A 71-year-old woman with COPD and hypoxic respiratory failure presents with increased dyspnoea, purulent sputum, and wheeze. She uses a LAMA LABA inhaler at baseline. On arrival, temperature is 38.3 °C, respiratory rate 26 breaths per minute, oxygen saturation 86 percent on room air, and she is using accessory muscles. Which initial management step in the emergency department is most appropriate?