OBJECTIVES: Bacterial infections are the major cause of acute exacerbation of COPD (AE-COPD). The relationship between lung func-tions and respiratory failure (arterial blood gas parameters) with the etiology of AE-COPD has not been clearly understood. We conductedthis study to determine the bacterial profile in AE-COPD and to identify the associated risk factors and drug sensitivity pattern.MATERIAL AND METHODS: Seventy-two patients hospitalized for AE-COPD were prospectively evaluated. Quantitative sputum culture,blood gas analysis, and drug sensitivity testing were performed at the time of admission, and pulmonary function testing was performed 6weeks after discharge as per standard guidelines.RESULTS: Bacterial pathogens were isolated in 34 (47.22%) cases. Pathogens isolated were Pseudomonas aeruginosa (38.23%), Klebsiellapneumoniae (29.41%), Staphylococcus aureus (23.53%), Streptococcus pneumoniae (5.88%), and Acinetobacter spp. (2.94%). Isola-tion of bacterial pathogen was observed in patients with advancing age (p=0.02), frequent exacerbations (p<0.001), systemic steroid use(p=0.005), and deranged lung function (p=0.02). Binary logistic regression analysis revealed that higher partial pressure of carbon dioxide(PaCO2) was independently associated with isolation of K. pneumoniae (p=0.025) and P. aeruginosa (p=0.001). Additional independentfactors that favor isolation of K. pneumoniae were age >55 years (p=0.017) and systemic steroid use (p=0.017). Antibiotic sensitivity test-ing showed that ciprofloxacin and piperacillin/tazobactum were effective in 27/34 (79.41%) of isolates followed by gentamycin in 26/34(76%).CONCLUSION: Hypercapnic respiratory failure is an independent risk factor for isolation of K. pneumoniae and P. aeruginosa in additionto advanced age and systemic steroid use. These findings may be an important adjunct in deciding the initial antibiotic therapy.