right main bronchus

**Anatomy** - Arises from the tracheal bifurcation (carina) at the level of the sternal angle (T4–T5). - Length ~2.5 cm (vs ~5 cm on the left). Wider and more vertical (~25° from midline vs ~45° on the left). - Gives off the right upper lobe bronchus (eparterial bronchus) before entering the hilum, then continues as the bronchus intermedius, which divides into the middle and lower lobe bronchi. - Right lung: 3 lobes (upper, middle, lower), 10 bronchopulmonary segments. Left lung: 2 lobes, 8–10 segments (lingula in place of the middle lobe). - The azygos vein arches over the right main bronchus to enter the SVC. The left main bronchus is crossed by the aortic arch and lies anterior to the esophagus and descending aorta. - Relations at the hilum (right): the RALS mnemonic (Right Anterior to Left Superior) describes the pulmonary artery. The right pulmonary artery is anterior to the bronchus. The left pulmonary artery arches over the left main bronchus. The "Eparterial" right upper lobe bronchus lies above the pulmonary artery, and "hyparterial" bronchi lie below it.

**Clinical significance** - **Aspiration:** Because of its wider, more vertical course, aspirated foreign bodies and material usually enter the right main bronchus. - Upright or sitting patient: right lower lobe (basal segments). - Supine patient: right upper lobe (posterior segment) or right lower lobe (superior segment). - Aspiration pneumonia and lung abscess are therefore commonly right-sided. - Foreign body aspiration in children: unilateral wheeze, air trapping, and hyperinflation on expiratory or decubitus films. - **Endotracheal intubation:** A tube advanced too far enters the right main bronchus. This causes right-sided ventilation only, with absent breath sounds and decreased chest expansion on the left, hypoxemia, and possible left lung atelectasis. Confirm placement with chest x-ray (tip ~2–4 cm above the carina). Treat by withdrawing the tube. - **Bronchogenic carcinoma:** Central tumors (squamous cell carcinoma, small cell carcinoma) may involve the main bronchi and cause obstruction, postobstructive pneumonia, or atelectasis. - **Azygos vein relationship:** Mediastinal masses or adenopathy near the carina can compress the main bronchi. Subcarinal lymph nodes can splay the carina.

**High-yield pearls** - Right main bronchus = shorter, wider, more vertical → aspiration and intubation complications. - Carina is at T4–T5 (sternal angle, level of the aortic arch end and tracheal bifurcation). - The right pulmonary artery crosses anterior to the bronchus intermedius, and the left pulmonary artery arches over the left main bronchus.