A 68-year-old man with COPD is intubated in the ICU for acute hypercapnic respiratory failure. He is currently on volume-controlled ventilation (VCV) with a tidal volume of 8 mL/kg ideal body weight, respiratory rate 16/min, and FiO₂ 0.6. His ABG shows pH 7.28, PaCO₂ 58 mmHg, PaO₂ 85 mmHg, and HCO₃⁻ 26 mEq/L. Peak inspiratory pressure is 42 cm H₂O. He is triggering the ventilator appropriately and is on minimal sedation. What is the most appropriate next step in management?