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

When an endotracheal (ET) tube is advanced too far into the trachea, the most significant indicator is the absence of breath sounds over the left chest. This situation often occurs if the ET tube has gone into the right mainstem bronchus, which means that air is only being delivered to the right lung while the left lung is essentially deprived of ventilation. As a result, breath sounds would be diminished or absent on the left side.

In contrast, absent breath sounds on one side of the chest clearly signal a problem with ventilation. It is crucial for EMTs and other medical professionals to recognize this specific sign to prevent further complications, such as hypoxia or inadequate ventilation to the rest of the body.