Decompression sickness
Decompression sickness: nitrogen bubbles out of body tissues when ambient pressure drops too fast (TC AIM AIR 3.3).
- Ground level: tissues saturated with nitrogen (80 percent of air).
- Rapid ascent lowers pressure: nitrogen bubbles, like opening a bottle of pop.
Symptom by bubble location:
| Where bubbles form | Symptom | Name |
|---|---|---|
| In and around blood vessels, joints, muscles | Pain, cramps | Bends |
| Under skin | Itching, tingling | Creeps |
| Lung | Chest pain, shortness of breath; severe cases can cause loss of consciousness | Chokes |
Risk rises with: high rate of climb, age, obesity, physical activity, low temperature.
Limit: above cabin altitude 20,000 ft ASL (6,100 m), do not fly unless crew and passengers completed specialized high-altitude indoctrination training (TC AIM AIR 3.3).
If DCS occurs:
- Descend immediately to a lower altitude (TC AIM AIR 3.3).
- Oxygen mask on, regulator 100 percent. Begin emergency descent. Land as soon as possible (PHAK ch.17).
- Land and seek medical evaluation even if symptoms disappear in descent. Keep breathing oxygen (PHAK ch.17).
- After landing, see an aviation medical specialist: a physician without aviation medicine experience may not recognize it. Definitive treatment may involve a hyperbaric chamber (PHAK ch.17).
- Delayed signs and symptoms can appear on the ground, whether or not present in flight (PHAK ch.17).
Trap: chest pain aggravated by breathing after a climb is the chokes (DCS), not hypoxia: descend immediately and use 100 percent O2. Oxygen never replaces the descent.
References
- TC AIM AIR 3.3
- PHAK ch.17 (FAA-H-8083-25)