Federico Raimondi, Luca Novelli, Gianmariano Marchesi, Fabrizio Fabretti, Lorenzo Grazioli, Ivano Riva, Chiara Allegri, Roberta Biza, Chiara Galimberti, Ferdinando Luca Lorini, Fabiano Di Marco
{"title":"Worsening of gas exchange parameters at high FiO<sub>2</sub> in COVID-19: misleading or informative?","authors":"Federico Raimondi, Luca Novelli, Gianmariano Marchesi, Fabrizio Fabretti, Lorenzo Grazioli, Ivano Riva, Chiara Allegri, Roberta Biza, Chiara Galimberti, Ferdinando Luca Lorini, Fabiano Di Marco","doi":"10.4081/mrm.2021.759","DOIUrl":null,"url":null,"abstract":"<p><strong>Background: </strong>In COVID-19, higher than expected level of intrapulmonary shunt has been described, in association with a discrepancy between the initial relatively preserved lung mechanics and the hypoxia severity. This study aim was to measure the shunt fraction and variations of PaO<sub>2</sub>/FiO<sub>2</sub> ratio and oxygen alveolar-arterial gradient (A-a O<sub>2</sub>) at different FiO<sub>2</sub>.</p><p><strong>Methods: </strong>Shunt was measured by a non-invasive system during spontaneous breathing in 12 patients hospitalized at COVID-19 Semi-Intensive Care Unit of Papa Giovanni XXIII Hospital, Bergamo, Italy, between October 22 and November 23, 2020.</p><p><strong>Results: </strong>Nine patients were men, mean age (±SD) 62±15 years, mean BMI 27.5±4.8 Kg/m<sup>2</sup>. Systemic hypertension, diabetes type 2 and previous myocardial infarction were referred in 33%, 17%, and 7%, respectively. Mean PaO<sub>2</sub>/FiO<sub>2</sub> ratio was 234±66 and 11 patients presented a bilateral chest X-ray involvement. Mean shunt was 21±6%. Mainly in patients with a more severe respiratory failure, we found a progressive decrease of PaO<sub>2</sub>/FiO<sub>2</sub> ratio with higher FiO<sub>2</sub>. Considering (A-a O<sub>2</sub>), we found a uniform tendency to increase with FiO<sub>2</sub> increasing. Even in this case, the more severe were the patients, the higher was the slope, suggesting FiO<sub>2</sub> insensitiveness due to a shunt effect, as strengthened by our measurements.</p><p><strong>Conclusion: </strong>Relying on a single evaluation of PaO<sub>2</sub>/FiO<sub>2</sub> ratio, especially at high FiO<sub>2</sub>, could be misleading in COVID-19. We propose a two steps evaluation, the first at low SpO<sub>2</sub> value (<i>e.g</i>., 92-94%) and the second one at high FiO<sub>2</sub> (<i>i.e</i>., >0.7), allowing to characterize both the amendable (ventilation/perfusion mismatch), and the fixed (shunt) contribution quote of respiratory impairment, respectively.</p>","PeriodicalId":49031,"journal":{"name":"Multidisciplinary Respiratory Medicine","volume":"16 1","pages":"759"},"PeriodicalIF":2.3000,"publicationDate":"2021-05-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://ftp.ncbi.nlm.nih.gov/pub/pmc/oa_pdf/5e/76/mrm-16-1-759.PMC8168493.pdf","citationCount":"2","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Multidisciplinary Respiratory Medicine","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/10.4081/mrm.2021.759","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"2021/1/15 0:00:00","PubModel":"eCollection","JCR":"","JCRName":"","Score":null,"Total":0}
引用次数: 2
Abstract
Background: In COVID-19, higher than expected level of intrapulmonary shunt has been described, in association with a discrepancy between the initial relatively preserved lung mechanics and the hypoxia severity. This study aim was to measure the shunt fraction and variations of PaO2/FiO2 ratio and oxygen alveolar-arterial gradient (A-a O2) at different FiO2.
Methods: Shunt was measured by a non-invasive system during spontaneous breathing in 12 patients hospitalized at COVID-19 Semi-Intensive Care Unit of Papa Giovanni XXIII Hospital, Bergamo, Italy, between October 22 and November 23, 2020.
Results: Nine patients were men, mean age (±SD) 62±15 years, mean BMI 27.5±4.8 Kg/m2. Systemic hypertension, diabetes type 2 and previous myocardial infarction were referred in 33%, 17%, and 7%, respectively. Mean PaO2/FiO2 ratio was 234±66 and 11 patients presented a bilateral chest X-ray involvement. Mean shunt was 21±6%. Mainly in patients with a more severe respiratory failure, we found a progressive decrease of PaO2/FiO2 ratio with higher FiO2. Considering (A-a O2), we found a uniform tendency to increase with FiO2 increasing. Even in this case, the more severe were the patients, the higher was the slope, suggesting FiO2 insensitiveness due to a shunt effect, as strengthened by our measurements.
Conclusion: Relying on a single evaluation of PaO2/FiO2 ratio, especially at high FiO2, could be misleading in COVID-19. We propose a two steps evaluation, the first at low SpO2 value (e.g., 92-94%) and the second one at high FiO2 (i.e., >0.7), allowing to characterize both the amendable (ventilation/perfusion mismatch), and the fixed (shunt) contribution quote of respiratory impairment, respectively.
期刊介绍:
Multidisciplinary Respiratory Medicine is the official journal of the Italian Respiratory Society - Società Italiana di Pneumologia (IRS/SIP). The journal publishes on all aspects of respiratory medicine and related fields, with a particular focus on interdisciplinary and translational research.
The interdisciplinary nature of the journal provides a unique opportunity for researchers, clinicians and healthcare professionals across specialties to collaborate and exchange information. The journal provides a high visibility platform for the publication and dissemination of top quality original scientific articles, reviews and important position papers documenting clinical and experimental advances.