302.2 🩺 國考版

302.2.1 高頻考點

302.2.1.1 Hypoxemia Mechanisms

• V/Q mismatch: most common
• Shunt: O2 doesn’t help
• Hypoventilation: normal A-a gradient
• Diffusion impairment: ↓ DLCO
• Low FiO2: altitude

302.2.1.2 A-a Gradient

• Normal: 5-15 (young); age/4 + 4
• ↑ in V/Q, shunt, diffusion
• Normal + hypoxemia = hypoventilation / low FiO2

302.2.1.3 Chronic Cough — Top 3

1. UACS (post-nasal drip)
2. Asthma (cough-variant)
3. GERD

302.2.1.4 Chronic Cough Workup

• 80-90% explained by UACS + asthma + GERD
• Empiric trial often
• Methacholine challenge for cough-variant asthma
• ACE inhibitor culprit (switch to ARB)
• HRCT for structural causes
• Refractory: gefapixant (P2X3) 2024 FDA

302.2.1.5 Hemoptysis

• Trivial < 30 mL/d
• Massive > 200 mL/d
• Common causes: bronchitis, bronchiectasis, lung cancer, TB, PE, AVM
• Workup: CT > CXR
• Massive: ABC, selective intubation, bronchial artery embolization

302.2.1.6 Dyspnea Differential

• Cardiac vs pulmonary vs anemia vs deconditioning vs anxiety
• mMRC scale 0-4
• 6MWT for severity

302.2.1.7 Chronic Hypercapnia

• HCO3 compensation 3.5 mEq/L per 10 mmHg ΔPaCO2
• pH near normal
• Common: severe COPD, OSA, obesity hypoventilation, neuromuscular disease

302.2.2 易混淆比較

Mechanism	A-a Gradient	O2 Response	Examples
V/Q mismatch	↑	+ (improves)	COPD, asthma, pneumonia, PE
Shunt	↑↑	- (no improve)	ARDS, AVM, severe pneumonia
Hypoventilation	Normal	+ (improves)	Drug OD, NM disease, OSA
Diffusion	↑	+ (improves)	ILD, emphysema
Low FiO2	Normal	+ (improves)	Altitude

302.2.3 Special Topics

302.2.3.1 Chronic Cough Algorithm

1. Smoker → stop smoking
2. ACE inhibitor → discontinue
3. CXR + spirometry
4. Empiric UACS treatment (nasal steroid + antihistamine)
5. Asthma trial (ICS / methacholine)
6. GERD trial (PPI + lifestyle)
7. If refractory → HRCT, bronchoscopy, ENT, gefapixant

302.2.3.2 Pulmonary vs Cardiac Dyspnea

• Cardiac: orthopnea, PND, S3, edema
• Pulmonary: cough, wheeze, sputum, position-independent
• BNP often helpful

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