Tension pneumothorax is the third leading cause of preventable death on the battlefield. It happens when air enters the pleural space through a chest wound but can't escape. Each breath pumps more air in, collapsing the lung, shifting the mediastinum, and eventually compressing the heart until cardiac output drops to zero.
Needle chest decompression is the field intervention. It's not complicated, but you need to know when to do it, where to put the needle, and what to do when it doesn't work the first time.
When to decompress
Not every chest wound needs a needle. The decision tree starts with the chest seal.
If you have an open chest wound (sucking chest wound), apply a vented chest seal first. The seal allows air to escape on exhalation through its one-way valve while preventing entry on inhalation. Most casualties do fine with just the seal.
The problem starts when air accumulates faster than the valve can release it, or when the seal creates a closed space. Signs of tension pneumothorax developing:
Progressive respiratory distress after chest seal application. Absent breath sounds on the injured side. Jugular venous distension (JVD). Tracheal deviation away from the injured side (this is a late sign, don't wait for it). Hypotension. Cyanosis.
Step one is to burp the seal. Lift one corner, let trapped air escape, reseal. If the casualty improves, the seal was the problem. If no improvement after burping, proceed to needle decompression.
Where to put the needle
Primary site: 2nd intercostal space, midclavicular line. That means below the clavicle, at the midpoint of the clavicle, in the space between the 2nd and 3rd ribs.
Alternate site: 5th intercostal space, anterior axillary line. This is at the level of the nipple, in the front of the armpit.
The critical rule: insert ABOVE the lower rib. The intercostal neurovascular bundle (vein, artery, nerve) runs in the costal groove along the inferior border of each rib. If you go below the rib, you hit the bundle. Go above the rib below your target space.
Equipment
14-gauge catheter-over-needle, minimum 3.25 inches long. Do not use a 1.5-inch catheter. Studies consistently show that the chest wall thickness at the 2nd ICS in the midclavicular line averages 4.5cm in adult males. A 1.5-inch (3.8cm) needle frequently fails to reach the pleural space, especially in muscular or larger patients. The 3.25-inch (8.3cm) catheter reaches the pleural space reliably.
Technique
- Identify your landmark. Palpate the clavicle, find the midpoint, drop straight down to the space between ribs 2 and 3.
- Prep the site if time allows. In a field scenario, don't delay for a perfect sterile setup.
- Insert the needle perpendicular to the chest wall. Not angled. Perpendicular.
- Advance above the 3rd rib until you feel a rush or hiss of air. That confirms you're in the pleural space.
- Remove the needle. Leave the catheter in place.
- Secure the catheter hub with tape.
- Reassess the casualty. Improvement should be rapid.
When it doesn't work
Catheters kink. They clog with blood. They migrate out of position. Tension pneumothorax can recur after successful decompression.
If symptoms return, decompress again. Same site or alternate site. Multiple decompressions in the same casualty are common and expected. Don't hesitate to repeat the procedure.
If repeated decompressions aren't working, the problem might not be a pneumothorax. Consider hemothorax, cardiac tamponade, or other causes of shock.
Training
Needle decompression is a skill that requires practice on trainers to build confidence with the landmarks and the feel of entering the pleural space. We have interactive training at medeor.app covering site selection, anatomy, and clinical decision-making. The anatomical diagrams show the intercostal space, rib relationships, and neurovascular bundle location so you understand why the landmarks matter, not just where they are.