110. Hypoxia and Oxygen Therapy – Quiz

📌 Professor’s Notes: Quick Revision

High-yield revision notes for rapid review before university examinations.

• Hypoxia is defined as inadequate oxygen availability at the tissue level. It occurs when oxygen delivery is insufficient or when tissues cannot utilize the available oxygen. Mild physiological hypoxia stimulates erythropoietin production, whereas severe hypoxia causes organ dysfunction.
• Types of hypoxia:
  • Hypoxic hypoxia: Reduced arterial oxygen tension (PaO₂) due to high altitude, hypoventilation, diffusion defects, or ventilation-perfusion mismatch.
  • Anemic hypoxia: Normal PaO₂ but reduced oxygen-carrying capacity due to anemia, carbon monoxide poisoning, or methemoglobinemia.
  • Stagnant (circulatory) hypoxia: Normal oxygen content but inadequate tissue perfusion due to heart failure, shock, or vascular obstruction.
  • Histotoxic hypoxia: Oxygen delivery is normal, but cells cannot utilize oxygen because of toxins such as cyanide, which inhibits cellular respiration.
• Mechanisms of hypoxia:
  • Hypoxic hypoxia results from decreased alveolar oxygen tension or impaired pulmonary gas exchange.
  • In anemic hypoxia, reduced functional hemoglobin limits oxygen transport. Carbon monoxide binds hemoglobin with 200–250 times greater affinity than oxygen and shifts the oxygen-hemoglobin dissociation curve to the left.
  • Stagnant hypoxia causes tissue ischemia, anaerobic metabolism, lactic acidosis, and cellular injury.
  • Histotoxic hypoxia prevents oxidative phosphorylation despite adequate oxygen supply.
• Effects of hypoxia:
  • The brain is the most sensitive organ. Early features include impaired judgment, headache, drowsiness, confusion, and poor coordination. Severe hypoxia may cause loss of consciousness within 15 seconds and irreversible brain damage within 4–5 minutes.
  • Cellular hypoxia activates hypoxia-inducible factors (HIFs), increasing erythropoietin production, angiogenesis, and adaptive responses.
  • Chronic hypoxia causes polycythemia and local vasodilation to improve oxygen delivery.
• Oxygen therapy is indicated in patients with hypoxia, especially those with severe hypoxemia or respiratory distress. Methods include nasal cannula, oxygen mask, oxygen tent, mechanical ventilation, and hyperbaric oxygen therapy.
• Physiological basis of oxygen therapy:
  • Most effective in hypoxic hypoxia, where it increases alveolar and arterial oxygen tension.
  • Provides limited benefit in anemic hypoxia, although hyperbaric oxygen is highly effective in carbon monoxide poisoning by increasing dissolved oxygen and accelerating carbon monoxide removal.
  • Has little benefit in stagnant hypoxia, where restoration of blood flow is essential.
  • Is generally ineffective in histotoxic hypoxia because tissues cannot utilize oxygen, though hyperbaric oxygen may help in selected cases.
• Hyperbaric oxygen therapy involves administration of 100% oxygen at pressures greater than atmospheric pressure. It markedly increases dissolved oxygen in plasma and is mainly indicated for carbon monoxide poisoning and selected cases of severe tissue hypoxia.
• Complications of prolonged 100% oxygen therapy:
  • Central nervous system: Nausea, dizziness, irritability, seizures, and coma.
  • Respiratory system: Airway irritation, decreased surfactant production, atelectasis, pulmonary edema, and inflammation.
  • Eyes: Retinopathy of prematurity in neonates and visual disturbances.