Effect of prone position on ventilation-perfusion matching in patients with moderate to severe ARDS with different clinical phenotypes.

Background: ARDS is a heterogeneous syndrome involving different subphenotypes with different clinical features and different responses to treatment strategies. The prone position (PP) is an effective treatment for ARDS; however, whether the effects of prone positioning vary among ARDS patients with different subphenotypes remains unknown.

Objectives: To evaluated the impact of PP on ventilation-perfusion matching(VQ matching) by contrast-enhanced Electrical impedance tomography (EIT) in ARDS patients with different subphenotypes.

Methods: This was a prospective, observational study at the medical ICU of Zhongda Hospital, Southeast University. ARDS patients undergoing mechanical ventilation were screened and allocated to different subphenotypes based on lung morphology (focal/non-focal) and D-dimer level (low/high D-dimer). EIT was used in the supine position and 3 h, 6 h, and 12 h after the PP during the first PP session.

Results: From July 1, 2021, to July 1, 2022, 25 patients were included in this study. 10 patients (40%) were focal ARDS, and 15 were non-focal ARDS based on baseline morphology. 12 patients (48%) were high D-dimer ARDS, and 13 were low D-dimer ARDS based on baseline D-dimer levels. PaO2/FiO2 increased significantly 3 h after prone positioning in focal ARDS patients (130.30[109.94-147.30] vs. 213.50[176.00-256.50] mmHg, p < 0.001), while the effect of improved oxygenation was not apparent until 6 h after prone positioning in non-focal ARDS patients (104.60[95.20-127.00] vs. 190.20[160.10-213.20] mm Hg, p < 0.001). VQ matching improved after 3 h in the prone position in the focal ARDS group (69.93 ± 6.69 vs. 78.22 ± 5.07, p = 0.006) but improved after only 6 h in the prone position in the non-focal ARDS group (67.32 ± 4.78 vs. 78.70 ± 5.93, p < 0.001). In ARDS patients with varying levels of D-dimer, increased PaO2/FiO2 (126.60[99.30-146.20] vs. 185.20[112.10-236.00] mmHg, p = 0.013) and improved VQ matching (67.60 ± 4.60 vs. 72.97 ± 6.48, p = 0.023) were observed at 3 h in the PP in patients with low D-dimer ARDS. In contrast, increased PaO2/FiO2(105.20[95.20-124.10] vs. 195.2[183.20-213.20], p < 0.001) and improved VQ matching (67.19 ± 6.70 vs. 72.50 ± 6.37, p < 0.001) were revealed only after 6 h in the prone position in high D-dimer ARDS patients.

Conclusions: For moderate to severe ARDS patients, non-focal and high D-dimer ARDS patients need longer PP to improve oxygenation and VQmatching than the focal and low D-dimer patients.

Clinical Trial Registration: This was a prospective, observational study registered in the Chinese Clinical Trial Registry (ChiCTR2200055442, https://www.chictr.org.cn/ ), on June 30, 2021.