A 68-year-old male with COPD presents to the ICU with acute respiratory failure (pH 7.22, PaCO₂ 65 mmHg, PaO₂ 55 mmHg on FiO₂ 0.6). After 2 hours of non-invasive ventilation (NIV) failure, the decision for intubation is made. On laryngoscopy, the vocal cords are visualized (Cormack-Lehane Grade 2), but the tube passes easily into the trachea. Immediately after tube placement, end-tidal CO₂ (ETCO₂) is 0 mmHg and there is no condensation in the tube. Breath sounds are absent bilaterally. What is the next step in management?