You are caring for a 72-year-old admitted with community-acquired pneumonia. Early in your shift the SpO2 was 94% on 2 L nasal cannula. A few hours later the patient is on 6 L, the SpO2 is 90%, the respiratory rate has climbed to 30, and the patient is increasingly restless and anxious. Over the right lower lobe, where you expect vesicular sounds, you hear bronchial breath sounds with coarse crackles.
The oxygen requirement is climbing and the SpO2 keeps drifting down. What is this trend telling you?
Pneumonia is inflammation and consolidation of lung tissue. The alveoli fill with fluid, cells, and debris, which impairs gas exchange and creates V/Q mismatch and shunting, so the PaO2 falls. This is an oxygenation problem, or hypoxemic respiratory failure. You are not diagnosing it from the chart. You are reading the trajectory and acting on it.
Bronchial breath sounds are normal over the trachea. Hearing them over a peripheral lobe means air has been replaced by fluid, cells, or debris, and solid tissue conducts sound better. That is consolidation.
Because consolidated alveoli are full, blood flows past them without picking up oxygen. That is shunting, and raising the FiO2 alone cannot fully correct it. That is why the trend, not a single reading, drives your judgment.
"The SpO2 is low, so just increase the oxygen." Ask instead: is the patient responding to the oxygen? A rising requirement with a falling number is escalation, not reassurance.
keep asking why