What is the likely cause of diminished breath sounds on the left side in an intubated adult patient?

• A. Pleural effusion
• B. Left-sided fluid consolidation
• C. Left-sided pneumothorax
• D. Intubation of the right mainstem bronchus

Answer: (D)

Diminished breath sounds on the left side in an intubated adult patient are likely caused by intubation of the right mainstem bronchus. When the endotracheal tube is inadvertently positioned too far down the right mainstem bronchus, it can lead to inadequate ventilation of the left lung. This is because the tube effectively bypasses the left mainstem bronchus, causing minimal or no air to enter the left lung, which results in reduced or absent breath sounds on that side.

This phenomenon occurs because the placement of the tube directly influences which lung receives airflow. If the left lung is not being ventilated properly due to this misplacement, you will notice diminished or even absent breath sounds on the left side. Recognizing this allows healthcare providers to take corrective action, such as repositioning the endotracheal tube, to ensure adequate ventilation of both lungs.