Introduction
Since March 2020, the COVID-19 pandemic has increased the influx of severely hypoxemic patients into emergency departments (EDs) all over the world.1 In patients with hypoxemic acute COVID-19 managed in EDs, the most widely used low-flow oxygen therapy to deliver high levels of FIO2 is the non–rebreather mask (NRM).2 However, a study showed the limitations of NRM in delivering adequate levels of FIO2, especially when the breathing pattern is characterized by high inspiratory flow and/or breathing frequency.3 In addition, our group recently showed that when there is an imperfect face mask seal with NRM the measured FIO2 level substantially drops to such an extent that the standard Hudson face mask equalized its performance.4
The double-trunk mask (DTM) is a patent-free device designed to increase FIO2 in adult subjects who receive oxygen via nasal cannula (NC). The DTM is made of an aerosol mask in which 2 corrugated tubings (15 cm length) have been fixed in each of the side holes.5 DTM is placed over the NC, which remains the source of oxygen supply. The 2 corrugated tubings used to make DTM act as an added reservoir for oxygen, maintaining a high level of oxygen concentration around the patient’s face in case of prolonged expiratory time. When DTM is placed over NC, PaO2 increases by approximately 50%, despite unchanged oxygen output.6 A recent publication also demonstrated that addition of DTM over NC can reduce oxygen flows by > 50% in hospitalized subjects with COVID-19.7 Finally, one study determined that DTM was more effective than the addition of a surgical mask over NCs with respect to PaO2.8
However, no study has compared the performance of NRM and DTM in vivo. The aim of our study was thus to compare the performance of DTM and NRM on arterial blood gases in hypoxemic subjects with COVID 19 presenting to ED with acute respiratory distress.
Methods
The inclusion criterion was hypoxemic patients with COVID-19 treated in ED with supplemental oxygen provided by NRM. The diagnosis of COVID-19 was confirmed via polymerase chain reaction testing from nasopharyngeal swab and/or chest computed tomography scan in ED. The exclusion criteria were age < 18 y, COPD or other chronic respiratory diseases with hypercapnia, confusion, and inability to safely obtain arterial blood gas sampling (peripheral arteriopathy, bleeding disorder). Age, height, weight, heart rate, breathing frequency, arterial blood pressure, arterial blood gases, Sequential Organ Failure Assessment (SOFA) score, comfort, and dyspnea with the oxygen delivery system were collected upon admission in ED. The study protocol was approved by Cliniques Universitaires Saint-Luc Ethics Committee and written informed consent was obtained from participants or their authorized representatives. The study was registered in ClinicalTrials.gov (NCT04383821).
Subjects were placed in a semi-recumbent position and received oxygen via NRM at a flow to obtain SpO2 ≥ 90%. Each subject went through a process of 3 phases of 30 min each: phase 1: NRM as defined in the inclusion criteria; phase 2: DTM over NC; phase 3: NRM. Oxygen flow remained unchanged across the phases. Arterial blood gas sampling was taken at the end of phase 1 and phase 2. The other outcomes were taken at the end of each phase. Kolmogorov-Smirnov test was used to analyze distribution of the data. Data are presented as mean ± SD or median (interquartile range [IQR]) as appropriate. Pairwise comparisons were tested with paired t test or Wilcoxon test as appropriate. All tests were 2 sided, and P ≤ .05 was considered significant. Sample size was calculated to be 22 subjects to detect a difference in mean PaO2 change of 6 mm Hg between phase 1 and phase 2 (conservative SD difference 10 mm Hg; 2-sided α level = 0.05; P = .08) to anticipate 15% risk of dropouts due to acute deterioration of health status.
A difference of +6 mm Hg was considered meaningful since it would have meant +10% increase in subjects with a baseline PaO2 60 mm Hg (SpO2 90%). We acknowledge that a difference of 6 mm Hg may fall in the technical error of the measurement. Yet a systematic positive bias from repetitive blood gas measurements is unlikely. We aimed to recruit 25 subjects.
Results
We conducted a multi-center prospective crossover study in EDs in Belgium from May 2020–June 2021. We recruited 25 subjects. Three subjects who signed the informed consent deteriorated before the end of the protocol and were excluded. Twenty-two subjects were, therefore, included in the analysis. Their mean (SD) age was 64.0 (13.6) y; 8 (36%) were female. Mean body mass index was 31.9 kg/m2 (10.0), and mean SOFA score was 4.6 (1.2). All subjects enrolled completed the experimental procedure. No adverse effects were detected. The 22 subjects were subsequently hospitalized, of which 5 (23%) were transferred to ICU (Table 1).
Sociodemographic Description of the Included Participants
Compared to NRM in phase 1, DTM significantly increased PaO2 (70 [60–78] mm Hg vs 85 [67–115] mm Hg, P < .001). SaO2 and SpO2 improved accordingly (Table 2). PaCO2, pH, hemodynamic parameters, comfort, and dyspnea scores did not change between phases 1 and 2 (Table 2). Once NRM was reinstated, all parameters returned to baseline except for breathing frequency.
Comparison of Non–Rebreather Mask Versus Double-Trunk Mask
Discussion
In severely hypoxemic subjects affected by COVID-19-related pneumonia initially treated with NRM, DTM increased PaO2 and decreased breathing. Obstruction by NRM valves can increase entrainment of room air through face mask leaks during inspiration, since gas follows the path of least resistance.9 In clinical practice, it is difficult to keep a face mask completely sealed, especially due to agitation secondary to respiratory distress. Conversely, oxygen reserves in DTM are stored in trunks, without any valve system impeding air flow. Breathing pattern (breathing frequency and tidal volume) can further exaggerate this phenomenon.7 Improvement in blood oxygenation with DTM, compared to NRM, was achieved at the same oxygen flow. Decreased breathing frequency observed in this study is, thereby, probably due to physiologic response to improved blood oxygen levels. PaCO2, pH, dyspnea levels, and mask comfort were not statistically different between both oxygenation systems.
Although the sample size was small, statistical significance was achieved. Only subjects with COVID-19 were included in the study, and thus further studies are warranted to generalize results to other diseases. Although the treatment sequence was not randomized, the double-crossover design reasonably alleviates concerns about timing bias.
In this multi-center study in EDs with subjects with COVID-19, respiratory support with NC combined with DTM improved arterial oxygenation as compared to NRM, despite unchanged oxygen flows. DTM, therefore, appears to be superior in comparison to NRM in low-flow oxygenation.
Footnotes
- Correspondence: Frédéric Duprez PT RT PhD. E-mail: frederic.duprez{at}condorcet.be
The authors have disclosed no conflicts of interest.
Drs Duprez and Bruyneel are co-first authors.
This study was registered on ClinicalTrials.gov, number NCT04383821.
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