What typically causes right mainstem intubation?

The correct choice is the insertion of the endotracheal (ET) tube too deep, which typically leads to right mainstem intubation. This occurs because the anatomy of the tracheobronchial tree is such that the right main bronchus is wider and more vertically oriented compared to the left. Consequently, if the tube is advanced too far into the trachea, it is more likely to slip into the right mainstem bronchus rather than into the left.

When intubating a patient, the goal is to position the ET tube within the trachea just above the carina, the junction where the trachea divides into the left and right bronchi. Inserting the tube too deeply bypasses this point, leading to ventilation of the right lung only, which can result in inadequate oxygenation of the left lung. This complication is significant because it can lead to problems such as hypoxia and uneven ventilation.

While the angle of insertion, tube size, and visualization can certainly contribute to intubation difficulties, it is the depth of insertion that predominantly influences the risk of mistakenly entering the right mainstem bronchus.