A patient is newly intubated with normal breath sounds on one side and diminished on the other. What is the likely cause?

The scenario describes a patient who has been intubated and exhibits normal breath sounds on one side while having diminished breath sounds on the other. This clinical presentation is most consistent with intubation in the right mainstem bronchus.

When an endotracheal tube is placed, it may inadvertently enter the right mainstem bronchus instead of the trachea. The right mainstem bronchus is anatomically straighter and shorter than the left, making it more likely for the tube to advance further into this bronchus. As a result, ventilation will primarily occur in the right lung, causing breath sounds to be normal on that side. Conversely, the left lung will receive inadequate ventilation, leading to diminished breath sounds on that side due to reduced airflow.

While pneumothorax could also account for diminished breath sounds, it is less likely to be the immediate cause in a newly intubated patient where breath sounds were previously normal. Congestive heart failure typically presents with bilateral breath sounds on exam, not asymmetric findings as described. Therefore, the explanation for the clinical finding of diminished breath sounds on one side aligns most logically with intubation in the right mainstem bronchus.