Worsening of gas exchange parameters at high FiO2 in COVID-19: misleading or informative?

IF 2.3
Multidisciplinary Respiratory Medicine Pub Date : 2021-05-25 eCollection Date: 2021-01-15 DOI:10.4081/mrm.2021.759
Federico Raimondi, Luca Novelli, Gianmariano Marchesi, Fabrizio Fabretti, Lorenzo Grazioli, Ivano Riva, Chiara Allegri, Roberta Biza, Chiara Galimberti, Ferdinando Luca Lorini, Fabiano Di Marco
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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.

Abstract Image

Abstract Image

COVID-19高FiO2下气体交换参数恶化:误导还是提供信息?
背景:在COVID-19中,已经描述了高于预期水平的肺内分流,这与初始相对保存的肺力学与缺氧严重程度之间的差异有关。本研究旨在测定不同FiO2浓度下的分流率、PaO2/FiO2比值及肺泡-动脉氧梯度(a - O2)的变化。方法:于2020年10月22日至11月23日在意大利贝加莫Papa Giovanni XXIII医院COVID-19半重症监护病房住院的12例患者中,采用无创系统测量自主呼吸时的分流。结果:男性9例,平均年龄(±SD) 62±15岁,平均BMI 27.5±4.8 Kg/m2。全身性高血压、2型糖尿病和既往心肌梗死分别占33%、17%和7%。平均PaO2/FiO2比值为234±66,11例患者出现双侧胸片受累。平均分流率为21±6%。主要在较严重的呼吸衰竭患者中,我们发现PaO2/FiO2比率随着FiO2的升高而逐渐降低。考虑(a -a - O2),我们发现随着FiO2的增加有统一的增加趋势。即使在这种情况下,患者越严重,斜率也越高,这表明由于分流效应导致的FiO2不敏感,我们的测量结果加强了这一点。结论:单纯依靠PaO2/FiO2比值评估,特别是在高FiO2情况下,可能会误导COVID-19。我们提出了两步评估,第一步是低SpO2值(例如92-94%),第二步是高FiO2值(即>0.7),从而分别表征可修正(通气/灌注失配)和固定(分流)呼吸损伤的贡献引用。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Multidisciplinary Respiratory Medicine
Multidisciplinary Respiratory Medicine Medicine-Pulmonary and Respiratory Medicine
自引率
0.00%
发文量
23
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.
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