Non Invasive Ventilation

Authors: Michelle Tipping / Reviewer: Charlotte Davies / Codes: CAP6, HAP6, RespiP2, SLO6 / Published: 10/09/2021

This blog was going to be a #rcemblogs blog, but then we included it as part of our COVID blog. Now COVID isn’t an educational priority, we’ve moved the NIV blog to its own blog page to make it easier to find.

NIV is considered an aerosol generating procedure – there’s a summary of some of the infection control precautions from the BTS here.

Non-invasive ventilation (NIV) can seem daunting to those who are not used to it. It is a therapeutic intervention overwhelmed with confusing abbreviations and lots of seemingly complex underlying physiology. However, in reality it is a really useful & simple tool that clinicians can instigate to make a major impact on stabilising a sick patient with respiratory failure. This guide is not intended for those who are experienced ITU types, however, if you are one of the millions of front-line staff looking to help during our latest respiratory pandemic with little experience in the use of NIV please read on. Please note; this guide does not include use of NIV in our paediatric population.

The Basics – When to

Before we get started, it is important to know when NIV may help. In simple terms NIV is a method of delivering oxygen to the lungs using pressure to reduce the amount of work the patient has to do to breathe. Therapeutically it sits between a simple facemask (the old non-rebreather by every hospital bed) and full intubation. It is delivered by a tightly fitting face mask which can induce claustrophobia and panic in the calmest of individuals so remember, even if you feel the same about setting it up, the patient needs you to seem calm, so, take a deep breath and read on. There’s some tips on how to avoid panic in your patient on #rcemblogs – explain what you are doing, take it slowly, and give the patient control. NIV can be used in a wide range of settings. If you are reading this today it is likely that you are considering its use with Covid-19. However, we will be seeing many patients with normal underlying lung diseases (COPD, bronchiectasis, pneumonia) during this time who may benefit from NIV just as they would in normal circumstances (despite having a super-added viral infection). Essentially NIV is really useful when patients are struggling to absorb enough oxygen (Type I respiratory failure) OR when you can’t get enough oxygen in and carbon dioxide out (Type II respiratory failure). Although research is still limited, initial reports from the Covid front-line suggest that the pliability of the lungs is preserved so NIV may be very useful in the combined situation. Relevant examples of Type I include pneumonia and acute respiratory distress syndrome (ARDS) and Type II include COPD. These pathologies will form the biggest extent of our work load during the Covid-19 epidemic and we should expect to see many patients with a mixed respiratory picture.

The indications for NIV are well documented but essentially include: pH <7.35 pCO2 >6.5 RR >23 Failure of medical therapy, Incl: steroids, nebulisers, controlled O2

These figures should be taken from an arterial blood gas (ideally with local anaesthetic!) not a point of care venous blood gas! There are a few absolute contraindications to the use of NIV that we should all be aware of: Facial Burns Fixed upper airway obstruction Facial deformity (mask won’t fit) Pneumothorax Respiratory Arrest The relative contraindications will be discussed in the last section: “should you?”.

How to

Before you get started fitting a patient for NIV it is important to understand some basic physiology and what you are trying to achieve. (Yes, I’m going to try & explain some of those annoying abbreviations!) Firstly, there are 2 types of NIV: CPAP (continuous positive airways pressure) and BiPAP (bilevel positive airways pressure). Essentially most patients who utilise NIV at home for conditions like sleep apnoea will have a CPAP machine as they are more portable. Hospital settings tend to utilise BiPAP. BiPAP is generally better tolerated and is the ‘go-to’ for most emergency departments when starting NIV. BiPAP delivers a couple of things that can make it more useful than CPAP… 1. You can set a breathing rate – although not enough to take over breathing altogether, it can encourage a better rate. 2. You set the machine to deliver 2 pressures; one for inspiration (known as IPAP – inspiratory positive airways pressure) and one for expiration (EPAP – expiratory positive airways pressure). By having a lower positive pressure during expiration patients find it more comfortable than CPAP where they have to exhale against a high pressure system.

By constantly delivering some form of pressure (CPAP or BiPAP) then when a patient exhales the alveoli don’t completely collapse. This is obviously more energy efficient than try to open up closed airways and means oxygen delivery starts earlier because the airway is already open during inhalation…creating a win-win situation! There are lots of different machines on the market, but they are all essentially the same. Standard starting pressures for BiPAP are: IPAP – 8-10 mmHg EPAP- 2-4 mmHg Once the patient is undergoing therapy the settings can be altered to optimise ventilation.

 

It is recommended that the patient has a repeat blood gas after an hour to check response to therapy aiming for sats of 88-92%in COPD and 94% in the otherwise well with resolution of hypercarbia. It should also be repeated an hour after any change in settings and after 3 & 12 hours of treatment. There’s a little bit of an art too it, but generally, if PO2 still low – turn up O2 and / or turn up EPAP 2-3 cmH2O a time to max of 12cmh2o consider increasing IPAP to a max if 20cmh20 if estimated volumes are less than estimated for patients size (then expert discussion).  If PO2 high – turn down O2, and then turn down EPAP. If CO2 high – consider increasing ventilatory rate and then turn up the IPAP to increase the ventilatory volume delivered. Increase the IPAP in steps of 2-3 cmh2o to avoid sensation of sudden change in pressure and improve tolerance to increases and be prepared to increase pressures to max of 20 in steps every 5mins. The rough aim is a volume of 5-7ml/kg of ideal body weight. So for your average 70kg person (!!), 350 –  490ml volume.

It is also possible to run nebulised drugs through the NIV circuit and you can give positive suggestions, as well as a light sedative (0.25mg lorazepam) to aid tolerance if your patient is agitated. Good resources to help with the simple mechanics of setting up NIV & how it works can be found here: EM3FOAMed #EM3 CLAHRC NWL ICU Advantage OME Twitter video . The second video above raises some other important points regarding good explanation to patients of what you are trying to achieve and the limits of NIV – before starting NIV it is important to have ceilings of treatment in place. i.e. should it fail or the patient start to deteriorate what would you do next? Is the patient a suitable candidate for invasive mechanical ventilation?

Should you?

NIV has most definitely proven its worth over the past 20 years in everyday respiratory challenges such as COPD. It is recommended by the British Thoracic Society in most situations. Its use in isolated ARDS remains controversial but it will likely be of benefit to those with underlying abnormal respiratory physiology. Physicians should be aware that it is not a ‘quick fix’ therapy and we would expect patients on NIV to need ongoing support for several days including a weaning period. Reports from Italy are also indicating the period of respiratory support required is longer than normal in Covid-19 which puts a bigger drain on resources.

There are some standard relative contraindications to be aware of:
pH <7.15 pH <7.25 with additional adverse features
GCS < 8 Confusion/agitation Cognitive impairment.

If any of these features are present, then the use of NIV should be discussed with a senior doctor proficient in its use (ITU/HDU consultants / respiratory consultants / ED consultants), as intubation may be preferable. One of the problems with NIV is leaking of the masks and aerosolization of any pathogen increasing the risk of infection to those administering care or in the near vicinity (known as an aerosol generating procedure – AGP). This has been raised as a concern in lots of the current literature regarding treatment of potential and confirmed Covid-19 patients.

Summary

Full page version here.

The bottom line: If you do not have the resources to isolate your patient and protect yourself and others then this is not a modality you should be using to treat Covid-19 patients, although we accept CPAP may be a useful bridging tool before intubation.  If you’re going to use it, deliberately practice -as practice makes perfect. CPAP and NIV hacks here.

You can now complete our SBA on this topic. Please log in to access it.

 

References & Useful Resources
1. Simon Carley (2020) St.Emlyn’s Covid 19 Podcast from Italy with Roberto Cosentini
2. British Thoracic Guidelines (2016) BTS/ICS Guideline for the Ventilatory management of Acute Hypercapnic Failure in Adults
3. Josh Farkas (March 2020) COVID-19 EMCrit
4. Public Health England (March V1 2020) Covid-19 Guidance for infection prevention and control in healthcare settings

11 Comments

  1. Dr Gasser Ahmed says:

    Basic and useful, Thanks

  2. Hasanen Abdulhameed says:

    very useful

  3. Dr Chandika Amarasiri Gunawardena says:

    good revision

  4. Dr Ying Chung Tony Lee says:

    thank you. very useful

  5. Dr. RaviRaja Muddana says:

    I appreciate the way this topic is presented in a Non-Confusing manner

  6. Dr Preetesh Sahani says:

    Simple and lucid

  7. Anas Mohamed says:

    thanks for that

  8. Dr Peter Cuthbert says:

    useful thanks

  9. Shawgi MOHAMED says:

    Brief and useful

  10. MIrjana Starinac-Baldwin says:

    Very informative, thank you

  11. Dr Julius Samuel Kumar Manoharan says:

    was precise and very informative. thank you.

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