A chest tube is placed into the space between your lung and your chest wall, known as the pleural space. The standard insertion site is on the side of your chest, in the area between the fourth and fifth ribs, roughly level with your nipple. This location sits within a zone doctors call the “triangle of safety,” chosen specifically to avoid major blood vessels, nerves, and organs.
The Triangle of Safety
The triangle of safety is the target zone for nearly all chest tube insertions. It’s a wedge-shaped area on the side of your torso defined by three borders: the outer edge of your chest muscle in front, the front edge of the large back muscle behind you, and a horizontal line at nipple level (the fifth intercostal space) along the bottom. The top of the triangle points up toward your armpit.
This zone is preferred because it sits away from the heart, the major blood vessels running near your breastbone, and the diaphragm below. Placing a tube here also avoids the breast tissue and the thick chest muscles on the front of your body, which would make insertion more difficult and recovery more painful. In practice, the tube enters through the skin on your side, passes between two ribs, and sits inside the pleural space where it can drain air, blood, or fluid.
Why the Tube Goes Above the Rib
Each rib has a bundle of nerves, an artery, and a vein running along its lower edge in a groove called the costal groove. To avoid cutting into these structures, the tube is directed just above the upper border of the lower rib in the chosen space. Nicking the artery or vein can cause bleeding, and damaging the nerve causes significant pain.
There is a smaller, collateral nerve branch that runs along the top edge of each rib as well. This means no entry point within the intercostal space is completely free of nerve tissue, but going above the rib reduces the chance of hitting the larger, main nerve and the blood vessels that travel with it.
How Placement Differs by Condition
The triangle of safety is the go-to site regardless of whether the tube is draining air (as in a pneumothorax, or collapsed lung) or fluid and blood (as in a pleural effusion or hemothorax). What changes is the direction the tube is angled once inside. For air, which rises, the tube tip is typically directed upward and toward the front of the chest. For fluid, which pools at the bottom, the tip is angled downward and toward the back.
In a life-threatening emergency like a tension pneumothorax, where trapped air is compressing the heart and lungs, a needle may be inserted before a full chest tube can be placed. Two sites are used for this emergency needle decompression: the second intercostal space at the midclavicular line (roughly two finger-widths below the collarbone, in line with the middle of the collarbone) or the fourth to fifth intercostal space at the midaxillary line (the side of the chest, within the triangle of safety). On the left side, the midaxillary approach at the fifth space carries some risk of cardiac injury, so the upper chest site is generally preferred for left-sided emergencies.
Small-Bore vs. Large-Bore Tubes
Chest tubes come in different sizes, generally split into two categories. Large-bore tubes are 20 French or larger (roughly the diameter of a pencil) and are used when thick fluid, blood, or large volumes of air need to drain quickly. These are inserted through a small incision using blunt dissection, where the doctor makes a cut, separates the tissue layers with a clamp or finger, and guides the tube in manually. You’ll feel pressure during this process, though the area is numbed with local anesthetic first.
Small-bore tubes are 16 French or smaller (closer to the width of a drinking straw) and work well for simpler fluid collections or smaller air leaks. These are often placed using a guidewire technique: a needle punctures into the pleural space, a thin wire threads through the needle, and the tube slides over the wire into position. This approach is less invasive, often guided by ultrasound or CT imaging, and tends to cause less discomfort during and after the procedure. For many pleural effusions, small-bore tubes drain just as effectively as larger ones.
How Correct Placement Is Confirmed
After a chest tube goes in, a chest X-ray is taken to verify its position. The X-ray shows whether the tube tip is sitting in the right part of the pleural space, whether it’s actually draining what it’s supposed to, and whether the insertion caused any complications like the tube ending up in the wrong tissue layer. If the tube is draining air from a pneumothorax, the X-ray also reveals whether the lung has started to re-expand.
Ultrasound increasingly plays a role before and during placement as well. British Thoracic Society guidelines recommend ultrasound to identify the safest entry point, especially for fluid drainage. Imaging lets doctors see exactly where the fluid is sitting, measure how much is accessible, and spot complications like internal walls of scar tissue dividing the fluid into pockets. This has made chest tube placement substantially safer and more precise compared to using landmarks alone.
What You Feel at the Insertion Site
The insertion site is numbed with local anesthetic injected into the skin, the tissue between the ribs, and the lining of the pleural space itself. You’ll typically feel a stinging sensation from the anesthetic, then pressure and tugging as the tube is positioned. Once in place, the tube is stitched to your skin to keep it from shifting and covered with a dressing. The external end connects to a drainage system, usually a collection chamber with a water seal that allows air or fluid out but prevents anything from flowing back in.
Soreness at the insertion site is common, especially with large-bore tubes, and breathing exercises are encouraged to keep the lung expanding properly. The tube stays in place until drainage slows significantly or imaging confirms the underlying problem has resolved, which can range from a day or two for a simple pneumothorax to a week or more for complicated infections.