Author: Dr Matthew Durie
Peer reviewers: Dr Vinodh Nanjayya, Dr Lloyd Roberts, and Prof Andrew Udy
Guidance for the role and use of non-invasive respiratory support in adult patients with coronavirus (confirmed or suspected), March 26, 2020. [Accessed April 1 2020]. Available at URL: https://www.england.nhs.uk/coronavirus/wp-content/uploads/sites/52/2020/03/CLEARED_Specialty-guide_-NIV-respiratory-support-and-coronavirus-v2-26-March-003.pdf
In contrast to ANZICS Guidelines which recommend against the use of non-invasive ventilation (NIV), the National Health Service (England) have released guidance discussing the role and methods to provide NIV to patients with coronavirus disease 2019 (COVID-19). Also, in contrast to the ANZICS guidelines, the NHS guidance recommends against the use of high flow nasal oxygen (HFNO). the use of high flow nasal oxygen (HFNO).
A summary of the NHS recommendations is as follows:
- Treatment escalation plans and limitations to treatment, if any, should be established early in all patients
- HFNO is not recommended in COVID-19 management
- NIV may be
indicated in the following circumstances:
- As a ceiling of treatment
- Trial to avoid intubation
- To facilitate extubation
Settings & targets:
- CPAP for hypoxaemic respiratory failure, commencing at 10 cmH2O pressure and an FiO2 of 0.6, with potential to increase to 12-15 cmH2O and FiO2 1.0.
- BiPAP may be used for hypercapnic acute on chronic respiratory failure
- Target SpO2 94-96%, or 88-92% for patients with acute on chronic respiratory failure
Principles of use:
- Ensure steps taken to minimise nosocomial spread (below)
- Consider methods to minimise agitation & distress
- Establish clear escalation plans/criteria for intubation
- Avoid over-ventilation and ‘patient-induced lung injury’ (PILI)
- During breaks off NIV use high flow face mask oxygen (not HFNO) or non-rebreather mask.
Recommendations to minimise nosocomial spread:
- Negative pressure room (>10 cycles/ hour air exchanges)
- Neutral pressure room or a simple side room (if negative pressure room not available)
- Cohorting if outside ICU, with clear plan for intubation if appropriate
- CPAP interface, in order of preference:
- Full face mask, non-vented, with viral filter on expiratory limb
- Helmet CPAP (with air cushion, if available) if full face mask not possible
- Standard mask (least preferred option)
- Must have ability to entrain oxygen
- Avoid vented masks
- Use HME/viral filter fitted to all exhaust systems
- Ensure staff PPE and methods to inadvertent avoid circuit disconnection
The role of NIV and HFNO in COVID-19 remains unclear, with little direct evidence from COVID-19 patients of either efficacy or risk. This uncertainty, plus the purported risks of aerosolization generation and delayed intubation have led to varying recommendations between authorities (World Health Organisation (WHO), ANZICS, NHS and Surviving Sepsis Campaign (SSC) now all provide different advice, Table 1).
Table 1: Summary of recommendations from different groups
WHO = World Health Organisation (March 13, 2020); ANIZCS = Australian and New Zealand Intensive Care Society (March 16, 2020); SCCM = Surviving Sepsis Campaign (March 23, 2020); NHS = National Health Service (March 26, 2020).
In general, there is concern about the efficacy and safety of NIV in the management of acute respiratory distress (ARDS). In ARDS cohorts, NIV prior to intubation was associated with high failure, delayed intubation and an increased risk of mortality (LUNG-SAFE observational study and FLORALI RCT). Additionally, there is a suggestion that HFNO may be superior to NIV in these circumstances, particularly in patients with a PaO2:FiO2 ratio of ≤ 200mmHg (FLORALI). In contrast, NIV may be beneficial post-extubation in reducing re-intubation rates in high risk patients, though without improving mortality or ICU length of stay (HIGH-WEAN RCT). There may also be circumstances in which NIV is clearly beneficial, for example, patients with chronic obstructive pulmonary disease (COPD) or cardiogenic pulmonary oedema. The role of NIV in these patients, who may have concurrent confirmed or suspected SARS-CoV-2 is perhaps clearer than for patients with hypoxic respiratory failure due to COVID-19 lung injury.
The main criticism of the NHS guideline is that it doesn’t provide a review of the evidence/rationale behind the recommendations. The NHS authors propose that lung compliance of COVID-19 patients is generally preserved hence the rationale for CPAP, however this may not always be the case. Positive pressure ventilated, spontaneous breathing patients may develop what the authors refer to as ‘patient-induced lung injury’, due to generation of excess tidal volume or elevated transpulmonary pressure, the potential mechanism of which is described by Brochard et al. 2016. The NHS authors warn clinicians to be vigilant against harmfully high tidal volumes, but do not provide specific criteria against which to titrate CPAP pressure (in contrast to the FLORALI RCT protocol, for example).
Both NIV with vented and non-vented masks have the potential to generate dispersal jets containing droplet or aerosolised viral particles with a risk of infection to health care workers (HCW) and other patients. During SARS in 2002/2003, non-invasive ventilation was associated with increased risk of HCW infection. Under simulated conditions; vented masks may generate large dispersal plumes up to 65cm in length. With well fitting, non-vented NIV masks, leakage plumes appear to remain limited to around patient’s head and face, although evidence is poor, and will depend on fit. Importantly, HCW intervention is still required to apply and remove the mask, with potential for droplet or aerosolization while in close proximity. A poor fitting mask may both increase leakage and the frequency of HCW interventions. Distress or agitation may lead to a poor fitting mask, frequent removal, or disconnection of the circuit. Patients on NIV may therefore require closer supervision, increasing risk of HCW exposure. Finally, NIV may delay early intervention for patients who are deteriorating, resulting in intubation under more urgent conditions, where a risk of PPE breach may be higher.
While endorsing CPAP, the NHS authors recommend against the use of HFNO, citing a ‘lack of efficacy, oxygen use and infection spread.’ Like NIV, HFNO may generate dispersal plumes of exhaled air however droplet deposition from HFNO under simulated conditions appears to be limited to within 30 cm of the face. Furthermore, co-operative patients may be able to adjust HFNO cannulae themselves without HCW being in close proximity, and wear a mask to reduce forward droplet spread. Like NIV, the potential for aerosolization remains unclear.
Whether and when patients with COVID-19 should be offered NIV or HFNO remains contentious. For patients who have limitations to treatment, for patients with acute on chronic respiratory failure, for facilitating extubation (for example, obese patients) NIV may offer a viable alternative. In these circumstances, the NHS guidelines provide clear advice on how to use NIV and minimise the risk of nosocomial spread. The main criticism of this guideline is that it doesn’t provide a review of the evidence/rationale behind the recommendations.
Further in vivo evidence regarding the safety and potential role for NIV or HFNO is desperately needed, as health systems face having to rationalise treatment to patients due to a lack of resources. For clinicians who choose to offer NIV to patients with COVID-19, the NHS guidance otherwise offers clear and detailed advice on how to provide this in a way that reduces (as much as possible) risk to patients and staff, however additional guidance on how to titrate therapy to avoid ‘patient-induced lung injury’ may be necessary to avoid adverse outcomes from the therapy.
Note: This review does not imply an endorsement of any particular guideline, and the opinions offered are the author’s own, with best available evidence at the time of writing. Clinicians should adhere to local guidelines where possible.
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