Lateral border of pectoralis major, anterior border of latissimus dorsi, and a line above the fifth intercostal space
Mnemonic
The triangle of safety, bounded by:
- Anterior - the lateral border of pectoralis major
- Posterior - the lateral border of latissimus dorsi
- Inferior - a horizontal line at the level of the nipple, roughly the fifth intercostal space
- Apex - the axilla
Insert just above the rib below, never below the rib above, because the intercostal neurovascular bundle runs in the subcostal groove in the order VAN: Vein, Artery, Nerve, from superior to inferior.
Going too low risks the liver on the right and the spleen on the left; going too posteriorly is painful and kinks the tube.
Expansion
The triangle is bounded by:
- Anteriorly - the lateral border of pectoralis major
- Posteriorly - the anterior border of latissimus dorsi
- Inferiorly - a horizontal line at the level of the nipple, roughly the fifth intercostal space
- Apex - the axilla
Staying inside this triangle keeps the drain above the diaphragm and away from the internal thoracic vessels, the long thoracic nerve and the axillary contents. Combine it with the rule of passing the drain immediately above a rib, since the intercostal vein, artery and nerve run in the costal groove on the underside of the rib above.