A 55-year-old woman is intubated and ventilated for severe community-acquired pneumonia. On day 3, the nurse notes sudden high-pressure alarms on the ventilator. Examination reveals absent breath sounds on the left, tracheal deviation to the right, and haemodynamic instability with systolic blood pressure 75 mmHg and heart rate 130 bpm. SpO2 has dropped to 82%. What is the most appropriate immediate action?