A 44-year-old woman with severe pneumocystis pneumonia (PCP) and HIV is admitted to ICU requiring intubation. She weighs 55 kg. ABG pre-intubation on 15 L/min reservoir mask: pH 7.30, PaO2 6.0 kPa, PaCO2 4.0 kPa, HCO3 18 mmol/L, lactate 3.5 mmol/L. Which is the most appropriate initial ventilation strategy?