Extent and Distribution of Parenchymal Abnormalities in Baseline CT-Scans Do Not Predict Awake Prone Positioning Response in COVID-19 Related ARDS

Abstract

Prone positioning is frequently used for non-intubated hypoxemic patients with COVID-19, although conclusive evidence is still lacking. The aim of the present study was to investigate whether baseline CT-scans could predict the improvement in oxygenation in COVID-19 related Acute respira-tory syndrome (ARDS) patients when pronated. Methods: A retrospective study of COVID-19 patients who underwent non-invasive ventilation (NIV) and prone positioning was conducted. Results: Forty-five patients were included. On average, 50% of the overall lung volume was affected by the disease, as observed in the CT-scans, with ground glass opacities (GGOs) and consolidations accounting for 44% and 4%, respectively. The abnormalities were mainly posterior, as demonstrated by posterior/anterior distribution ratios of 1.5 and 4.4 for GGO and consolidation, respectively. The median PaO2/FiO2 ratio during NIV in a supine position (SP1) was 140 [IQR 108–169], which improved by 67% (+98) during prone positioning, on average. Once supine positioning was resumed (SP2), the improvement in oxygenation was maintained in 28 patients (62% of the overall population, categorized as “responders”). We found no significant differences between responders and non-responders in terms of the extent (p = 0.92) and the distribution of parenchymal abnormalities seen in the baseline CT (p = 0.526). Conclusion: Despite the lack of a priori estimation of the sample size, considering the absence of any trends in the differences and correlations, we can reasonably conclude that the baseline chest CT-scan does not predict a gas-exchange response in awake prone-positioned patients with COVID-19 related ARDS. Physicians dealing with this category of patients should not rely on the imaging at presentation when evaluating whether to pronate patients.

Quantitative Computed Tomography and Response to Pronation in COVID-19 ARDS

“…Despite these premises, in classic ARDS, Papazian and colleagues found no correlation between baseline qCT data and PaO 2 /FiO 2 ratio response to pronation 36 . In addition, similarly to what has been observed in non-intubated COVID-19 subjects 18 , we were not able to identify a correlation between baseline qCT-scan characteristics and PaO 2 /FiO 2 ratio response during PP.…”

“…Oxy-R were characterized by higher baseline compliance of the respiratory system (42 ± 11 vs. 32 ± 5 ml/cmH 2 O, p =<.001). The length of the first pronation performed in the ICU was similar in Oxy-R and Oxy-NR (21 [18,24] vs. 24 [22,32] hours, p = .08).…”

“…In addition, the different potential involvement of pulmonary vasculature could justify the broad spectrum of oxygen response to pronation reported in the different studies, going from 35% up to 93% 1,2,18,24,41,42 . Interestingly, and in line with this reasoning, in our population, no difference in qCT characteristics was observed between moderate and severe COVID-19 associated ARDS subjects (Table S8).…”

“…Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome. N Engl J Med 2000;342 (18):1301-1308.…”

“…Recently, Raimondi et al 18 studied awake, non-invasively ventilated COVID-19 subjects and were not able to find any association between the distribution of CT lung lesions and the response in oxygenation to PP.…”