Hyperbaric oxygen therapy

HBOT Physiology - The Pressure Cooker

• Core Principle: Utilizes Henry's Law ($P = k_H \cdot C$), which states that ↑ ambient pressure ↑ the amount of gas dissolved in a liquid. HBOT involves breathing 100% O₂ at pressures >1.4 atmospheres absolute (ATA).
• Primary Effect: Dramatically ↑ dissolved oxygen in plasma (from 0.3 mL/dL to ~6 mL/dL at 3 ATA), independent of hemoglobin saturation.
• Mechanism: Creates a massive oxygen partial pressure gradient between plasma and ischemic tissues, driving O₂ deep into poorly perfused areas.

⭐ At 3 ATA, dissolved plasma oxygen alone can meet resting metabolic demands, a state where life is theoretically sustainable without red blood cells.

HBOT Indications - Green Light Conditions

Key approved uses for Hyperbaric Oxygen Therapy. Remember the mnemonic 📌 "CAN'T HEAL".

• Carbon Monoxide & Cyanide Poisoning
  • Reduces carboxyhemoglobin half-life from ~300 min (room air) to ~20 min.
• Air or Gas Embolism
  • Reduces bubble size and improves oxygenation to ischemic tissues.
• Necrotizing Soft Tissue Infections
  • Halts toxin production (e.g., Clostridium perfringens alpha-toxin).
• Traumatic Ischemias & Crush Injuries
  • Reduces edema and supports marginal tissue viability.
• Healing-Impaired Wounds
  • e.g., Diabetic foot ulcers (Wagner grade ≥3), refractory osteomyelitis.
• Enhanced Radiation Recovery
  • Treats osteoradionecrosis and soft tissue radiation necrosis.
• Acute Thermal Burns
  • For deep partial-thickness or full-thickness burns, often >20% TBSA.
• Late Radiation Injury

⭐ In CO poisoning, HBOT is critical because it displaces CO from mitochondrial cytochrome c oxidase, restoring aerobic metabolism-a mechanism beyond just clearing carboxyhemoglobin.

HBOT Risks - Red Flags & Dangers

• Absolute Contraindication:
  • Untreated pneumothorax → risk of tension pneumothorax.

⭐ Exam Favorite: The only absolute contraindication to HBOT is an untreated pneumothorax. Air trapped in the pleural space will expand upon decompression, leading to a life-threatening tension pneumothorax.

• Major Risks & Complications:
  • ⚠️ Barotrauma: Most common side effect. Affects ears (tympanic membrane rupture), sinuses, and lungs.
  • Oxygen Toxicity:
    • CNS: Seizures (grand mal), visual changes, tinnitus. Risk ↑ with seizures history.
    • Pulmonary: Substernal chest pain, cough, progressing to ARDS-like picture.
  • Ocular Effects: Reversible myopia is common after multiple sessions.

• Relative Contraindications:
  • COPD/Asthma
  • Claustrophobia
  • Recent fever or seizure
  • Chemotherapy agents (e.g., Bleomycin, Doxorubicin)

High‑Yield Points - ⚡ Biggest Takeaways

• Mechanism: Involves breathing 100% oxygen at pressures >1 atmosphere absolute (ATA), significantly increasing dissolved plasma O2.
• Wound Healing: Promotes collagen synthesis, angiogenesis, and fibroblast proliferation, particularly in hypoxic or ischemic wounds.
• Key Indications: Crucial for diabetic foot ulcers, chronic refractory osteomyelitis, radiation injuries, and gas gangrene.
• Antimicrobial Effects: Directly inhibits anaerobic bacteria (like Clostridium perfringens) and enhances leukocyte killing.
• Major Side Effect: The most common adverse effect is barotrauma to the ears, sinuses, and lungs.