A 76-year-old male with a history of obstructive emphysema presents with worsening cough with purulent sputum and dyspnea for 2 weeks, and clouding of consciousness this morning. Physical exam: somnolence, cyanosis, bilateral wet rales, heart rate 116/min with regular rhythm, BP 190/105 mmHg. Neurological examination shows no abnormalities. The most likely diagnosis is: