Hypoxia

Question 1

What is Hypoxia?

Answer 1

Hypoxia = insufficient O₂ to the brain/tissues → degraded night vision, judgment, coordination, and reaction time; can lead to unconsciousness.

Question 2

4 Types (easy memory: the 4 H’s)

Answer 2

• Hypoxic (a.k.a. altitude): Not enough partial pressure of O₂ in the lungs (higher altitude).
• Hypemic: Blood can’t carry O₂ well (e.g., carbon monoxide, anemia, blood loss).
• Stagnant: Blood not moving well (e.g., +G’s, cold-induced vasoconstriction, shock, sitting motionless).
• Histotoxic: Tissues can’t use O₂ (e.g., alcohol, certain drugs/poisons).

Question 3

Common GA Triggers

Answer 3

Altitude (even “moderate” altitudes at night), heater/exhaust CO leaks, smoking, alcohol/sedatives, fatigue/dehydration, cold stress, high workload.

Question 4

Early signs & symptoms (progressive)

Answer 4

• Night vision loss (earliest) → headache, lightheadedness, euphoria, impaired judgment, tunnel vision, cyanosis (blue lips/fingernails), drowsiness, poor coordination, increasing errors, eventually confusion and unconsciousness.
• CO poisoning specifically: dull headache, nausea, “flu-ish,” confusion; pulse oximeter can look normal (it can’t distinguish CO-bound hemoglobin).

Question 5

Time of Useful Consciousness (rule-of-thumb)

Answer 5

• 15,000 ft: ~30+ min
• 18,000 ft: ~20–30 min
• 25,000 ft: ~3–5 min
• 30,000 ft: ~1–2 min
• 35,000 ft: ~30–60 sec
  (Varies with activity, individual, and decompression rate.)

Question 6

Immediate corrective actions (memorize this flow)

Answer 6

1. O₂ ON (100% if available), confirm flow.
2. DESCEND promptly to a lower altitude.
3. MIXTURE RICH, reduce workload.
4. If CO suspected: Cabin heat OFF, open fresh-air vents/windows, use O₂, land as soon as practicable.
5. If severe/rapid onset or a passenger is unresponsive: declare an emergency and get down.

Question 7

Prevention (practical)

Answer 7

• Night flying: use supplemental O₂ above ~5,000 ft MSL to preserve night vision.
• Day: consider O₂ above ~10,000 ft MSL for best performance (earlier if you feel symptoms).
• Install an active CO detector (not just a spot card).
• Avoid alcohol/sedatives; don’t fly when ill or after blood donation; hydrate and rest.
• Smokers already start “behind” (CO in blood), making symptoms appear at lower altitudes.

Question 8

Hypoxia vs. Hyperventilation (they love this comparison)

Answer 8

• Hyperventilation: stress/anxiety → low CO₂, symptoms mimic hypoxia (dizziness, tingling, visual changes).
• Fix: Consciously slow your breathing (talk out loud, count breaths), reduce workload.
  
  • Do NOT “paper-bag” breathe in the cockpit (risk of actual hypoxia).
• If unsure which one it is at altitude, treat as hypoxia first (O₂ + descend) — safest.

Question 9

Checkride talk-track (quick)

Answer 9

• Define hypoxia and list the 4 H’s with one example each.
• Give early symptoms (night vision loss, headache, euphoria) and your immediate actions (O₂—Descend—Rich—Vents/Heat for CO).
• Recite (§ 91.211 Supplemental oxygen) thresholds from memory.
• Add one prevention item (CO detector) and one hyperventilation distinction.