ELMO helmet for CPAP to treat COVID-19-related acute hypoxemic respiratory failure outside the ICU: aspects of/comments on its assembly and methodology

We have read with great interest the study by Tomaz et al., ¹ which analyzes the clinical efficacy of a new model of a helmet-CPAP system, designated ELMOcpap, in COVID-19-related acute hypoxemic respiratory failure. We consider that that study published in the last issue of Jornal Brasileiro de Pneumologia represents a great advance regarding CPAP therapy, showing a new model of a helmet-CPAP device, and contributes to extend the use of such devices outside ICUs. However, we believe that there are some clinical and technical aspects that should be discussed.

First, Table 1 ¹ shows that all patients were affected by alkalosis (pH > 7.48) before starting therapy with the device, and the observed RR was not very high and not significantly different from that after its use (28.5 [24.5-34.0] vs. 26.5 [23.5-32.5] breaths/min; p = 0.866). We wonder if the authors considered the possibility of the presence of mixed alkalosis and if these data could be associated with successive helmet-CPAP setting adjustments. We think that this may also predispose patients to self-induced lung injury (P-SILI), ² and we recommend that future studies about ELMOcpap should evaluate, by means of bench or clinical trials, data regarding Vt measurements, ELMOcpap settings, and P-SILI prevention. ³

Second, according to Figure 1 in that study, ¹ we observed that the authors have combined two humidification systems: an active humidifying jar system and a heat and moisture exchanger filter. We consider that this association could predispose to obstruction of the system by condensation, CPAP asynchrony, and, consequently, P-SILI, ² particularly in such patients. Referring to the fact that “None of the research team members or hospital staff acquired COVID-19 during the study,” it has not been stated in which way safety or diffusibility through the interface to prevent the spread of the virus was evaluated. Data about environmental air analysis would have been useful, so as to exclude that no one got infected only because the staff wore personal protective equipment and not because of interface security.

Additionally, an important aspect for a future design could be the measurement of internal helmet gas volume, the use of antiviral filters both on the inspiratory and expiratory ports, and the implementation of an anti-suffocation valve.

Lastly, we observed a great variability of total ELMOcpap therapy time, because the range of daily duration of the sessions was 60-1,230 min, and it is not clear whether defined criteria were established as a guideline, or whether the duration was dependent only on the patient; in addition, it is unclear whether other oxygen therapy options while ELMOcpap was not connected were applied. This is controversial if we consider the level of disease severity and gas exchange at admission showed in Table 2. ¹ We also wonder if the authors designed the ELMOcpap device for continuous noninvasive support application outside the ICU as well, considering that they conducted the study with patients with moderate to severe ARDS, which is evident in Figure 3, ¹ where we find values of Pa_O2/Fi_O2 < 150.

Further clinical trials are needed to evaluate some methodological and technical aspects of this new helmet-CPAP system to be used outside ICUs.