Preoxygenation Techniques

Preoxygenation Techniques - Oxygen Upfront

• Aim: Maximize body's oxygen stores, primarily within the Functional Residual Capacity (FRC), to prolong time to desaturation during apnea.
• Physiology: Denitrogenation - washing out nitrogen from lungs with 100% oxygen ($FiO_2 = 1.0$).
• Endpoint: Achieve End-tidal Oxygen concentration (EtO₂) > 90%.
• Standard Techniques:
  • 3-5 minutes of tidal volume breathing of 100% O₂ via a tight-fitting mask.
  • 4-8 vital capacity breaths (VCB) of 100% O₂ over 30-60 seconds.
• Key for success: Adequate mask seal, patent airway, patient cooperation.

⭐ Effective preoxygenation can extend the safe apnea time from approximately 1 minute to 5-8 minutes (or more) in a healthy adult by significantly increasing oxygen stored in the FRC.

Preoxygenation Techniques - Breathe Easy Methods

• Goal: ↑ Functional Residual Capacity (FRC) O₂ reservoir; denitrogenation. Extends time to desaturation during apnea.
• Methods:
  • Tidal Volume Breathing (TVB):
    • 100% O₂ via tight-fitting mask.
    • Duration: 3-5 minutes.
    • Most common & effective for routine cases.
  • Vital Capacity Breaths (VCB):
    • 4-8 deep breaths of 100% O₂ over 30-60 seconds.
    • Useful in rapid sequence intubation (RSI) or when time is limited.
• Devices: Face mask with good seal, anesthesia circuit.
• Monitoring: End-tidal O₂ concentration (EtO₂) > 90% indicates adequate preoxygenation.

⭐ During adequate preoxygenation, the primary gas washed out from the lungs is Nitrogen (approx. 79% of FRC initially).

Preoxygenation Techniques - Success Signals

• Monitoring:
  • End-tidal O2 (EtO2): Gold standard. Aim > 90%.
  • Pulse Oximetry (SpO2): Indirect, delayed. Maintain 100%.
  • End-tidal N2 (EtN2): Target < 5%.
• Endpoints:
  • EtO2 > 90% (or > 85%).
  • EtO2 plateau.
  • Time: 3-5 min tidal breathing or 4-8 vital capacity breaths (30-60s).
• Factors Influencing Efficacy:
  • Mask seal integrity.
  • Airway patency.
  • Fresh gas flow (FGF > 5 L/min).
  • Patient FRC & O2 consumption.
  • Pulmonary shunt.

⭐ EtO2 > 90% is the most reliable indicator of successful preoxygenation, reflecting adequate denitrogenation of the FRC.

Preoxygenation Techniques - Tricky Breathers

• Obese Patients (BMI >30-35 kg/m²)

  • ↓FRC, ↑O2 consumption → rapid desaturation.
  • Position: Ramp/HELP (Head Elevated Laryngoscopy Position).
  • CPAP (5-10 cmH2O) beneficial.
  • Target: 3-5 mins or ETO2 >90%.

• Pediatric Patients

  • ↑Metabolic rate, ↓FRC → rapid desaturation.
  • Ensure tight mask seal; cooperation key.

• Pregnant Patients (At Term)

  • ↓FRC (by ~20%), ↑O2 consumption (by ~20%).
  • Left Uterine Displacement (LUD) for aortocaval relief; head-up. 📌

• Critically Ill Patients

  • Underlying lung pathology/shunt common.
  • NIV for preoxygenation if possible.
  • Apneic oxygenation crucial; consider DSI.

⭐ Ramp position (external auditory meatus aligned with sternal notch) in obese patients improves laryngoscopy and safe apnea time.

High‑Yield Points - ⚡ Biggest Takeaways

• Primary goal: Maximize O₂ reservoir (FRC denitrogenation) to ↑ safe apnea time.
• Standard method: 3-5 minutes of 100% O₂ via tight-fitting mask, tidal breathing.
• Rapid alternative: 4 vital capacity breaths of 100% O₂ over 30-60 seconds.
• Effectiveness endpoint: End-tidal O₂ (EtO₂) >90% is the target.
• Apneic oxygenation (e.g., nasal cannula) during laryngoscopy prolongs safe apnea time.
• Crucial in obese, pregnant, pediatric, critically ill (↓FRC, ↑O₂ consumption).