COVID-19 – Use of non-invasive oxygenation CPAP devices in prehospital and intra-hospital emergency care
Non-invasive ventilation supports use in COVID-19 patients
Patients with COVID-19 appear to have a particular clinical presentation compared to other patients with acute respiratory distress syndrome (ARDS). This is not based on scientific evidence that is yet to be substantiated, but it appears to be a particular aspect that emerges from various resuscitation returns that manage these patients. For example, in invasive mechanical ventilation, these particular characteristics are as follows:
- Low pressures are observed in ventilated patients: it seems that lung compliance is close to normal unlike most traditional ARDS patients.
- Emerging concept of “silent hypoxemia”: near-normal lung compliance may result in relatively low pre-intubation work of breathing in the patient compared to the depth of hypoxemia.
- Highly recruitable lungs: Patients often have a good response to recruitment using high levels of PEEP.
- Favourable pronation response: with typical basilar peripheral consolidation on CT scan results, this may be consistent with a significant contribution from basilar atelectasis.
The pathophysiological hypotheses underlying the rapid progression of some patients from moderate hypoxemia to severe ARDS appear to be consistent with a rapidly progressive alveolar collapse phenomenon. The alveoli begin to collapse, distorting the lung architecture and promoting the collapse of neighbouring alveoli. When this cascade is no longer compensated for, this can lead to rapid deterioration requiring intubation. Once patients are intubated, high levels of positive airway pressure recruit these collapsed alveoli and this may explain why these patients can go from very high FiO2 requirements to significantly reduced requirements over a period of a few hours.
In this context, what is the place of a non-invasive mode of respiratory assistance? The pathophysiological model described above suggests that COVID-19 patients essentially need positive pressure more than anything else. This is because their respiratory work often seems tolerable and therefore, they do not require much inspiratory assistance (IA) to relieve it. In addition, the application of mechanical assistance generating a CEW results in a large tidal volume (VT) that is detrimental to this pathophysiological profile.
The ARDS of a COVID-19 therefore does not behave like a typical ARDS, implying that the initial therapeutic approach to intra- and prehospital emergencies may be slightly different. Indeed, the best way to provide significant positive pressure without generating a high tidal volume is to simply apply continuous positive pressure (CPP). Indeed, this modality can provide significant positive pressure to allow for greater alveolar recruitment. CPP, which is commonly used in out-of-hospital EMS and intra-hospital emergency departments, may have several advantages for the management of COVID-19 infection in the emergency department:
- It allows the maximum mean pressure to be reached without intubation.
- It does not increase the VT, which may promote “protective” lung ventilation.
- With appropriate filters, its use can be reasonably safe with respect to viral transmission.
What is the role of CPAP in COVID-19?
There is no evidence-based answer to date. There are many strong opinions, and initially, guidelines against its use, but almost no data, especially specific to COVID-19 infection. The majority of available data on NIV consists largely of data related to the use of non-invasive mechanical ventilation with bi-level levels (sometimes inappropriately referred to as BiPAP) rather than continuous positive airway pressure (CPAP) whether it is generated by a mechanical ventilator (Mechanical-CPP or mCPP) or by an open-circuit expiratory valve created by the venturi effect or by a flow generating virtual valve (Boussignac’s CPAP). Indeed, these two modalities are invariably grouped together under the generic term NIV although they are very different.
CPAP is certainly not the treatment of choice for all COVID-19 patients. A “helmet” type interface, such as is widely used in Italy, may be optimal if it is available to avoid mask seal problems. However, very few teams use them in other European country, but a seal-applied NIV mask appears to be as effective in limiting droplet aerosolization. Thus, CPAP could potentially play an interesting role in certain situations :
- Patient with worsening hypoxemia (e.g. requiring more than 5-6 L/min O2), who is not in distress and has no other organ failures.
- Patients whose preference is not to be intubated (advance directives).
- Absence of available mechanical ventilators: the price of a set of Boussignac CPAP is derisory compared to conventional resuscitation methods (a few dozen euros), and the available stocks are large.
- Moreover, if CPAP could avoid intubation even in only 20 to 40% of patients, this could help to avoid depletion of the stock of necessary ventilators.
- Absence of a team present to intubate the patient: e.g. a small hospital without the medical resources needed for immediate intubation (e.g. EMS and/or outpatient emergency physician).
As with all forms of NIV, careful monitoring is the key to security. This is particularly important for patients with COVID-19, who can develop this “silent hypoxemia” that makes them look much better than they actually are.
How do you use CPAP in the ER and in EMS?
The pressure can be increased to a fairly high level with good tolerance (up to 15 cmH2O) without the risk of gastric insufflation or aspiration . FiO2 can be titrated according to the patient’s oxygen saturation (SpO2). Thus, a favourable response to CPAP may reflect pulmonary recruitment and decreased O2 requirements and, conversely, increased O2 requirements may be a good indicator of the need for intubation.
The procedure is simple and proceeds as follow (Fig. 1):
- The Boussignac-CPAP is indicated in COVID-19+ (or possible) patients in need of oxygen (Sp02 < 92% in ambient air).
- It is used continuously or discontinuously depending on the needs.
- System set-up: assembled 3 elements (face-mask with its attachment system, adapted filter HME type, then the Boussignac-CPAP).
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There is nothing specific in the monitoring of Boussignac-CPAP use during COVID-19 patients’ care: mental state, tolerance, oxygenation level (O2 flow, SpO2), respiratory work (breathing frequency, signs of hypercapnia, etc), blood gas if clinically justified. The use of Boussignac-CPAP is associated with close or continuous monitoring (depending on clinical status) of Sp02.
When using the Boussignac-CPAP the wall mounted O2 flowmeter is adjusted with a flow rate of 02 increasing from 6 to 15 L/min to obtain a Sp02> 92%. This flow generates a positive expiratory pressure (PEP) between 0.5 cmH20 and 3.5 cmH20. The higher the PEP, the greater the effect on the quality of oxygenation. In our practice we only use standard flowmeters with a maximum delivered O2 flow rate of 15 L/min. We advise to start at 6 L/min and to increase in increments of 3 L/min (Fig. 2). This approach allows to obtain an inspiratory pressure equal to zero (then slightly positive = Inspiratory support) and thus to increase the FiO2 (in case of high inspiratory peak flow due to dyspnoea) and thus to improve the Sa02.
Video: Mounting the antimicrobial HEPA/HME filter on Boussignac-CPAP
Video: CPAP Boussignac Protocol with HEPA filter for Covid19 – by practitioners of AP-HP in Paris
Tutorial: made by the ICU team of the University Hospital Henri-Mondor, AP-HP, Créteil (94000), France.
There are many recommendations circulating regarding COVID-19 infection, most often not to propose the use of NIV (CPAP or mechanical) or HFNO. However, these rules are not based on proven data or high-grade guidelines of recommendations. COVID-19 infection appears to cause an unusual form of acute respiratory failure, with profound hypoxemia but normal pulmonary compliance. This could be due to diffuse atelectasis. However, by definition, patients managed in emergency departments and in EMS are very different from each other, and clinical common sense prevails. Thus, applying a strict rule in the emergency department and/or pre-hospital phase that would require immediate intubation of any patient requiring an O2 flow rate of more than 6 L/min could lead to rapid saturation of ICU capacity and unnecessary intubations. For patients with isolated respiratory failure who are stabilized by moderate amounts of oxygen, it is probably justified to attempt to avoid intubation. The optimal use of non-invasive modes of oxygenation in COVID-19 is currently under investigation. In the context of COVID-19 infection, CPAP may be the mode of choice as a non-invasive oxygenation support for some of the patients. Indeed, it is the non-invasive modality that allows for the most powerful lung recruitment and also has the advantage of avoiding large detrimental tidal volumes. As always, additional evidence is needed.
- Clinical management of severe acute respiratory infection (SARI) when COVID-19 disease is suspected: Interim guidance. WHO, 2020. WHO/2019-nCoV/clinical/2020.4 [lien]
- Wax RS, et al. Practical Recommendations for Critical Care and Anesthesiology Teams Caring for Novel Coronavirus (2019-nCoV) Patients. Can J Anaesth 2020. PMID: 32052373
- Cheung JC, et al. Staff Safety During Emergency Airway Management for COVID-19 in Hong Kong. Lancet Respir Med 2020. PMID: 32105633
- Safe Airway Society. Consensus Statement: Safe Airway Society Principles of Airway management and Tracheal Intubation Specific to the COVID-19 Adult Patient Group. MJA 2020. [Pre Print]
- Bouvet L, et al. Real-time Detection of Gastric Insufflation Related to Facemask Pressure-Controlled Ventilation Using Ultrasonography of the Antrum and Epigastric Auscultation in Nonparalyzed Patients: A Prospective, Randomized, Double-Blind Study. Anesthesiology 2014 ;120(2):326-34. PMID: 24317204.
- Mekontso Dessap A. Frugal innovation for critical care. Intensive Care Med. 2019;45(2):252-254. https://doi.org/10.1007/s00134-018-5391-6
- The Australian and New Zealand Intensive Care Society (ANZICS) COVID-19 Guidelines Version 1. 16 March 2020. https://www.anzics.com.au/wp-content/uploads/2020/03/ANZICS-COVID-19-Guidelines-Version-1.pdf
- Alhazzani W, et al. Surviving Sepsis Campaign: Guidelines on the Management of Critically Ill Adults with Coronavirus Disease 2019 (COVID-19). https://www.sccm.org/getattachment/Disaster/SSC-COVID19-Critical-Care-Guidelines.pdf?lang=en-US
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