An elderly gentleman with background of pulmonary fibrosis on long term oxygen therapy,hypertension, type 2 diabetes mellitus, hypercholesterolaemia, and previous ischaemic heart disease, was admitted due to 1 week history of productive cough with greenish sputum, intermittent fever, increasing in shortness of breath. On admission, patient's oxygen saturation was around 84% on room air, with increased in respiratory rate to around 30 per minute. Examination of lung show left basal coarse crackles, with reduced in air entry on left base. Chest x-ray confirmed left lower lobe consodilation, on background of fibrotic changes. Arterial blood gas showed that patient was in type 1 respiratory failure (reduced pO2, with normal pCO2). Patient's oxygen saturation was slightly improved to around 87% on 100% of oxygen. What is your diagnosis, and what anitbitioc to be given ?? Given that patient was still tachypnoea , and low oxygen saturation on 100% oxygen, what will be your next step to improve his respiratory status ??