COVID-19 – Use of non-invasive oxygenation CPAP devices in prehospital and intra-hospital emergency care
At a time when COVID 19 epidemic is posing unprecedented challenges to the health sector, it is essential to put in place all the means and techniques necessary to guarantee the safety of patients and health personnel. Greemed in collaboration with our exclusive partner Vygon is proud to provide a series of products needed for health-care professionals and essential service businesses who need them.
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:
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 neighboring 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:
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 another 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 :
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 favorable 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.
Fig. 1: Boussignac-CPAP assembly
The procedure is simple and proceeds as follow (Fig. 1):
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 an 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 us 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.
Fig.2: CPAP installation diagram with an indication of oxygen flow thresholds
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 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.