[Application effect and influencing factors of early awake prone position in patients with mild-to-moderate acute respiratory distress syndrome].

Objective: To investigate the application effect of early awake prone position in mild-to-moderate acute respiratory distress syndrome (ARDS) patients, and analyze the related factors affecting the prone position outcome.

Methods: A prospective cohort study was conducted. The mild-to-moderate ARDS patients admitted to the emergency department of Yingshang County People's Hospital from January 2020 to June 2023 were enrolled as the research subjects. According to the results of prone tolerance test, the patients were divided into awake prone position group and non-prone position group. All patients were given high flow nasal cannula (HFNC) according to the standard procedures. The patients in the awake prone position group received prone position treatment within 12 hours after admission, in addition to the standard treatment. This could be performed in several times, at least once a day, and at least 2 hours each time. In order to prolong the prone position as much as possible, the patients were allowed to move or keep a small angle side prone. The changes of oxygenation index (PaO₂/FiO₂) at 0, 24, 48, and 72 hours after admission, the rate of intensive care unit (ICU) transfer, the use rate and use time of non-invasive ventilation (NIV), the total hospital stay, and the daily prone position time and 2-hour ROX index [ratio of pulse oxygen saturation/fraction of inspired oxygen (SpO₂/FiO₂) and respiratory rate (RR)] of prone position patients were recorded. The successful termination of HFNC was defined as the successful prone position, and the failure of prone position was defined as switching to NIV or transferring to ICU. Subgroup analysis was performed, and the binary multivariate Logistic regression analysis was used to screen the influencing factors of the early awake prone position outcome.

Results: A total of 107 patients were finally enrolled, with 61 in the awake prone position group and 46 in the non-prone position group. Both groups showed a gradual increase in PaO₂/FiO₂ with prolonged admission time. The PaO₂/FiO₂ at 24 hours after admission in the awake prone position group was significantly higher than that at 0 hour [mmHg (1 mmHg ≈ 0.133 kPa): 191.94±17.86 vs. 179.24±29.27, P < 0.05], while the difference in the non-prone position group was only statistically significant at 72 hours (mmHg: 198.24±17.99 vs. 181.24±16.62, P < 0.05). Furthermore, the PaO₂/FiO₂ at 48 hours and 72 hours after admission in the awake prone position group was significantly higher than that in the non-prone position group. The use rate of NIV in the awake prone position group was significantly lower than that in the non-prone position group [36.1% (22/61) vs. 56.5% (26/46), P < 0.05]; Kaplan-Meier curve analysis further confirmed that the patients in the awake prone position group used NIV later, and the cumulative rate of NIV usage was significantly lower than that in the non-prone position group (Log-Rank test: χ ² = 5.402, P = 0.020). Compared with the non-prone position group, the ICU transfer rate in the awake prone position group was significantly lowered [11.5% (7/61) vs. 28.3% (13/46), P < 0.05], and the HFNC time, NIV time, and total hospital stay were significantly shortened [HFNC time (days): 5.71±1.45 vs. 7.24±3.36, NIV time (days): 3.27±1.28 vs. 4.40±1.47, total hospital stay (days): 11 (7, 13) vs. 14 (10, 19), all P < 0.05]. Of the 61 patients who underwent awake prone positioning, 39 were successful, and 22 failed. Compared with the successful group, the patients in the failure group had a higher body mass index [BMI (kg/m²): 26.61±4.70 vs. 22.91±5.50, P < 0.05], lower PaO₂/FiO₂, proportion of asymptomatic hypoxemia and 2-hour ROX index of prone position [PaO₂/FiO₂ (mmHg): 163.73±24.73 vs. 185.69±28.87, asymptomatic hypoxemia proportion: 18.2% (4/22) vs. 46.2% (18/39), 2-hour ROX index of prone position: 5.75±1.18 vs. 7.21±1.45, all P < 0.05], and shorter daily prone positioning time (hours: 5.87±2.85 vs. 8.05±1.99, P < 0.05). Binary multivariate Logistic regression analysis showed that all these factors were influencing factors for the outcome of awake prone positioning (all P < 0.05), among which BMI [odds ratio (OR) = 1.447, 95% confidence interval (95%CI) was 1.105-2.063] and non-asymptomatic hypoxemia (OR = 13.274, 95%CI was 1.548-117.390) were risk factors for failure of prone position, while PaO₂/FiO₂ (OR = 0.831, 95%CI was 0.770-0.907), daily prone positioning time (OR = 0.482, 95%CI was 0.236-0.924), and 2-hour ROX index of prone position (OR = 0.381, 95%CI was 0.169-0.861) were protective factors.

Conclusions: Early awake prone positioning in patients with mild-to-moderate ARDS supported by HFNC is safe and feasible, reducing the use rate and duration of NIV, lowering the ICU transfer rate, and shortening the hospital stay. High BMI and non-asymptomatic hypoxemia are risk factors for failed prone position, while higher PaO₂/FiO₂ and the ROX index within 2 hours of prone position (the patient's good response to prone position), and prolonged daily prone position can improve the success rate of prone position.