A pneumonia patient has PaO₂ 55 mmHg. Which intervention is priority?

A PaO₂ of 55 mmHg represents significant hypoxemia — normal is 80–100 mmHg — and is an immediate threat to tissue oxygenation. The priority nursing intervention is to apply supplemental oxygen to correct hypoxemia and prevent end-organ damage. Oxygen delivery must be addressed before any other respiratory intervention can be effective. Increasing oral fluids addresses hydration but does nothing to improve gas exchange in the short term; while hydration supports mucociliary clearance, it is not appropriate as the first response to acute hypoxemia. Incentive spirometry is a useful tool for lung expansion and preventing atelectasis, but it is a secondary measure that should be implemented after oxygenation is stabilized. Encouraging coughing helps clear secretions, which may contribute to the pneumonia, but it is not the immediate priority when the patient is acutely hypoxemic. Using the ABC (airway, breathing, circulation) framework reinforces that oxygenation must be secured first. Once supplemental oxygen is applied and the patient's SpO₂ and PaO₂ improve, the nurse can then proceed with complementary interventions like positioning, incentive spirometry, and hydration.