Oxygen Therapy

Oxygen Therapy Basics - Breath of Life

• Definition: Administering oxygen at FiO2 > 21% (room air).
• Primary Goal: Treat or prevent hypoxemia and subsequent tissue hypoxia.
• Core Indications:
  • Acute hypoxemia (e.g., pneumonia, ARDS, PE).
  • Chronic hypoxemia (e.g., severe COPD, ILD).
  • Increased metabolic demand (e.g., sepsis, major trauma).
  • Carbon monoxide poisoning.
• Monitoring: Pulse oximetry (SpO2), Arterial Blood Gas (PaO2, SaO2).

⭐ Goal of O2 therapy is to maintain PaO2 > 60 mmHg or SaO2 > 90% in most acute settings.

Delivery Devices - Mask & Cannula Crew

• Low-Flow Devices: Variable FiO2 (patient-dependent).
  • Nasal Cannula: 1-6 L/min → FiO2 24-44%. Mild hypoxia. 📌 CANnula = CAN eat/talk.
  • Simple Face Mask: 5-10 L/min → FiO2 40-60%. Min 5 L/min (↓CO2 rebreath).
  • Partial Rebreather Mask: 6-10 L/min → FiO2 60-80%. Reservoir bag, no 1-way valve.
  • Non-Rebreather Mask (NRM): 10-15 L/min → FiO2 80-95%. Reservoir bag + 1-way valves. Severe hypoxia.
• High-Flow Devices: Fixed FiO2.
  • Venturi Mask: FiO2 24-60% via color-coded adapters (Venturi principle).

    ⭐ Venturi masks are high-flow devices that deliver a precise and constant FiO2, ideal for COPD patients.

  • High-Flow Nasal Cannula (HFNC): Up to 60 L/min; heated, humidified O2; FiO2 21-100%; PEEP.

Monitoring & Titration - Watching the Sats

• Goal: Maintain target SpO2; use lowest FiO2.
• Tools:
  • Pulse Oximetry (SpO2): Continuous, non-invasive.

    ⭐ Pulse oximetry is unreliable in CO poisoning, methemoglobinemia, severe anemia; ABG is essential.

  • Arterial Blood Gas (ABG): PaO2, PaCO2, pH. Gold standard if SpO2 unreliable or for ventilation assessment.
• Targets (SpO2):
  • General: 94-98%.
  • COPD/Hypercapnia risk: 88-92%.
• Process: Titrate FiO2 per SpO2. Wean gradually when stable.

Oxygen's Dark Side - Too Much of a Good Thing

• COPD & CO2 Narcosis:

  ⭐ In COPD patients with chronic CO2 retention, excessive oxygen can depress the hypoxic ventilatory drive, leading to CO2 narcosis and respiratory acidosis.

• Retinopathy of Prematurity (ROP):
  • Premature infants: high, prolonged O2 → retinal vasoconstriction, abnormal vessel growth (neovascularization), potential detachment.
• Pulmonary Oxygen Toxicity:
  • Prolonged FiO2 > 0.6 (e.g., > 24-48 hrs).
  • Symptoms: substernal pain, cough, dyspnea; can lead to ARDS-like damage.
  • Mechanism: ↑ reactive oxygen species.
• Absorption Atelectasis:
  • High FiO2 washes out alveolar nitrogen (splinting effect lost) → alveolar collapse, V/Q mismatch_._

Special Uses & Targets - O2 for VIPs

• CO Poisoning: 100% O2 (non-rebreather), consider HBO.
• Cluster Headache: High-flow O2 (10-15 L/min).
• Pneumothorax: High FiO2 to ↑ N2 washout.
• Decompression Sickness: HBO.
• Anaerobic Infections (e.g., gas gangrene): HBO.
• Cyanide Poisoning: Adjunct.
• Acute Mountain Sickness: Primary treatment.

⭐ For carbon monoxide poisoning, administer 100% oxygen via a non-rebreather mask; consider hyperbaric oxygen (HBO) for severe cases.

High‑Yield Points - ⚡ Biggest Takeaways

• Key indication: Hypoxemia (PaO2 < 60 mmHg or SaO2 < 90%).
• Venturi masks offer precise FiO2, vital for COPD (target SaO2 88-92%).
• Non-rebreathing masks deliver highest FiO2 (near 100%) for severe cases.
• Oxygen toxicity can cause retinopathy of prematurity and pulmonary damage.
• In COPD, avoid suppressing hypoxic drive to prevent CO2 narcosis.
• Hyperbaric oxygen (HBOT) treats CO poisoning, decompression sickness, and gas gangrene.