A 63-year-old woman with COPD presents with increased dyspnea, sputum volume, and purulence for 2 days. She uses home oxygen at 2 liters per minute. On exam, she is tachypneic with diffuse wheezes. Arterial blood gas on oxygen shows pH 7.32, PaCO2 58 mm Hg, PaO2 60 mm Hg. What is the most appropriate next step in ventilatory management?