014.

But…

When the recommended paracetamol-caffeine dosing regimen is combined with dietary caffeine intake, the resulting higher dose of caffeine may increase the potential for caffeine-related adverse effects such as insomnia, restlessness, anxiety, irritability, headaches, gastrointestinal disturbances and palpitations.
EMC, 2017

Even a small dose of 50 mg caffeine can cause tachycardia, anxiety and ectopic beats. Toxicity is normally seen at doses > 500 mg, but this depends on tolerance.
Take into account dietary and other medicinal sources of caffeine: people may not be aware from the brand name that a particular preparation contains caffeine. Consider whether paracetamol with caffeine is necessary: it cannot be assumed that it will be tolerated in the same way as paracetamol alone.
NPS MedicineWise, 2010

References

Derry, C.J. et al, 2014. Caffeine as an analgesic adjuvant for acute pain in adults. [online] Available at: https://www.cochrane.org/CD009281/SYMPT_caffeine-analgesic-adjuvant-acute-pain-adults (Accessed 21/01/21)

EMC, 2017. Paracetamol & Caffeine 500/65 mg Effervescent Tablets. [online] Available at: https://www.medicines.org.uk/emc/product/7416/smpc#gref (Accessed 21/01/21)

NPS MedicineWise, 2010. Paracetamol with caffeine (Panadol Extra) available over the counter from pharmacies. [online] Available at: https://www.nps.org.au/radar/articles/paracetamol-with-caffeine-panadol-extra-available-over-the-counter-from-pharmacies (Accessed 21/01/21)

January 22, 2021
What is the structure of the digestive system?
A Biology (basics) post.
‘The human digestive system consists of the alimentary canal [the gut] and its associated glands, the salivary glands, the liver and the pancreas. The alimentary canal begins at the mouth and ends at the anus. Between the two openings is a long convoluted tube organised into several distinct regions.’
(Boyle and Senior, 2008: 131).

The Short Answer

The digestive system is:

the ‘alimentary canal and its associated glands, the salivary glands, the liver and the pancreas.’ (Boyle and Senior, 2008: 131)

The Extended Answer

Within the alimentary canal are:

The mouth, including the tongue and teeth.
The oesophagus, which ‘carries food from the mouth to the stomach’
The stomach, ‘a muscular bag or sac that stores food’
The small intestine, which is where most digestion and absorption occurs. It includes the:
duodenum
ileum
The large intestine, including the:
appendix
colon, ‘whose main function is to absorb water’
rectum
The anus

(Boyle and Senior, 2008: 130-131)

The digestive system is therefore consisted of all of the above as well as the liver ‘and its adjuncts – the gallbladder and bile ducts’ (Keeton et al, 2020), pancreas, and the salivary glands.

Of course, each component has its own functions and parts. As such, this answer could be extended even further.

References

Boyle, M. And Senior, K. 2008. Human Biology, Third Edition, Collins: London

Collison, P. et al, 2001. Nelson Modular Science 1, Nelson Thornes: Cheltenham

Keeton, W.T. et al, 2020. Human Digestive System, Available Online: https://www.britannica.com/science/human-digestive-system (Accessed 13/09/20)
Digestive system with salivary glands (licensed Adobe image)
September 13, 2020
PARAMEDIC-2 Trial Results
‘For more than 50 years, treatment strategies have included the use of various drugs, but there is limited evidence that such treatments are effective’ (Perkins et al, 2018).

Now the PARAMEDIC-2 trial results are in…
- 8014 patients of the 10, 623 initially selected were included in the trial.
- Of these, 4015 were given adrenaline and 3999 a placebo.
- Of those who were given adrenaline and survived until discharge, 39 (31.0%) out of 126 patients had a ‘severe neurological impairment’ and of those who were given the placebo, the same was true for ’16 of 90 patients [17.8%]’
  (Perkins et al, 2018).
Exclusions to the trial
- ‘…those with anaphylaxis, pregnant women and children’ (below age 16).
- After the pilot, life-threatening asthma as a suspected cause of the cardiac arrest was added as an exclusion because of ‘the potential overlap between the presentation of asthma and anaphylaxis’.
- Anaphylaxis was excluded because adrenaline is considered potentially ‘beneficial’ for this condition
  (Warwick Clinical Trials Unit, 2018).
The trial only looked at the effects of the use of adrenaline during out-of-hospital cardiac arrest and not at the use of adrenaline during ROSC, which is a protocol that some Trusts follow (Warwick Clinical Trials Unit, 2018). In addition, this does not cover any treatment initiated by the hospital if the patient was transported there.

Conclusions

‘the benefits of epinephrine that were identified in our trial are small, since they would result in 1 extra survivor for every 112 patients treated. This number is less than the minimal clinically important difference that has been defined in previous studies.^29,30 Among the survivors, almost twice the number in the epinephrine group as in the placebo group had severe neurologic impairment’ (Perkins et al, 2018).

Limitations

Perceived limitations include: ‘Information about the quality of CPR was limited to the first 5 minutes of cardiac arrest and involved fewer than 5% of the enrolled patients.’ (Perkins et al, 2018)

Further limitations to consider could be:
- time to CPR
- patient’s co-morbitities that weren’t already considered in the study
More information

Warwick’s Clinical Trials Unit have produced an infographic with more information here.

View the University of Warwick’s press release here.

References

NIHR, 2018. Investigating the role of adrenaline in cardiac arrest. Available Online: https://www.nihr.ac.uk/news/investigating-the-role-of-adrenaline-in-cardiac-arrest/8931 (Accessed 19/07/18)

Perkins, G.D. et al, 2018. A randomized trial of epinephrine in out-of-hospital cardiac arrest. New England Journal of Medicine. doi: 10.1056/NEJMoa1806842

Warwick Clinical Trials Unit, 2018. Available Online: https://warwick.ac.uk/fac/med/research/ctu/trials/critical/paramedic2/faqs/ (Accessed 19/07/18)
July 19, 2018
What are the different methods of documentation?
In a 2010 study of nursing care in an Italian hospital, researchers found that just ‘40% of nursing activities observed were included in the nursing records’ (Marinis et al, 2010). Although this study was about nurses, not prehospital medics, it indicates the potential for missing key information in our documentation. A variety of models exist to help ensure that all the useful information is in your paperwork by the time it’s finalised & to ensure that it’s clear and concise…

Before the methods are introduced, make sure to note the following:
- There is not just one method
- Patient report forms vary across Trusts. Essential (required) criteria varies too.
- Policies regarding paperwork can be found publicly on most Trust websites and will be linked to from here if permission is gained.
- There is little freely available information regarding paramedic PCR completion in the UK. Each Trust has their own policy but those policies mainly centre around mandatory fields, not around how to structure your paperwork.
- Regardless of what you use, Gregory and Mursell’s (2010: 190) recommendations include ensuring it is ‘clear, accurate and legible [,] […] objective [and] […] first hand’. However, if your information is not first hand, they advise adding the ‘name and position’ of the person who gave you the information (2010: 190).
- What do I do if I make a mistake in my paperwork? (link coming soon)
There are 8 models of documentation for medical professionals
A few variations of these may exist where people have chosen to add a letter to the above acronyms to extend the models.

Doctors and websites regularly used by paramedics including Geeky Medics, seem to suggest a combination of the ABCDE, ROS & SOAP approaches, depending on the patient’s presentation (Geeky Medics, 2018).

Jump to discussion points

Jump to references

What is the ABCDE approach?

ABCDE approach

Simply, this involves transferring information from the DR ABCDE primary survey (Resuscitation Council, 2018) onto paper. Farrington (2018) mentions documenting this approach.

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What is the ROS approach?

Review of Systems Approach

The review of systems (RoS) approach is widely used and accepted in healthcare, and easily assimilates into paramedic practice. RoS improves patient care by holistically assessing the patient, and can make the inter-professional handover of a patient to another team more professionally acceptable. Documentation using the RoS is more comprehensive and less prone to errors. (Jenkins, 2013)

ROS is:
- Also known as the systematic enquiry (Douglas et al, 2013: 35)
- Recommended by Pilbery and Lethbridge (2010: 191) and forms the structure of the secondary surveys featured in Blaber and Harris (2011).
- Part of many models of documentation & not strictly a model on its own
- Involves writing a list of systems i.e. Respiratory, Cardiovascular, Central nervous, and listing examinations beneath each subsection. So, for a patient complaining of chest pain the ROS might show:
Cardiovascular

Weak radial pulse

Tachycardic: 95.

No added heart sounds

Pitting oedema

Respiratory

Equal chest movement. No deformities to chest
Bilateral crackles on auscultation

…and so on

(The Regents of the University of California, 2015; Snadden et al, 2013)
*Note these are just examples and are not intended to demonstrate a complete patient report form.

You do not have to review every system for every patient but you should review the ones that are ‘related’ to the presenting complaint or the primary affected system (Blaber and Harris, 2011: 22).

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Below is one suggested way to use ROS as part of a complete patient record form:

Presenting complaint – PC

History of Presenting Complaint – HPC

Past Medical History – PMH

Drug History – DH

Allergies

Family History – FH

Social History – SH

On Examination (O/E)

Review of Systems – ROS

Impression – IMP

Plan

(Gregory & Mursell, 2010: 191; Douglas et al, 2013: 32-39)

Variations of this model

The Douglas et al (2013: 32-39) model includes allergies in the drug history section, names review of systems as ‘systematic enquiry’, and includes the on examination section within that enquiry, rather than before it. They also add ‘information given’ to the patient and their relatives, and ‘progress notes’ to the model (Douglas et al, 2013: 39) to separate patient progress from the initial presentation & impression.

However, their model is not designed specifically for prehospital medics. Their example suggests the progress section should be used by Doctors who review patients at a later date. Gregory & Mursell’s (2010: 191) adaptation of this model is designed with Paramedics in mind. Still, a progress note section could be useful for prehospital documentation in situations where the patient’s condition changes in the relatively short time we spend with them. Following a structure which specifies documenting patient improvement or deterioration could help make our documentation clear. Comments? Add them below —>

Note, as mentioned above, that the ROS approach is part of a multitude of different approaches to writing paperwork. It is included in many of the following models either in documenting a patient’s past medical history (Beebe & Myers, 2010: 343-344) or in the secondary survey (Blaber and Harris, 2011), or both.

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What is the CHART approach?

CHART

CHART stands for:
- Chief complaint
- History
- Assessment
- Rx = Drugs
- Treatment
(Beebe & Myers, 2010: 342)

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What is CHARTIE?

This is the same as the above, with two additions:
- Intervention
- Evaluation
(Beebe & Myers, 2010: 342)

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What is the NAP approach?

This could be a good way to remember NAP

Nap stands for:
- Narrative (of the complaint)
- Assessment
- Plan of treatment
(Beebe & Myers, 2010: 342)

According to Beebe & Myers (2010), the three models listed above are now less frequently used, in favour of newer models like CHEATED.

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What is CHEATED?

CHEATED
- Chief concern
- History
  - Including the history of the complaint
  - Including ‘OPQRST (onset, provocation, quality of pain, radiation, severity, timing’ (Beebe & Myers, 2010: 342) where relevant
  - Including past medical history,
  - Including review of systems,
  - Including pertinent negatives.
  - Note that Beebe & Myers (2010) recommend using the review of systems structure in order to collect information about the patient’s past medical history. Other sources, including Douglas et al (2013) use the systematic enquiry/review of systems as part of the examination section.
  - Beebe & Myers (2010) include information in the history section of the CHEATED model that is more relevant for insurance-based healthcare systems. Only information relevant to UK medics has been included in this post.
- Examination of physical signs
- Assessment
  - Including the patient’s consent & any refusal of care
- Treatment
- Evaluation
  - ‘Following every treatment there should be an evaluation of the effectiveness of that treatment, or, at a minimum, a statement about the patient’s ongoing condition’ (Beebe & Myers, 2010: 346)
  - If the patient refuses care of transport, an ‘explanation of outcomes’ can be used here (Beebe & Myers, 2010: 346).
- Disposition
  - This is a summary of the patient & their treatment at the time of handover
  - Worsening advice if the patient has been left at home
(Beebe & Myers, 2010: 323-346)

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What is SOAP?

SOAP

SOAP stands for:
- Subjective
  - Patient’s feelings
  - Patient’s own words
  - Patient’s symptoms
- Objective
  - Signs
  - Clinical examination
- Assessment
  - Summary of symptoms & signs
  - Impression
- Plan
(Potter, 2018) – Geeky Medics

‘For the past 50 years, one of the primary organizing structures for physicians’ clinical documentation have been the SOAP note (Subjective, Objective, Assessment, Plan). The cognitive check list is well-suited to differential diagnosis but may not support detection of changes in systems and/or learning from cases.’ (Lenert, 2016)

There are several other variations of SOAP, including SNOCAMP, which adds the ‘nature of the presenting complaint, counseling, and medical decision making’ (Larimore & Jordan, 1995).

Lenert (2016) have concerns about the subjective section of the SOAP model & the potential for poor decision making due to its structure. Introducing OODA…

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What is OODA?

OODA
- Observe
- Orient, including Predictions = contextualising observations, including consideration of the patient’s wishes and/or needs, prioritising, considering guidelines, consider consequences & develop plans
- Decide
- Act, including Predictions = treatment & considerations of outcomes
‘there are cognitive models that outline steps that can help novices and experienced users maintain situational awareness and learn in rapidly changing environments. One such model, which was initially developed by Boyd to help Air Force pilots outthink their opponents in aerial combat but is now widely applied within the U.S. military, is the Observe Orient Decide Act (OODA) model.’ (Lenert, 2016)

OODA is:
- Designed to be ‘a repeating loop’ (Lenert, 2016)
- ‘action-oriented’ (Lenert, 2016)
- ‘allows […] reconsideration of assumptions’ (Lenert, 2016). Put simply, it reminds us to check and re-check
- recommended in the ‘subsequent management of patients’ where SOAP is useful in the initial approach to a patient (Lenert, 2016)
‘The goal of the OODA Loop is “think” and “act” faster and better than the enemy [.] […] Bad outcomes occur when medical treatments are not adjusted fast enough, based on current hypotheses about what the illness is, to outpace progression of the illness.’ (Lenert, 2016)

It may help with ‘situational awareness, and in detecting change and errors in diagnosis.’ It may also ‘improve communications by explicitly documenting a clinician’s reasoning and decisions, much of which is not transparent in SOAP notes.’ (Lenert, 2016)

However, it’s worth bearing in mind that neither SOAP nor OODA was originally designed for pre-hospital care.

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Considerations/Discussion Points
- Could OODA be used as part of a reflective framework? The model focuses on decision making and the key parts of patient assessment, which could become a reflective aid.
- Could OODA be used for time-critical patients?
- Could OODA be used as part of other models for when patients or situations become challenging or time-critical?
- E.g. a patient whose initial presentation is hypoglycaemia, who requires quick decision making but may then become stable
- e.g. a patient in an initially safe environment which later becomes unsafe & requires a new plan (for example, abusive or violent patients, relatives or bystanders, or environmental dangers)
- In these cases, OODA could be used to document & assist with decision making during parts of jobs.
- CHEATED, CHARTIE, OODA and Douglas et al’s (2013: 39) version which includes ROS all have some sort of evaluation featured as part of their models. A useful addition?
Comments? Questions? Add them below –>

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References

Beebe, R. & Myers, J. 2010. Foundations of Paramedic Care, Volume 1. Delmar: Cengage Learning

Blaber, A.Y. & Harris, G. 2011. Assessment skills for paramedics, Berkshire: Open University Press

Douglas, G. et al, 2013. Macleod’s Clinical Examination, Edinburgh: Elsevier. Ed. 13.

Farrington, G. 2018. ABCDE Approach, Available Online: https://geekymedics.com/abcde-approach/ (Accessed 16/06/18)

Geeky Medics, 2018. Documentation. Available Online: https://geekymedics.com/category/communication-skills/documentation/ (Accessed 16/06/18)

Gregory, P. & Mursell, I. 2010. Manual of Clinical Paramedic Procedures, Oxford: Blackwell Publishing

Jenkins, S. 2013. History taking, assessment and documentation for paramedics. Journal of Paramedic Practice, 5 (6): 310-316

Larimore, W.L. & Jordan, E.V. 1995. SOAP to SNOCAMP: Improving the medical record format, The journal of family practice, 41 (4): 393-398

Lenert, L.A. 2016. Toward Medical Documentation That Enhances Situational Awareness Learning, AMIA Annual Symposium Proceedings Archive, 2016: 763-771

Marinis, D. et al (2010) ‘If it is not recorded, it has not been done!’? consistency between nursing records and observed nursing care in an Italian hospital. 19. (11-12). 1544-52. doi: 10.1111/j.1365-2702.2009.03012.x

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

Potter, L. 2018. How to document a patient assessment (SOAP), Available Online: https://geekymedics.com/document-patient-assessment-soap/ (Accessed 16/06/18)

Resuscitation Council, 2018. The ABCDE Approach, Available Online: https://www.resus.org.uk/resuscitation-guidelines/abcde-approach/ (Accessed 16/06/18)

Snadden, D. et al. 2013. History Taking. In Douglas, G. et al Macleod’s Clinical Examination, Edinburgh: Elsevier. Ed.13.

The Regents of the University of California, 2015. Adult Review of Systems. Available Online: https://meded.ucsd.edu/clinicalmed/ros.htm (Accessed 09/06/2018)

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This post is yet to be peer reviewed. Human error may still exist in the reference list or in the body of the article. Please get in touch if you have any comments.
June 17, 2018
Free Ventilator Downloads from Smiths Medical

So far, Article 999 has a reasonable collection of information and videos about positive pressure breathing and ventilators used in prehospital emergency care. Smiths Medical is behind the PneuPac ParaPac. They have kindly given their permission to share the following documents, which are available for those who want to read more, find out about other available ventilators, or find an answer not available here.

ParaPAC Plus

BabyPAC self-assessment checklist

BabyPAC Transport Ventilator

Automatic Resuscitator

Medical Care under extreme Conditions

Difficult Environments

An introduction to Oxygen Therapy

Emergency and Transport Ventilation an introductory guide

Add feedback below ↓

January 17, 2018

Ventilators: Why, What, How, When?

Made by UK Paramedics, this video demonstrates how to use the PneuPac ParaPac ventilator.

What is the relief pressure dial on the ventilator?

What is positive pressure breathing?

What is Negative Pressure Breathing?

The Discovery of Negative and Positive Pressure Ventilation – Fast Fact

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.

Why use the ventilator?

Research suggests that mechanical ventilators can reduce the variability of breath timings & as a result, capnography readings. They can also increase the likelihood of ‘effective ventilation’ (Owen and Castle, 2006)

To quote from Gregory & Mursell (2010: 47) ‘A high flow rate over a short inflation time inevitably produces a high peak airway pressure in an unprotected airway [as with BVM technique]. High peak airway pressure overcomes the pressure of the lower oesophageal sphincter and causes gastric inflation. […] Use of […] mechanical ventilation may help to overcome the high pressures involved. […] In an intubated patient or a patient with an LMA in situ, use of a mechanical ventilator has been shown to allow paramedics to accomplish extra tasks, document better, and provide better patient care’ (Gregory & Mursell, 2010: 47)

What?

This is a time-cycled, volume preset flow generator (Baker, 2012). In other words, the pressure can vary, volume is always the same, and the air must be delivered within a preset time, which helps to control the tidal volume.

There are many different types. One of the most common ones in UK ambulances at this time (Gregory & Mursell, 2010: 44) is the Pneupac paraPAC (Smiths Medical, 2017) but the ParaPac Plus may soon replace it.

Here are the useful parts:

The supply gas failure alarm
The inlet connection
The relief pressure control
The ‘main pneumatic switch’
Air mix control
Inflation pressure monitor
Frequency control
Tidal volume control
(Pilbery and Lethbridge, 2016: 189)

How?

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.
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.
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.
Next, check the indicator shows white for O2.
Connect the patient circuit [shown in video].
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).

When?

– AACE (2016) recommend considering ventilation if a ptn’s o2 sats <90 on high con o2,
if the RR is <10 or >30 bpm or if there is ‘inadequate chest expansion’ (p42) but the mechanical ventilator is to be used …
– for ’emergency and transport ventilation’ in 5kg + patients (Smiths Medical, 2017)

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)

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December 29, 2017

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.

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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.

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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.

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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.

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November 16, 2017
What is positive pressure breathing?

Positive pressure refers to the way artificial ventilation ‘inflate[s] the lungs’ (Hess & Kacmarek, 2014). ‘Normal breathing depends on drawing in air to the lungs by creating a partial vacuum inside the chest cavity’ (Baker, 2016: vi). The mean airway pressure, an average combined of ‘the amount and duration of pressure applied during’ expiratory and inspiratory phases in normal breathing is negative (Hess & Kacmarek, 2014: 420 ebook). See the article on negative pressure breathing for more information. Intermittent positive pressure ventilation, on the other hand, is for inspiration the ‘exact reverse of this process with air being forced into the lungs’ (Baker, 2016: vi).

Positive pressure ventilation includes the use of bag-valve-masks, but the majority of this article will focus on the ventilator.

Upcoming articles will discuss the specific settings and how-tos relating to the Pneupac ParaPac ventilator. Current links:

What is Negative Pressure Breathing?

The Discovery of Negative and Positive Pressure Ventilation

What is the relief pressure dial on the ventilator?

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Inspiration: Expiration

Ventilators have 4 phases of operation:
1. ‘The inspiratory phase’
2. ‘Cycling between the inspiratory (I) and expiratory (E) phase’
3. ‘The expiratory phase’
4. ‘Cycling between the E and I phase’
(Baker, 2016: 117)

The majority of ventilators are set to an I (Inspiratory) to E (Expiratory) ratio of 1:2, i.e. the expiratory phase is twice as long as the inspiratory phase, ‘which mirrors normal breathing’ (Baker, 2016: 108). If required, some ventilators allow this setting to ‘be altered to assist with restrictive lung diseases’ (Baker, 2016: 108). ICU ventilators contain additional settings that alter this ratio, including a ‘respiratory pause’ between the I and E phases ‘to allow distribution of gas within the lungs’ (Baker, 2016: 108).

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Mechanics

So, inspiration occurs when air is ‘forced into the lungs’ (Baker, 2016: vi). Expiration, however, occurs when ‘the ventilator stops delivering a positive pressure and the patient breaths out passively, as in normal breathing. This passive expiration (E) is ensured by the elastic recoil of the lungs and the chest wall’ (Baker, 2016: 108). The timing is aided by a ‘pneumatic oscillator’ (Baker, 2016: 22).

The gas is delivered by the ‘patient circuit’, which also ‘evacuate[s] expired CO2’ (Baker, 2016: 109). This is delivered ‘as close as possible to the airway device being used’ by a valve (Baker, 2016: 109). There are also filters to prevent contamination of the ventilator from the patient.

Early ventilators had a ‘lack of interactivity with the patient’s own breathing efforts if there was only partial respiratory failure’ (Baker, 2016: 22) but modern ventilators tend to have different modes to account for this and additional settings beyond a simple tidal volume dial. In particular, ventilators feature a ‘demand valve’ which detects when a patient takes a breath (Baker, 2016: 22). There are also settings for tidal volume and ventilation frequency. These settings will be discussed in upcoming articles.

The Pneupac ParaPac (Smiths Medical)

Read more: What is the relief pressure dial on the ventilator?

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The Positives and Negatives

The main positive effect of artificial ventilation is fairly obvious: it assists with the ventilation of a patient who is completely or partially unable to breathe normally. There are however a number of negative effects created by positive pressure ventilation. Related to these is the fact that mechanical ventilation can cause ‘heterogeneity’ of the lungs, meaning that ‘some lung units are prone to overdistension and others are prone to collapse’ (Hess & Kacmarek, 2014: 493). These are part of the reason most ventilators have relief pressure settings. This setting will be discussed in an upcoming article. You can check back here for the link.

Positive pressure ventilation can cause or effect the following:

The following are unavoidable results of ventilator use:

Decreased cardiac output
…Leading to ‘hypotension and potential tissue hypoxia. This effect is greatest with high mean airway pressure, high lung compliance, and low circulating blood volume’ (Hess & Kacmarek, 2014: 513). The high pressure ‘decreases venous return and right heart filling, which may reduce cardiac output’ (Hess & Kacmarek, 2014: 513).

I.e:
High pressure –> decreased venous return
Low pressure –> increased venous return

This pressure is normally lowest ‘during inhalation’, so venous return would be highest. But with positive pressure ventilation, ‘venous return is greatest during exhalation’ as opposed to inhalation (Hess & Kacmarek, 2014: 513-520).

Renal and gastric effects
Mechanical ventilation reduces urine output due to ‘decreased renal perfusion’ which results from ‘decreased cardiac output’ (Hess & Kacmarek, 2014: 527). Unfortunately this can cause many of the issues common with fluid retention. Similarly, gastric distension can result, along with gastrointestinal bleeding’ (Hess & Kacmarek, 2014: 533).

Increased intracranial pressure
…in head injury patients, due to ‘a decrease in venous return, which increases intracranial blood volume and pressure’ (Hess & Kacmarek, 2014: 540).

Pneumonia may occur, especially due to invasive ventilation which is the form in emergency practice (non-invasive refers to ventilatory support such as CPAP). It ‘results from aspiration of oropharnygeal secretions around the cuff of the endotracheal tube’ (Hess & Kacmarek, 2014: 499).

The following can occur as a result of ventilator settings:

Hyperventilation and hypoventilation
These risk effecting the pH, and causing respiratory alkalosis (Hess & Kacmarek, 2014: 499)

Oxygen Toxicity due to high oxygen levels (Hess, 2014: 506)

A Shunt is usually partly decreased but settings can change this:
A shunt is ‘perfusion (blood flow) without ventilation’, which happens ‘when blood flows from the right heart to the left heart without participating in gas exchange’ (Hess & Kacmarek, 2014: 427). There are two different types of shunts: capillary and anatomic. The first occurs when the alveoli are not ventilated. One example of this is pneumonia (Hess & Kacmarek, 2014: 427). The latter type of shunt occurs when blood flow ‘completely bypasses the lungs’, which can sometimes happen with ‘congenital cardiac defects’ (Hess & Kacmarek, 2014: 427).

Positive Pressure Ventilation’s typical effect is to decrease capillary shunt by improving ‘the distribution of ventilation, particularly by improving the ventilation of previously underventilated areas of the lungs’ (Hess & Kacmarek, 2014: 427-446)

Despite the above improvements, if the settings are not ideal hypoxemia can result. This is the same outcome as a shunt but would in this case be caused by ‘redistribution of pulmonary blood flow to unventilated regions’ due to ‘overdistension of some lung units’ (Hess & Kacmarek, 2014: 324). Positive pressure ventilation can also increase anatomic shunt (Hess & Kacmarek, 2014: 441)

Also due to incorrect settings, the following can occur as a lack of pressure or volume:

Atelectasis occurs when the pressure or volume during or after artificial ventilation isn’t enough to inflate the lungs –> complete or partial collapse.

Atelectasis ‘is larger with obese patients and when a higher fraction of inspired oxygen (FI02) is used […]. During mechanical ventilation […] atelectasis may occur when lungs are underinflated due to low tidal volumes, or when compression occurs (such as patient position or obesity)’ (Open Anesthesia, 2017). If the volume or pressure isn’t enough to ‘prevent the alveoli from collapsing’ (Open Anesthesia, 2017) then regardless of ventilator type (pressure vs volume controlled) atelectasis may result.

The following can occur as a result of apparatus setup:

Dead Space can be increased by mechanical ventilation (Hess & Kacmarek, 2014: 471). It may be ‘reduced by an artificial airway (ETT) but is increased by increasing distance from the end of the ETT to the means of evacuating CO2 in mechanical ventilation’ (Baker, 2016: 111). Size, age, upright postures and neck extension also increase it (Baker, 2016: 111).

The following can occur due to overdistension:

Barotrauma = ‘alveolar rupture due to overdistension’, which can cause numerous problems including pneumothorax (Hess, 2014: 480). Volume generators have a ‘safety valve which activates at a preset pressure’ to avoid barotrauma’ (Baker, 2016: 118). This will be discussed in an upcoming article.

Ventilator-Induced lung injury caused by overdistension. Massively effected by ventilator settings for tidal volume and relief pressure (Hess, 2014: 493)

There are additional risks of positive pressure ventilation, particularly mechanical ventilation. Some of these are related to the use of airway adjuncts. Others are related to the removal of the ventilator. To read more, check out the references below.

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Types of Positive Pressure Ventilation

‘A spectrum of modes exist between total artificial ventilation and a patient who is still breathing spontaneously but with reduced efforts’ (Baker, 2016: 105).

There are two main types of ventilators:
– Pressure generated
– Volume generated

Pressure generators ‘provide a constant pressure during the inspiratory phase’ (Baker, 2016: 118). Volume generators release gas once a set volume has been reached. In each one, only the pressure or the volume is a constant. Everything else is relative and will adjust until the preset parameter of volume or pressure has been reached (Baker, 2016; Hess, 2014).

Issues
‘The problem of pressure generation is that it cannot guarantee an adequate Vt [volume] in situations where the lung mechanics are abnormal or where a guaranteed Vt is required due to life-threatening hypoxia. They are therefore not suitable for most emergency ventilation, with the notable exception of neonatal and infant ventilation where flow generators are contraindicated due to the fragility of the lung tissue’ (Baker, 2016: 118).

Additional Types
Most ventilators switch from inspiration to expiration by ‘time cycling’ (Baker, 2016: 119). However, this can also be due to volume or pressure cycling. The time cycling ratio is usually 1:2 for I:E, in other words the expiration time is twice as long as the inhalation time. ‘Ventilation modes can best be understood as a spectrum describing the work of breathing done by the ventilator and by the patient’ (Baker, 2016: 122.

The modes are: Controlled Mandatory Ventilation, in which ‘ventilation is provided entirely by the ventilator’ (Baker, 2016: 122), Assisted Controlled Ventilation which is fairly self-explanatory, and Synchronised Mandatory Ventilation, in which ‘the patient’s respiratory efforts in initiating a ventilation are synchronised with ventilations provided automatically by the ventilator.’ This is best used to supplement the patient’s efforts. It’s otherwise known as ‘assist-control’ and is typically found in ICU. (Baker, 2016: 123).

In portable ventilators the modes are:
Intermittent Mandatory Ventilation, Synchronised intermittent mandatory ventilation, and synchronised mandatory minute volume but only the latter two are still in use. The second overcomes the problems of the first, ensuring that breaths are supplemented by the ventilator and that supplemented breaths are activated only when there is a certain trigger e.g. low pressure. There is a modern, more complex version of this now in use in hospitals but this may exist in emergency ventilation practice to assist a patient who is ‘in partial respiratory failure’ (Baker, 2016: 124).

The first two divide minute volume between the ventilator and the second. The latter is based on time, which is compared with a ‘set minute volume. If there is a discrepancy between the actual minute volume and the set delivered minute volume, an automatic ventilation is delivered which corrects the difference’ (Baker, 2016: 124).

Because there is an issue of the ventilator being unable to tell the difference between dead space ventilation and alveolar ventilation, Pneupac have modified the above with a series of Ifs (if the patient takes a breath, if there is no further breath, if the tidal volume is too low, etc) that adjusts settings accordingly (Baker, 2016: 124). There are more modes that exist for ICU ventilators, which tend to be a lot more complex in design (Baker, 2016).

Read about the solution: What is the relief pressure dial on the ventilator?

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CPAP

CPAP is also a form of positive pressure breathing and is designed ‘to improve oxygenation in lungs that may not be exchanging oxygen with the blood adequately’ (Baker, 2016: 126). There is a constant pressure in CPAP, versus ‘different pressures during inspiration and expiration’ in BIPAP’ but both are designed to allow the patient to do all the work of breathing. They merely increase oxygen and make inspiration easier while increasing the work of expiration. ‘Breathing with CPAP has been compared to the sensation of breathing against a very strong wind’ (Baker, 2016: 128). They ‘open up (recruit) alveoli in the lungs that may be non-ventilated.’ (Baker, 2016: 127). Both push back fluid ‘into the circulation via lymphatic drainage of the lung interstitial space’ and increase ‘the diffusion of oxygen into the pulmonary capillaries’ (Baker, 2016: 127).

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PEEP

Positive End Expiratory Ventilation applies ‘a positive pressure to the patient during the expiratory phase’ to ‘increase the functional residual capacity of the lungs and thus the efficiency of oxygenation of the blood’ (Baker, 2016: 126). ‘In order to be able to deliver a set tidal volume against variable lung compliance and airway resistance, resuscitation ventilators should be time-cycled, volume preset flow generators’ (Baker, 2016: 132).

References

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

Hess, D. & Kacmarek, R.M. 2014. Essential of Mechanical Ventilation (ebook), McGraw-Hill Education: New York

Open Anesthesia, 2017. Ventilator Settings: atelecasis, Available Online: https://www.openanesthesia.org/ventilator_settings_atelectasis/ (Accessed 09/11/17)

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

November 10, 2017