The Use of the Alveolar Gas Meter for Assessment of Gas Exchange Abnormalities in COVID-19

Introduction: COVID-19 pneumonia varies in clinical expression from asymptomatic to severe ARDS. In early COVID-19, some patients have subtle abnormalities and their clinical trajectory is often unclear. We used an alveolar gas meter (AGM), which is designed to measure gas exchange parameters non-invasively while obviating the need for arterial blood gas measurement. The AGM has previously been compared to arterial blood gas analysis with the suggestion that the oxygen deficit by the AGM provides a useful surrogate to the alveolar to arterial oxygen difference (AaDO2) and it is sensitive to minor changes in pulmonary gas exchange. We sought to test the hypothesis that the AGM could be a useful instrument to identify COVID-19 patients at risk of deterioration before obvious respiratory failure had ensued. Methods: We identified 13 patients in the emergency department or non-ICU medical ward who were COVID-19 positive or strongly suspected to be COVID-19 positive. We enrolled patients with informed consent who did not require high dose oxygen. In patients with low dose oxygen, we removed supplemental oxygen with IRB consent to study room air gas exchange. Data were analyzed using Microsoft Excel and an unpaired, two-tailed student's t-test with equal variance was performed to assess for statistical significance between means. Results: Among the 13 patients enrolled, 12 were COVID positive, 5 were discharged home, and 8 were admitted. The AGM readings revealed an oxygen deficit of 55.4 ± 19.9 (mean ± SD) in the hospitalized patients vs. 31.6 ± 14.0 in those sent home (P=0.041). Among the 13 patients, 6 required supplemental oxygen whereas 7 did not. The AGM readings revealed an oxygen deficit of 65.0 ± 9.12 in those requiring supplemental oxygen vs. 30.1 ± 12.7 in those who remained on room air (P=0.00016). There was no statistically significant difference in the end-tidal CO2 between those who were admitted and discharged home or between those who required supplemental oxygen and those who did not. None of our participants required intubation, mechanical ventilation, high flow nasal cannula oxygen, or non-invasive ventilation. Conclusion: The AGM provides an early marker of gas exchange impairment in COVID-19. The data suggest that patients at risk of respiratory failure may be identified early, prior to obvious clinical deterioration in a rapid, non-invasive fashion. Such strategies may be helpful in the triage of patients or for enrolling high risk patients into interventional clinical trials.