Comparative evaluation of arterial blood gas in patients with stridor, before and after emergency tracheostomy. The present prospective study was conducted in tertiary care Centre from February 2022 to June 2023 on 42 patients who presented with stridor and underwent emergency tracheostomy in our department. After proper history taking and clinical examination, nonsurgical cause of stridor was ruled out. Patients were then classified on the basis of location of cause of stridor (whether oropharyngeal, hypo-pharyngeal, supra-glottic, glottic or sub-glottic). Immediately an arterial blood gas (ABG) analysis was done, and emergency tracheostomy was performed. Following tracheostomy, ABG analysis was done immediately, after 12 h and after 24 h. The mean age of presentation of stridor in our study was 65.02 ± 3.23 years, with male preponderance (Male: female ratio being 3.66:1). Most common etiology of stridor in our study was glottic carcinoma comprising 50%, and least common etiology of stridor was hypopharyngeal carcinoma, and subglottic stenosis comprising 2.4% each. There was statistically significant normalization of ABG in terms of pH, PO2, PCO2, HCO3. Mean pH, PO2, PCO2, and HCO3 before tracheostomy were 7.31, 74.8, 60.6, and 29.8 respectively. Mean pH, PO2, PCO2, HCO3, immediately after tracheostomy were7.38, 91.3, 48.4, and 27.4 respectively. After 12 h of tracheostomy, mean pH, PO2, PCO2, HCO3 were 7.41, 95.4, 42.7, 25.3 respectively. Mean pH, PO2, PCO2, HCO3 24 h after emergency tracheostomy were 7.441, 95.5, 42.8, 24.6 respectively. Emergency tracheostomy in stridor patients improves the acid base and ventilatory status, by relieving the obstruction as evidenced by statistically significant improvement in arterial blood gas values, and can be used as a diagnostic tool in upper airway obstruction.