42.2 📚 國考版醫垫國考 / PGY OSCE

42.2.0.1 📌 Cram Sheet

42.2.0.1.1 🔥 高 yield 8
  1. Hypoxia 4 類hypoxemic / anemic / circulatory / histotoxic
  2. A-a gradient = (FiO2 × 713 - PaCO2/0.8) - PaO2; normal < 15-20
  3. Hypoventilation = normal A-a, low PaO2; V/Q / shunt / diffusion = high A-a
  4. CO poisoning: SpO2 假高、headache + 玅唇 + 火灜 → 100% O2 / HBO
  5. Methemoglobinemia: chocolate-brown blood, SpO2 ~85% → methylene blue
  6. Cyanide: histotoxic, hydroxocobalamin
  7. Cyanosis = 5 g/dL deoxy Hb absolute
  8. Central = arterial; peripheral = vasoconstriction
42.2.0.1.2 🔢 必背
項目 æ•žå­—
Normal PaO2 80-100 mmHg
A-a gradient normal < 15-20
Cyanosis threshold 5 g/dL deoxy Hb
MetHb cyanosis > 1.5 g/dL (~10%)
SpO2 in MetHb ~85% (regardless actual)
Methylene blue dose 1-2 mg/kg IV
Hydroxocobalamin (cyanide) 5 g IV

42.2.0.2 ⭐ 高 yield

42.2.0.2.1 A-a Gradient Algorithm
  • High A-a + improved with O2 → V/Q mismatch (most)
  • High A-a + 䞍 improved with O2 → shunt
  • High A-a + diffusion → ILD
  • Normal A-a + low PaO2 → hypoventilation or low FiO2
42.2.0.2.2 CO Poisoning
  • Headache, N/V, confusion, seizure, coma
  • Cherry-red skin
  • SpO2 misleadingly normal
  • COHb level
  • 100% O2 → t1/2 from 5h to 90 min
  • HBO for severe (LOC, neuro deficit, pregnancy)
42.2.0.2.3 Methemoglobinemia
  • Drugs: dapsone, benzocaine, nitrate, sulfa, primaquine
  • SpO2 stuck ~85%
  • Chocolate-brown blood
  • Methylene blue 1-2 mg/kg IV (not in G6PD def — use ascorbic acid)
42.2.0.2.4 Cyanide
  • Smoke inhalation, lab, jewelry plating
  • Histotoxic hypoxia
  • Lactic acidosis high
  • Hydroxocobalamin / sodium thiosulfate / nitrites

42.2.0.3 🎯 自我檢枬

  1. CO poisoning SpO2? → Misleadingly normal
  2. MetHb 治療? → Methylene blue (not in G6PD)
  3. A-a gradient normal range? → < 15-20
  4. Hypoventilation A-a? → Normal
  5. Shunt 改善 with O2? → No
  6. Cyanide 解藥? → Hydroxocobalamin
  7. Cyanosis Hb threshold? → 5 g/dL deoxy

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