A 58-year-old man is admitted to the ICU with community-acquired pneumonia and bilateral infiltrates on chest radiograph. He is intubated and ventilated. His weight is 70 kg (IBW 70 kg). Current ventilator settings: Volume-controlled ventilation, tidal volume 420 mL, PEEP 12 cmH2O, FiO2 0.7, respiratory rate 28/min. ABG: pH 7.28, PaO2 8.5 kPa, PaCO2 6.8 kPa, HCO3 22 mmol/L, BE -4, lactate 2.1 mmol/L. Plateau pressure is 32 cmH2O. What is the most appropriate next ventilator adjustment?