329.1 🎓 醫孞生版

329.1.0.1 📌 䞀頁重點

329.1.0.1.1 High Altitude Illness
329.1.0.1.1.1 Definition
  • Altitude > 2500m (8200 ft) → significant hypobaric hypoxia
  • Higher altitudes (> 3500m) more pronounced
  • 1-2 days of acclimatization needed
  • 25-50% AMS at > 3500m
329.1.0.1.1.2 Pathophysiology
  • ↓ Atmospheric pressure → ↓ PaO2 → ↑ ventilation → respiratory alkalosis
  • Renal compensation (HCO3 excretion) over 1-3 days
  • Hypoxic pulmonary vasoconstriction → ↑ pulmonary pressures (HAPE)
  • Cerebral vasodilation + edema (HACE)
329.1.0.1.1.3 Acute Mountain Sickness (AMS)

Clinical Features: - Headache (#1) - Nausea, vomiting - Insomnia - Fatigue - Anorexia - Lightheadedness - Onset 6-24 hours after arrival

Lake Louise Criteria: - Headache + 1 of (GI, fatigue, insomnia, dizziness)

Risk Factors: - Rapid ascent - Higher altitude (> 3000m) - Previous AMS - Younger age - Heavier exertion

Treatment: - Stop ascent + rest - Hydration - Acetazolamide (250 mg BID) — also for prevention (125-250 mg BID starting 24h before ascent) - Ibuprofen for headache - O2 if available - Descend if not improving

329.1.0.1.1.4 High Altitude Pulmonary Edema (HAPE)

Pathophysiology: - Hypoxic pulmonary vasoconstriction - Heterogeneous (some areas overperfused) - Stress failure of pulmonary capillaries - Non-cardiogenic pulmonary edema

Clinical: - Onset 2-4 days after arrival - Progressive dyspnea - Dry cough → frothy pink sputum - Tachycardia, tachypnea - Hypoxia - Crackles

Imaging: - CXR: patchy bilateral infiltrates

Treatment: - Descend immediately (most important) - Supplemental oxygen - Nifedipine (10 mg followed by 20-30 mg extended-release) — pulmonary vasodilator - Sildenafil alternative - Portable hyperbaric chamber (Gamow bag) if descent impossible - Avoid exertion

Prevention: - Gradual ascent - Nifedipine 30 mg ER BID starting before ascent (high-risk individuals)

329.1.0.1.1.5 High Altitude Cerebral Edema (HACE)

Severe Form: - Progression of AMS - Cerebral edema - Altered mental status, ataxia, coma - Life-threatening

Clinical: - Severe headache (refractory) - Confusion, irritability - Truncal ataxia (hallmark) - Drowsiness → coma - Papilledema possible

Treatment: - Descend immediately - Dexamethasone 4-8 mg IV/IM/PO q6h - Supplemental oxygen - Hyperbaric chamber if descent delayed - ICU support

329.1.0.1.1.6 Prevention of Altitude Illness
  • Gradual ascent: 300-500 m/day above 2500m
  • Rest days every 2-3 days
  • Acetazolamide prophylaxis: 125-250 mg BID, 1-2 days before ascent, continue 2-3 days at altitude
  • Dexamethasone for high-risk
  • Hydration + nutrition
329.1.0.1.2 Diving Emergencies
329.1.0.1.2.1 Decompression Sickness (DCS)

Pathophysiology: - Dissolved N2 (from compressed air) bubbles out on rapid ascent - Boyle’s law (gas expansion) - Bubbles in tissue + blood

Types: - Type I (musculoskeletal/cutaneous): joint pain (“bends”), skin marbling - Type II (neurologic/pulmonary): paresthesias, weakness, paralysis, chest pain, hemoptysis, dyspnea

Risk Factors: - Rapid ascent - Repetitive dives - Cold water - Dehydration - PFO (patent foramen ovale — 2-3x risk) - Obesity - Older age

Diagnosis: - Clinical history of diving + symptoms - Onset within 24 hours of dive

Treatment: - 100% O2 immediately - Hyperbaric oxygen therapy (HBOT) — gold standard - Recompression - Supportive

329.1.0.1.2.2 Arterial Gas Embolism (AGE)

Pathophysiology: - Pulmonary barotrauma (alveolar rupture on ascent) - Gas enters arterial system - Cerebral or systemic gas embolism

Clinical: - Within 10-15 minutes of surfacing - Stroke-like (cerebral) - Cardiac (rhythm disturbances) - Hemoptysis

Treatment: - Trendelenburg or supine (avoid sitting/standing — air migration) - 100% O2 - Hyperbaric oxygen ASAP

329.1.0.1.2.3 Pulmonary Barotrauma
  • Breath-holding during ascent → alveolar rupture
  • Mediastinal emphysema
  • Pneumothorax
  • Subcutaneous emphysema
329.1.0.1.2.4 Drowning + Near-Drowning

Pathophysiology: - Aspiration of water → laryngospasm or water in lungs - Hypoxia → cardiac arrest - Salt vs fresh water differences less clinically significant than once thought

Clinical: - Coma, hypoxia - Aspiration pneumonitis - ARDS - Possible C-spine injury

Treatment: - ABC + CPR - Endotracheal intubation - Lung-protective ventilation if ARDS - Steroids generally not beneficial - Antibiotics only if proven infection

329.1.0.1.3 Inhalation Injuries

329.1.1 Smoke Inhalation

Components: - CO (carbon monoxide): tissue hypoxia - Cyanide: from synthetic materials - Thermal injury: upper airway, ARDS - Particulate matter

Clinical: - Singed nasal hair - Carbonaceous sputum - Hoarseness, stridor (airway swelling) - Hypoxia - Cherry-red appearance (CO — late, unreliable) - Confusion (CO + cyanide) - Cardiac arrhythmia

Diagnosis: - Carboxyhemoglobin (CO-Hb) - Cyanide level - ABG (lactic acidosis) - CXR (may be delayed)

Treatment: - 100% O2 (CO half-life 320 min on room air → 60-80 min on 100% O2) - Hyperbaric O2 for severe (CO-Hb > 25%, neuro symptoms, pregnancy, MI) - Hydroxocobalamin for cyanide (Cyanokit) - Sodium thiosulfate + nitrite (alternative cyanide antidote) - Early intubation for upper airway burns - Lung-protective ventilation

329.1.2 Chemical Inhalation

Chlorine: - Pools, industrial - Tracheobronchitis, pulmonary edema - Treatment: supportive, bronchodilators, steroids

Ammonia: - Industrial, refrigeration - Mucosal damage - ARDS possible - Treatment: supportive

Sulfur Dioxide: - Industrial, volcanic - Bronchospasm - Treatment: supportive

Nitrogen Dioxide: - Silo filler’s disease (silage off-gas) - Delayed bronchiolitis obliterans - Treatment: steroids if developing

Phosgene: - WWI chemical weapon, industrial - Delayed pulmonary edema 6-24 hours - Treatment: supportive

Hydrogen Sulfide: - Industrial (oil, gas, sewers) - Olfactory paralysis at high concentrations - Treatment: supportive

329.1.3 Thermal Injury

Upper Airway: - Singed nasal hair, soot, stridor - Early intubation - Tracheal stenosis late

Lower Airway: - Less common (thermal limited to upper) - Steam injury can reach lower

329.1.3.0.1 Other Environmental Pulmonary Disease

329.1.4 Cold-Induced Bronchospasm

  • Cold air → mediator release
  • Asthmatic exacerbation
  • Treatment: pre-exercise SABA + warming inspired air

329.1.5 Hot Weather + Exercise

  • Heat stroke + respiratory failure
  • Often part of MOF
  • Aggressive cooling

329.1.6 Air Pollution Acute Effects (Ch306)

  • Wildfires
  • Smog episodes
  • Stay indoors, masks

329.1.6.1 🩺 床邊速查

  • AMS: HA + GI + fatigue at > 2500m; acetazolamide
  • HAPE: rapid dyspnea, frothy sputum; descend + O2 + nifedipine/sildenafil
  • HACE: AMS + ataxia + altered mental status; descend + dexamethasone
  • DCS: post-dive joint/neuro symptoms; 100% O2 + HBOT
  • AGE: post-dive stroke-like symptoms; Trendelenburg + 100% O2 + HBOT
  • Smoke inhalation: CO + cyanide + thermal; 100% O2 + Cyanokit if cyanide suspected + HBOT for severe CO
  • Phosgene: delayed pulmonary edema 6-24 hr
  • NO2 (silo): delayed bronchiolitis obliterans