## Cricoid Pressure vs Positive Pressure Ventilation in RSI **Key Point:** Cricoid pressure (Sellick maneuver) and positive pressure ventilation serve complementary but distinct roles in RSI. Cricoid pressure prevents passive regurgitation; positive pressure ventilation maintains oxygenation but may increase gastric insufflation. ### Mechanism of Action | Aspect | Cricoid Pressure | Positive Pressure Ventilation | |--------|------------------|-------------------------------| | **Mechanism** | Compresses esophagus against C6 vertebra | Delivers oxygen-enriched gas to lungs | | **Prevents** | Passive gastric reflux/regurgitation | Hypoxemia during apnea | | **Risk** | Difficult intubation if excessive force | Gastric insufflation → increased aspiration risk | | **Timing** | Applied before induction; maintained until tube confirmed | Applied after loss of consciousness (if needed) | | **Force** | 10 N (1 kg) before LOC; 30 N (3 kg) after LOC | Typically 15–20 cm H₂O | | **Efficacy** | Reduces aspiration risk by ~50% (controversial) | Maintains PaO₂ but may worsen gastric distension | **High-Yield:** The fundamental distinction is **mechanism**: cricoid pressure is a **mechanical barrier** to reflux; positive pressure ventilation is an **oxygenation strategy**. In a full stomach, both are used together—cricoid pressure to prevent regurgitation, and gentle positive pressure (if needed) to maintain SpO₂ without excessive gastric insufflation. **Clinical Pearl:** Modern RSI practice emphasizes **gentle positive pressure ventilation with cricoid pressure** rather than avoiding positive pressure altogether. The goal is to maintain SpO₂ > 90% while minimizing gastric insufflation. **Warning:** Excessive cricoid pressure (>30 N) can compress the trachea, making intubation difficult. Cricoid pressure is NOT a substitute for proper airway assessment and preparation. ## Application in Emergency Cesarean Section 1. **Pre-oxygenation:** 3–5 minutes of 100% O₂ (or 8 vital capacity breaths). 2. **Induction:** IV induction agent (thiopental 5 mg/kg or propofol 2 mg/kg). 3. **Cricoid pressure:** Applied immediately after loss of consciousness (10 N before LOC is controversial; 30 N after LOC is standard). 4. **Gentle positive pressure:** If SpO₂ drops, apply low-pressure ventilation (15 cm H₂O) with cricoid pressure in place. 5. **Intubation:** Confirm tube position; release cricoid pressure only after cuff inflation and tube confirmation. **Mnemonic:** **CRASH** = **C**ricoid pressure prevents **R**egurgitation; **A**ssist with **S**oft **H**and ventilation (gentle positive pressure).
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