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Performance of EasyBreath ® Decathlon Snorkeling mask for Delivering Continuous Positive Airway Pressure

Background: During the COVID-19 pandemic, the need for noninvasive respiratory support devices has dramatically increased, sometimes exceeding hospital capacity. The full-face Decathlon snorkeling mask, EasyBreath ® (EB ® mask), has been adapted to deliver continuous positive airway pressure (CPAP) as an emergency respiratory interface. We aimed to assess the performance of this modified EB ® mask. Methods: CPAP set at 5, 10, and 15 cmH 2 O was delivered to 10 healthy volunteers with a high-flow system generator set at 40, 80, and 120 L min -1 and with a turbine-driven ventilator during both spontaneous and loaded (resistor) breathing. Inspiratory CO 2 partial pressure (PiCO 2 ), pressure inside the mask, breathing pattern and electrical activity of the diaphragm (EAdi) were measured at all combinations of CPAP/flows delivered, with and without the resistor. Results: Using the high-flow generator set at 40 L min -1 , the PiCO 2 significantly increased and the system was unable to maintain the target CPAP of 10 and 15 cmH 2 O and a stable pressure within the respiratory cycle; conversely, the turbine-driven ventilator did. EAdi significantly increased with flow rates of 40 and 80 L min -1 but not at 120 L min -1 and with the turbine-driven ventilator. Conclusions: EB ® mask can be safely used to deliver CPAP only under strict constraints, using either a high-flow generator at a flow rate greater than 80 L min -1 , or a high-performance turbine-driven ventilator.


INTRODUCTION
Hospitals and physicians worldwide are facing a new health emergency as a consequence of the coronavirus diseases 2019 (COVID-19) pandemic 1 that has spread enormously worldwide 2 , placing an extraordinary demand on the health-care systems.
Healthcare organizations have proactively implemented several strategies to supply shortages of equipment as demand surges, rationing life-saving treatments such as using shared mechanical ventilation 6 , establishing ventilator lottery or ventilator triage policies 7,8 , and increasing the use of NRS 9 . To address the high demand for NRS equipment exceeding the capacity, Food and Drug Administration issued an emergency policy allowing the use of home respiratory devices, such as Continuous Positive Airway Pressure (CPAP), as an alternative to life-saving ventilators 10 .
The need to ensure the availability of the highest possible number of CPAP devices also led a group of engineers from northern Italy to build an "emergency ventilator mask", converting full face snorkeling masks into interfaces that can be used to apply CPAP therapy 11 . Nevertheless, innovative and potentially life-saving products not previously tested and approved for clinical use can cause serious adverse effects.
Thus, the present study aimed to assess the technical performance of a modified commercial surface snorkeling mask that has been used in COVID-19 patients in delivering CPAP. The aim of this study was to evaluate the stability of pressure generated and the amount of carbon dioxide (CO 2 ) rebreathing inside the mask during spontaneously and resistive loaded breathing in healthy volunteers. All rights reserved. No reuse allowed without permission.
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RESULTS
Ten healthy volunteers (eight males and two females), with age comprised between 27 and 45 years old and a mean body mass index (BMI) of 24 kg/m 2 completed the study.
None of the subjects complained about discomfort or fogging of the interface.
The FiO 2 delivered during CPAP with the flow generator was between 31% and 34%, depending on the flow/PEEP combination. During CPAP delivered with the turbinedriven ventilator, the FiO 2 ranged from 30 to 35%.
The PiCO 2 ranged from 0 to 7 mmHg, depending on the flow/CPAP level combination used (p<0.01, ANOVA for repeated measurements), as shown in Table 1.
The highest PiCO 2 was recorded at 40 L min -1 of fresh gas flow with CPAP 15 cmH 2 0 and it decreased progressively to 0 (undetectable) as the fresh gas flow increased up to 120 L min -1 or using the turbine-driven ventilator, independently of the CPAP level.
The pressures inside the mask at different flows/PEEP are shown in Table 2 and Figure 3. Target CPAP was not achieved when the oxygen-driven flow generator delivered 40 L min -1 . Only the highest flow tested (120 L min -1 ) allowed the achievement of all the CPAP levels tested (5,10,15 cmH 2 O), even if some over-treatment was obtained at CPAP 5 and 10 cmH 2 O (+ 119% and + 35%, respectively). By contrast, the turbine-driven ventilator allowed the maintenance of target CPAP levels throughout the protocol. Table 2 also shows actual CPAP partitioned between the inspiratory and expiratory phase, as referenced to target CPAP. Only the turbine ventilator succeeded in keeping the actual CPAP level close to its target value both at end-expiration and at end-inspiration for all the CPAP levels tested, the pressure difference between end-inspiration and endexpiration being maintained within 2 cmH 2 O. Statistically and clinically worse was the performance of the high-flow generator in this task. As a matter of fact, at a flow of 40 L min -1 , neither end-inspiratory nor end-expiratory pressures reached the target CPAP. In All rights reserved. No reuse allowed without permission.
(which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.
The copyright holder for this preprint this version posted November 3, 2020. ; https://doi.org/10.1101/2020.10.28.20221317 doi: medRxiv preprint contrast, at 80 and 120 L min -1 , the actual pressure was above its target level at endexpiration and below it at end-inspiration, with the difference between these two conditions being well above 2 cmH 2 O, Table 2. Similar results were obtained for both loaded and unloaded breathing, Table 2.
The respiratory pattern (flows, volume, and respiratory timing) and the EAdi recorded at baseline and at different experimental conditions, with and without the use of the resistor, are shown in Table S1 and Figure 4. In comparison to baseline, minute ventilation remained stable with the CPAP mask at any level of pressure applied during unloaded breathing. By contrast, it significantly decreased during loaded breathing because of a significant reduction of tidal volume. Respiratory rate remained constant throughout the protocol (Table S1).
Diaphragmatic electrical activity increased with any CPAP level compared to baseline, either in terms of EAdi Insp AUC and EAdi/V T (Fig. 4). During loaded breathing, EAdi increased by a similar amount in all the conditions tested. All rights reserved. No reuse allowed without permission.
(which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

DISCUSSION
The present study showed that the use of a modified EB ® mask coupled with a highflow generator: 1) induces substantial CO 2 rebreathing when set at a flow rate below 80 L min -1 , 2) fails to achieve CPAP levels higher than 5 cmH 2 O if set at a flow rate of 40 L min -1 and 3) increases diaphragm's electrical activation (and, hence, diaphragmatic energy expenditure) due to pressure instability along the respiratory cycle. These adverse effects disappear using high flows flushing the CPAP circuit (> 80 L min -1 ) or a high-performance turbine-driven ventilator set in CPAP mode.
The use of repurposed devices to fend off the shortage of ventilators during the current COVID-19 pandemic, without prior evidence of efficacy, is an issue of increasing concern 12 . Manufacturers are allowed to market many medical devices without the need to provide proof of their effectiveness, especially in urgent unusual circumstances like the COVID-19 pandemic 13 . Indeed, clinicians may be forced to adopt unregistered interfaces, such as the popular Decathlon EB ® mask, to deliver ventilatory support to patients with little or no prior tests of performance. To the best of our knowledge, this is the first study that fills this knowledge gap after the introduction of the modified Decathlon EB ® mask for CPAP delivery.
The use of CPAP in acute hypoxemic respiratory failure has the principal aim to improve gas-exchange increasing the end-expiratory lung volume (EELV) and avoiding at the same time the inspiratory elastic threshold-load imposed by the increased EELV 14 .
This task has been effectively accomplished by non-invasively applied CPAP 15,16 .
However, some interfaces can provoke CO 2 rebreathing if misused, thus impairing treatment effectiveness 17 .

CO 2 rebreathing
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The copyright holder for this preprint this version posted November 3, 2020. ; https://doi.org/10.1101/2020.10.28.20221317 doi: medRxiv preprint EB ® mask has a wide dead-space (about 800-900 ml), and thus, given a fixed CO 2 production, it requires high flows to wash-out the exhaled CO 2 completely. In accordance with previous findings obtained with other high dead-space interfaces 17 only CPAP flow rate of 120 L min -1 or flows guaranteed by a high-performance turbine-driven ventilator completely flushed out CO 2 . Thus, in case of emergency use of the EB ® mask, the first caveat is to use very high flows of fresh gas (about fourfold the peak inspiratory flow) in the circuit, whatever its source.

Effectiveness in achieving target CPAP
An ideal CPAP system, by definition, should provide a target positive airway pressure through the respiratory cycle to improve alveolar recruitment and gas exchange.
This was not the case of the EB ® mask. Our data show that although the pressure inside the mask never dropped below zero during the inspiratory phase, it always remained far below the set CPAP level when using a fresh gas flow of 40 L min -1 . On the other hand, during the expiratory phase, the pressure level recorded at the highest rate of fresh gas flow (120 L min -1 ) overcame the set CPAP level, at least at 5 and 10 cmH 2  However, old devices performed worse than high flow generators in delivering stable CPAP levels, mainly because of the demand-valve technology 18 . The newer generation of ventilators has complex flow algorithms that allow for a more aggressive flow modulation and delivery flows using single circuits with intentional leaks designed to stabilize airway pressure and lessen the imposed work of breathing 15 . This was the case in our study when CPAP was delivered with the turbine-driven ventilator provided with an intentional All rights reserved. No reuse allowed without permission.
(which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

Diaphragmatic activity and effort
An ideal CPAP system should provide a constant positive airway pressure throughout the respiratory cycle to avoid negative effects on the work of breathing 19,20 since large pressure swings around the set PEEP level are associated with increased respiratory efforts 21 . Our study showed that end-inspiratory to end-expiratory pressure swing was clinically relevant (above 3 cmH 2 0) at all set levels of CPAP and flows when using the high flow generator with a flow rate lower that 80 L min -1 . We observed this phenomenon notwithstanding the presence of a pressure stabilizer (reservoir bag) and a threshold PEEP valve in the CPAP circuit that should maintain the pressure stable whatever is the flow passing through it. Pressure swings occurring across target CPAP levels imply wasted patients' respiratory effort spent against CPAP device, ineffective in producing flow and volume 18 . As a matter of fact, EAdi inspiratory activity and, hence, EAdi increase can be due to CPAP system-induced increased workload, on a CO 2 rebreathing-induced increase of respiratory drive, or a combination of both. The inspiratory EAdi-time product (EAdi InspAUC) increased by 45% during CPAP application and only 35% when it was normalized for V T , indicating that both the above-quoted mechanisms contributed to the overall increase of EAdi activity during EB ® mask CPAP delivery, as compared to spontaneous breathing. The increase of diaphragmatic electrical activity (and effort) disappeared during CPAP set at the highest flow tested (120 L min -1 ) and during All rights reserved. No reuse allowed without permission.
(which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.
The copyright holder for this preprint this version posted November 3, 2020. ; This study should be a warning sign against the indiscriminate use of tools to deliver noninvasive respiratory support without rigorous tests of performance.

Strengths and limitations
The main strength of our study is the rigorous evaluation of several parameters of performance (i.e. PiCO 2, Pmask, EAdi) at three different levels of flow, recreating the setup used in clinics for noninvasive ventilatory support in COVID-19 patients.
The present study has several limitations. First, this was a proof-of-concept study performed in healthy volunteers; therefore, it may not reflect the dynamic nature of ventilation parameters during severe acute respiratory syndrome. However, simulating loaded breathing, we partially overcame this limitation. Furthermore, we did not compare the new device against a 'gold standard'. Thus, up to now, it is only clear that the EB ® mask works properly only under strictly controlled conditions. Still, it is impossible to state whether it is inferior/superior to reference interfaces. Finally, the PiCO 2 was stable during the conditions tested, but the recordings lasted only 2 minutes each. Therefore, we cannot ensure that these values would have remained stable for a longer period.

CONCLUSION
The modified Decathlon's EB ® mask should be used for emergency use to deliver CPAP only under strict constraints, using a high-flow generator at a flow rate greater than 80 L min -1 , or with a high-performance turbine-driven ventilator.
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(which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.
The copyright holder for this preprint this version posted November 3, 2020. ; 1 1

Study Design
We designed a physiological study involving ten healthy volunteers recruited among physicians at the Department of Anesthesia and Critical Care, Policlinico "G. Martino," University of Messina, Italy, in June 2020. The study was approved by the Ethics committee of Policlinico G. Martino, Messina, Italy (32-30 27/05/2020). All the study participants provided written informed consent.

Experimental set-up and Study devices
The experimental set-up is illustrated in Figure 1. shown in Figure S1. The internal volume was measured by filling the mask with water when applied to the volunteers' face, as previously described 27 , and amounted to 880±11 ml.
To allow measurements, the experimental setting included the following items (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.
The copyright holder for this preprint this version posted November 3, 2020. All the instruments underwent testing and calibration according to the manufacturers' specifications before performing all the measurements.
Each volunteer was studied placed comfortably in a semi-recumbent position and performed all the tests on the same day in random order. Volunteers were first allowed to adapt to CPAP breathing before the recordings.
At baseline, two, 120 seconds each, recordings of breathing pattern and EAdi were carried out without the mask. The first one during quiet unloaded breathing, and the second while breathing through an inline resistor (connected to the mouthpiece) made with an endotracheal tube connector with an inner diameter of 5 mm, to simulate an increase of respiratory load. All rights reserved. No reuse allowed without permission.
(which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.
The copyright holder for this preprint this version posted November 3, 2020. ; https://doi.org/10.1101/2020.10.28.20221317 doi: medRxiv preprint After tightly fitting to the volunteers' face the modified EB ® mask 11  A 120 seconds-trial was recorded for each session for off-line analysis. No instructions were given to the subjects regarding the breathing pattern to adopt.

Data analysis
A Matlab (version 9.7.0.1190202, The MathWorks Inc., Natick, Massachusetts, USA) automatic procedure was developed to find maximal and minimum EAdi ( Figure 2) and pressure for each breath. The EAdi-time product, measured as the EAdi curve area from the beginning to the end of an inspiratory cycle (EAdi Insp AUC ), was calculated All rights reserved. No reuse allowed without permission.
(which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.
The copyright holder for this preprint this version posted November 3, 2020. ; 1 4 ( Figure 2). The EAdi Insp AUC was then normalized for the tidal volume (V T ), (EAdi /V T ).
Average end-expiration and end-inspiration peak pressures were calculated for every recording session. The same was also done for the EAdi max , EAdi Insp AUC, and EAdi /V T .
For each recording session, the average delta pressure inside the mask at the endexpiration (ΔPmask Exp = Pmask end-expiratory -CPAP Level) and end-inspiration (ΔPmask Insp = Pmask end-inspiratory -CPAP Level) were computed. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.
The copyright holder for this preprint this version posted November 3, 2020. ; https://doi.org/10.1101/2020.10.28.20221317 doi: medRxiv preprint p v a l u e All rights reserved. No reuse allowed without permission.
(which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.
The copyright holder for this preprint this version posted November 3, 2020.   Abbreviations: EAdi, electrical diaphragm activity; EAdi max , peak electrical diaphragm activity; EAdi min , electrical diaphragm activity; EAdi Insp AUC , electrical diaphragm activity area of the inspiratory phase; EAdi Tin, inspiratory time derived from electrical diaphragm activity; EAdi Ttot, total respiratory time derived from electrical diaphragm activity.

Figure 3: Pressure recorded inside the mask.
Upper whiskers represent the mean pressure at end-expiration; Lower whiskers represent the mean pressure at end-inspiration; Circles represent the mean pressure; Redline represents the set CPAP level.

Figure 4: Electrical diaphragm effort.
EAdi/V T, electrical diaphragm activity area of the inspiratory phase normalized for the tidal volume (V T ); EAdi Insp AUC, electrical diaphragm activity area of the inspiratory phase.
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(which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.
The copyright holder for this preprint this version posted November 3, 2020.
(which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.
The copyright holder for this preprint this version posted November 3, 2020. ;