Altitude and a Small Pneumothorax
A 42-year-old man is 36 hours out from a fall onto his right side. He has right-sided rib fractures and a small apical pneumothorax on plain film; there is no hemothorax and he is not hypoxic on the ground (SpO2 96% on room air). He is being transferred by an unpressurized helicopter with a cabin altitude of 8,000 ft (barometric pressure approximately 565 mmHg at sea-level pressure 760 mmHg). He has no chest tube. He is anxious and has pain with deep breathing. The flight is 35 minutes.
1. Using Boyle's law, estimate the change in pneumothorax volume at cabin altitude. What assumptions are you making, and why does this matter clinically?
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Calculation Boyle's law for a fixed amount of gas at constant temperature: P1V1 = P2V2.
- Sea level: P1 = 760 mmHg.
- Cabin altitude 8,000 ft: P2 ≈ 565 mmHg.
- V2 = V1 × (760/565) ≈ 1.35 × V1.
So the trapped gas volume increases by about 35% at 8,000 ft compared with sea level.
Assumptions
- The pneumothorax is a closed space with no gas exchange or leak.
- Temperature remains constant.
- The starting volume is measured at sea-level pressure.
- No supplemental oxygen or nitrogen washout effect is included.
Clinical significance A small pneumothorax can become a tension pneumothorax as gas expands at altitude. Expansion compresses lung, reduces venous return, and worsens hypoxemia. The patient's anxiety and pleuritic pain are early warning signs and should not be attributed only to pain.
2. What are your options to mitigate the risk, and what would you do for this patient?
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Options
- Place a chest tube or pigtail catheter before flight. This is the most reliable way to prevent tension pneumothorax during altitude exposure.
- Fly at a lower cabin altitude or in a pressurized aircraft if a tube cannot be placed.
- Provide supplemental oxygen and continuous monitoring; keep a chest tube kit and needle decompression equipment immediately available.
- Consider ground transport if the risk cannot be mitigated.
- Avoid nitrous oxide, which expands gas spaces.
For this patient He has a known pneumothorax and is about to fly unpressurized. The safest plan is preflight tube thoracostomy or pigtail decompression, even though the pneumothorax is small. If he refuses or the procedure is not feasible, use the lowest possible cabin altitude, give oxygen, monitor closely, and have decompression equipment ready.
Reasoning The decision is not based on the size of the pneumothorax on the ground alone; it is based on the physiologic effect of expansion at altitude. A 35% volume increase in a small space can be tolerated, but the margin is unpredictable, and positive-pressure ventilation or agitation can convert it to a tension physiology.
3. During flight he becomes anxious, then hypotensive (BP 82/50), tachycardic (HR 130), and hypoxic (SpO2 84%). What is happening, and what do you do?
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Interpretation This is tension pneumothorax until proven otherwise. The trapped air has expanded at altitude, compressed the right lung and mediastinum, and impaired venous return. Anxiety, hypotension, tachycardia, and hypoxemia are the classic progression.
Actions
- Perform immediate needle decompression: second intercostal space midclavicular line or fifth intercostal space anterior axillary line on the affected side.
- Follow with tube thoracostomy.
- Give 100% oxygen and support ventilation.
- Descend or pressurize the cabin if possible.
- Treat hypotension with fluid and vasopressor support only after decompression.
Reasoning Positive-pressure ventilation can worsen tension physiology by forcing more gas into the pleural space. Decompression must come first. Needle decompression is a temporizing measure; the chest tube is definitive. Delaying decompression to obtain imaging or to land is dangerous.