Most patients presenting with dyspnoea tend to have low Spo2 on room air and thus require supplemental oxygen to correct hypoxemia. Patients on oxygen support either via face mask, nasal prongs, BiPaP, NIV or invasive mechanical ventilation often have sudden drop in the oxygen saturation which is dangerous requiring immediate action. In this study we try to evaluate different causes for sudden drop in the Spo2 in patients already on oxygen support.