Diaphragm ultrasound for predicting weaning success in post-cardiac surgery acute respiratory distress syndrome patients: a prospective observational study in China

To explore the value of the diaphragm thickness fraction (TF) and diaphragm mobility (DM) measured by ultrasound for predicting ventilator withdrawal success in patients with acute respiratory distress syndrome (ARDS) after cardiac surgery. This study included 246 patients undergoing the spontaneous breathing trial. Diaphragmatic function was evaluated by ultrasound, including the diaphragm thickness at the end of calm breathing (thickness of the diaphragm at functional residual capacity [TdiFRC]) and the maximum diaphragm thickness at the end of inspiration (thickness of the diaphragm at full vital capacity [TdiFVC]); TF=(TdiFVC-TdiFRC)/TdiFRC×100%. DM, the oxygenation index (the ratio of the partial pressure of arterial oxygen to the fraction of inspired oxygen), and the rapid shallow breathing index (RSBI) were measured. Successful liberation from mechanical ventilation was observed in 209 patients. There were no significant differences in the TdiFRC (0.3±0.1 cm vs. 0.3±0.1 cm) or TdiFVC (0.3±0.1 cm vs. 0.2±0.1 cm) between the ventilator withdrawal success group and the ventilator withdrawal failure group (P>0.05). The TF was greater in the ventilator withdrawal success group than in the ventilator withdrawal failure group (40.8%±15.8% vs. 37.7%±9.2%, P<0.01). DM in the ventilator withdrawal success group was greater than that in the ventilator withdrawal failure group (1.5±0.5 cm vs. 1.2±0.4 cm, P=0.040). The RSBI was lower in the ventilator withdrawal success group than in the ventilator withdrawal failure group (74.3±25.6 breaths·min-1·L -1 vs. 89.9±34.5 breaths·min-1·L -1, P<0.01). Diaphragmatic ultrasound can be used to predict the success of ventilator withdrawal in patients with ARDS.