Weaning procedure
The patients were assessed daily for weaning. If they fit weaning criteria, ERT with pressure support ventilation (PSV) for 2 hours was performed according to our institutional protocol. The PSV settings were set as: PEEP at 5 cm H2O, PS adjusted minimally to overcome endotracheal tube resistance and generate a tidal volume of 4–8 ml/kg, and fiO2 at 40%. The ERT failure criteria were as follows: 1) clinical findings: diaphoresis, nasal flaring, increased work of breathing, tachypnea (>50% increase compared to baseline), tachycardia (>20% increase compared to baseline), apnea, arrythmia, hypotension, increase of >10mmHg of end-tidal carbon dioxide compared to the baseline value 2) laboratory findings:, arterial blood pH <7.32, decrease in arterial pH by 0.07 or more compared to baseline, decrease in SpO2 more than 5%3. Patients who did not fail ERT had a diaphragmatic ultrasound and were extubated right away. Successful weaning (SW) was defined as patients who did not require mechanical ventilation (invasive or non-invasive) within 48 hours of extubation, whereas failed extubation (FE) was defined as patients who required re-intubation or non-invasive mechanical ventilation within 48 hours of extubation. Another intensivist who was blinded to DUS measurements made the decision regarding the need for reintubation or non-invasive ventilation following extubation.