Hyperventilation = breathing too fast and/or too deeply → blood CO₂ deficiency → blood pH shifts alkaline (respiratory alkalosis).
Mechanism
Normal breathing rate: 12–16 breaths/min. With stress, anxiety, pain, or unfamiliar altitude it rises unconsciously — blood CO₂ falls below normal. Result:
- Cerebral vasoconstriction (brain vessels narrow) → paradoxically worse oxygen supply.
- Tetany in hands and lips (tingling, cramp).
- Dizziness, visual disturbances, loss of consciousness in severe cases.
Cockpit triggers
| Category | Examples |
|---|---|
| Emotions | Fear, excitement, stress, sudden startle |
| Sudden stressful situation | Radio failure, weather surprise, emergency |
| Fear of flying | Especially in students, first flights in unfamiliar configurations |
| Unfamiliar high-attitude states | Stall training, steep turns, aerobatic exercises |
| Pain | E.g. middle-ear problems on descent |
| Incorrect O₂ mask breathing technique | Wrong breathing on pressure-O₂ mask (breathing too fast / shallow instead of slow-deep) |
Symptoms — overlap with hypoxia
| Symptom | Hyperventilation | Hypoxia |
|---|---|---|
| Dizziness | ✓ | ✓ |
| Tingling hands/lips | typical | rare |
| Tetanic cramps (hands/mouth) | typical | no |
| Tunnel vision / blurred | ✓ | ✓ |
| Loss of consciousness | late | early |
| Cyanosis (blue lips / fingernails) | NO — lips normal pink | YES — typical hypoxia symptom |
| Breathing rate | elevated | elevated |
| Skin colour | normal / pale | bluish |
Important to memorise: cyanosis is NOT a hyperventilation symptom. Blue lips or fingernails indicate hypoxia (or CO poisoning) — not hyperventilation.
Treatment
| Step | Action |
|---|---|
| 1 | Deliberately slow breathing — count aloud or speak normal sentences |
| 2 | Breathe into a bag (paper bag) — re-breathe own CO₂, normalises pH |
| 3 | Calm down — address the stressor |
| 4 | If unclear → treat as hypoxia (descend, O₂) |
Key rule
In cockpit doubt: treat as hypoxia. Wrong treatment of actual hypoxia is fatal; wrong treatment of hyperventilation is merely annoying.