Pneumothorax and tension pneumothorax

Why examiners ask this

Pneumothorax is the injected complication in trauma, central line, brachial plexus block, laparoscopy and COPD stems. The examiner wants me to recognize it under positive pressure, where the signs differ from the awake patient, and to act before a radiograph. It stresses adaptability and judgment about when to decompress on clinical grounds alone.

The 60-second answer

Decision points and the "why"

• Clinical diagnosis when unstable — positive pressure turns a small pneumothorax into a tension pneumothorax within minutes, and hypotension from obstructed venous return kills before imaging.
• Decompression site — ATLS now favors the fourth or fifth space at the anterior to mid-axillary line in adults because the chest wall is thinner there and an 8 cm catheter reaches the pleura more reliably; the second space at the midclavicular line remains acceptable, especially in children.
• Chest tube follows — a needle converts tension to simple pneumothorax but does not drain it; I need a definitive tube because positive pressure continues.
• Stop nitrous oxide — it diffuses into the air space 34 times faster than nitrogen leaves and doubles a pneumothorax in about 10 minutes at 70%.
• Ultrasound — absent sliding and absent B-lines suggest pneumothorax; a lung point confirms it; sliding present at the anterior chest excludes it at that point. It is faster and more sensitive than a supine radiograph.
• Small, stable pneumothorax — in a spontaneously breathing patient I observe with oxygen; before positive pressure ventilation, such as an emergency general anesthetic in trauma, I ask for a chest tube first.
• Recognize the setting — I raise my suspicion after a subclavian or internal jugular attempt, a supraclavicular or paravertebral block, rib fractures, bullous disease, high-pressure ventilation and surgery near the diaphragm, such as nephrectomy or upper abdominal laparoscopy; the stem usually plants one of these.
• Capnothorax in laparoscopy — CO2 tracking through a diaphragmatic defect causes high airway pressure and rising end-tidal CO2; it often resolves with desufflation and PEEP because CO2 absorbs quickly, and only needs drainage if it causes instability.

The complication they will inject

A trauma patient with rib fractures is intubated and, after the first few breaths, the pressure falls to 60/40 with an SpO2 of 82%. I recognize tension pneumothorax from positive pressure. I tell the team, decompress the affected side with a needle at the fourth or fifth intercostal space, hear the rush of air, and ask for a chest tube. If the pressure does not recover, I decompress the other side, consider a misplaced or kinked catheter, and look for tamponade and hemorrhage with ultrasound. After the tube, I reassess for an ongoing air leak: a large, persistent leak suggests a bronchial injury, which needs bronchoscopy and lung isolation.

Pitfalls that cost points

• Waiting for a chest radiograph in an unstable patient.
• Stopping at needle decompression without a chest tube.
• Continuing nitrous oxide.
• Forgetting bilateral pneumothorax after bilateral line attempts or blocks.
• Inducing a trauma patient with a known pneumothorax without a chest tube.

Rapid-why

Q: Why is the supine chest radiograph insensitive? A: Air collects anteriorly and medially, so the classic apical edge is absent; the deep sulcus sign is subtle.

Q: Why does a tension pneumothorax cause hypotension? A: Rising pleural pressure compresses the vena cava and the heart, reducing venous return, and shifts the mediastinum.

Q: Which blocks risk pneumothorax? A: Supraclavicular, infraclavicular, intercostal and paravertebral blocks; ultrasound reduces but does not eliminate the risk.

Q: What does M-mode show in a pneumothorax? A: A barcode or stratosphere sign, parallel lines throughout, instead of the seashore pattern of sliding lung.

Numbers to know

Links

• Central venous access and its complications, laparoscopy, Trauma: initial management and damage control, Interscalene block and its complications, Intraoperative hypotension: differential and management
• Atlas: Lung ultrasound: pleura, A/B-lines, effusion, pneumothorax; Monitor atlas: perioperative respiratory events
• ACS Advanced Trauma Life Support (ATLS), 10th edition