An endotracheal tube inserted too far will most likely rest in?

• A. Right mainstem bronchus
• B. Left mainstem bronchus
• C. Lung parenchyma
• D. Carina

Answer: (A)

An endotracheal tube that is advanced too far tends to slip into a main bronchus rather than stay in the trachea. The right mainstem bronchus is anatomically more vertical, shorter, and wider than the left, so the tube tip more commonly enters it. When the tube rests in the right mainstem bronchus, ventilation goes mainly to the right lung while the left lung receives little to no air, risking hypoxia and unequal chest expansion. The left mainstem bronchus is less likely due to its steeper angle from the trachea, and the tube would not rest in lung parenchyma. The carina is the bifurcation point; the tube should be above it to avoid mainstem intubation. So the over-advanced tube most likely rests in the right mainstem bronchus.