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 <
0.002), 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 <
0.002). 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 <
0.002). 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 <
0.002) and improved VQ matching (67.19 ± 6.70 vs. 72.50 ± 6.37, p <
0.002) 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.