What indicates that an endotracheal (ET) tube has been advanced too far into the trachea?

When an endotracheal (ET) tube is advanced too far into the trachea, it can lead to unintended placement, such as entering the right mainstem bronchus. This misplacement often results in absent breath sounds over the left chest because the left lung is not receiving air due to the obstruction. The right mainstem bronchus is more vertically aligned with the trachea, making it easier for the tube to enter this passageway if advanced excessively, thereby neglecting the left lung entirely.

In contrast, the other options point to different issues. A gurgling sound over the epigastric region typically suggests that the ET tube may have entered the esophagus, leading to air entering the stomach. Crackles over the lower lobe of the left lung may indicate fluid or secretions in the lung rather than confirming improper tube placement. Weak breath sounds over the right lung apex could suggest poor ventilation of the right lung due to a variety of causes, but it does not specifically indicate that the tube has advanced too far into the trachea.