Pneumothorax and tension pneumothorax

Ideal answer

HeadlineTension pneumothorax until proven otherwise after a line attempt in emphysema. It is a clinical diagnosis, so unstable means no waiting for a radiograph.¹

1. Help, 100% oxygen, nitrous oxide off, desufflation, while I listen for unilateral loss of breath sounds and check the tube.
2. The differential as I act: capnothorax, bronchospasm, a kinked or endobronchial tube, and anaphylaxis, because each needs a different fix.
3. Lung ultrasound only if it takes seconds: absent lung sliding and a lung point.¹
4. 14-gauge, 8 cm catheter, fourth or fifth space, just anterior to the mid-axillary line, the ATLS site, or the second space at the midclavicular line.²
5. Finger thoracostomy or chest tube immediately after, because needle decompression often kinks or fails and I am still ventilating with positive pressure;¹ then I reassess and look for a second cause.

Breaking down the answer

• Clinical diagnosis when unstable — positive pressure turns a small pneumothorax into a tension pneumothorax within minutes, and obstructed venous return kills before imaging. Under anesthesia: rising airway pressure, falling SpO2 and tidal volume, then hypotension and tachycardia; tracheal deviation and distended neck veins come late.
• Why that site — ATLS now favors the fourth or fifth space in adults because an 8 cm catheter there reaches the pleura in more than 90%;² the second space remains acceptable, especially in children.
• Chest tube follows — a needle converts tension to simple pneumothorax but does not drain it.¹ Changes if: a small, stable pneumothorax breathing spontaneously, which I observe with oxygen; trauma before positive pressure, where I ask for a chest tube first.
• Stop nitrous oxide — it is about 30 times more soluble in blood than nitrogen, so it enters the air space faster than nitrogen can leave;³ in Eger's classic study a pneumothorax doubled in 10 minutes.⁴
• Ultrasound beats the supine film — 94% sensitive and 100% specific in skilled hands.¹ Absent B-lines add to absent sliding; sliding at the anterior chest excludes it at that point.
• Recognize the setting — a subclavian or internal jugular attempt, supraclavicular or paravertebral block, rib fractures, bullous disease, high-pressure ventilation, surgery near the diaphragm such as nephrectomy or upper abdominal laparoscopy; the stem usually plants one.
• Capnothorax in laparoscopy — CO2 through a diaphragmatic defect raises airway pressure and end-tidal CO2; it often resolves with desufflation and PEEP because CO2 absorbs quickly, and needs drainage only if it causes instability.

Follow-up question

Follow-up answer

Pitfalls that cost points

• Forgetting bilateral pneumothorax after bilateral line attempts or blocks.
• Continuing nitrous oxide.

Rapid-fire

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