Objective To evaluate the therapeutic effect of high-flow nasal cannula oxygen therapy combined with prone position on mild to moderate acute respiratory distress syndrome(ARDS) by pulmonary ultrasound.

Methods Thirty-two patients with mild to moderate ARDS were enrolled as study subjects who received high flow oxygen therapy combined with prone position.The arterial blood gas, pulmonary ultrasonic score (LUS), hemodynamic indexes (heart rate, mean arterial pressure) before and after prone position were collected.When the percutaneous oxygen saturation(SpO₂)of patient elevated more than 20% after prone positioning was defined as a positive response.According to this criteria, all patients were divided into responsive group (n=22) and non-responsive group (n=10).The changes of general clinical indexes, ultrasonic score of the two groups were compared.

Results A total of 32 patients were included.The proportion of pulmonary lesions in the responsive group was significantly lower than that in the non-responsive group, and the levels of interleukin-6 and body mass index in the responsive group were significantly higher than those in the non-responsive group (P < 0.01).There were statistically significant differences in PaO₂, PaO₂/FiO₂, RR, LUS_ventral, and LUS_dorsalbetween before and after prone position (P < 0.01).The dorsal score of the responsive group before prone position was higher than that of the non-responsive group, while the ventral score was lower than that of the non-responsive group (P < 0.01).The dorsal and ventral scores of the responsive group after prone position were lower than those of the non-responsive group (P < 0.01).

Conclusions Conscious prone position can improve oxygenation in mild to moderate ARDS.Pulmonary ultrasound cannot predict oxygenation after treatment in prone position, but can monitor ventilation changes during prone position.