Prone positioning is a therapeutic strategy for severe Acute Respiratory Distress Syndrome (ARDS). In COVID-19-associated ARDS (CARDS), the application of prone position has shown varying responses, influenced by factors such as lung recruitability and SARS-CoV-2-induced pulmonary endothelial dysfunction. This study aimed to compare the early impact of pronation on lung ventilation-perfusion matching (VQmatch) in CARDS and non-COVID-19 ARDS patients (non-CARDS).

Approach:
This was a two-center, prospective study comparing between CARDS and non-CARDS. Electrical impedance tomography (EIT) was used to compare the VQmatch between supine and early-stage prone positions (~2h). The study identified the areas of Deadspace, shunt, and VQmatch. Within the defined VQmatch region, the global inhomogeneity index (VQmatch-GI) was computed to evaluate the degree of heterogeneity. Paired Wilcoxon signed-rank test and Chi-square test were used in statistical analysis.

Main results:
15 CARDS patients and 14 non-CARDS patients undergoing mechanical ventilation were included. In comparison to the non-CARDS group, the CARDS group exhibited a higher prevalence of diffuse lung disease (15 [100%] vs. 4 [28.6%], CARDS vs. Non-CARDS, p＜0.001), along with elevated SOFA score, PCO2, PEEP, and Ppeak. Among non-CARDS patients, 11/14 demonstrated improved oxygenation, whereas only 5/15 CARDS patients exhibited oxygenation improvement in prone ventilation. In 13/29 patients with oxygenation improvement (defined as above 20% increase in SpO2/FiO2), there was a significant decreased deadspace (21.3 [11.5, 33.1] vs. 9.7 [7.3, 16.9], p=0.039), and VQmatch showed an upward trend. When comparing prone ventilation to supine ventilation, non-CARDS patients showed a significant improvement in overall VQmatch (Supine 65.7 [49.7, 68.5] vs. Prone 67.4 [60.8, 72.6], p=0.019). CARDS patients had a notable decrease in ventral VQmatch (VQmatch_Ventral: Supine 35.0 [26.9, 42.0] vs. Prone 22.7 [12.4, 32.9], p=0.003), and an improvement in dorsal VQmatch (VQmatch_Dorsal: Supine 33.4 [20.4, 39.4] vs. Prone 46.4 [37.4, 48.4], p=0.031), leading to no significant improvement in overall VQmatch. Ten CARDS patients with no improvement in VQmatch had increased shunting and VQmatch-GI.

Significance:
In non-CARDS patients, the improvement in oxygenation and VQmatch following prone positioning exhibits a consistent pattern. Conversely, in CARDS patients, the impact of prone positioning reveals considerable individual variability. This study indicates that the response to short-time prone ventilation can vary in ARDS patients with different etiologies.

Trial registration: NCT05816928, 04/17/2023, retrospectively registered.
Keywords: Acute respiratory distress syndrome; COVID-19; Electrical impedance tomography; Prone position; oxygenation; ventilation-perfusion matching.
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