Rapid sequence induction (RSI) and modified RSI — preoxygenation, the cricoid pressure debate, and the modern approach

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Red flags

• The standard induction dose of propofol or thiopental will cause cardiovascular collapse in the hypovolaemic, septic, or shocked patient. Reduce the dose, or choose ketamine or etomidate, and have a vasopressor drawn up — haemodynamic instability is the most common major peri-intubation adverse event, far exceeding the rate of difficult intubation itself.
• A patient who is rapidly desaturating during the apnoeic period is failing the classical no-mask-ventilation rule. The modified RSI permits gentle mask ventilation; persisting with an unprotected, hypoxaemic airway to honour the classical sequence is the error the modification was designed to correct.
• Cricoid pressure applied too early, too forcefully, or in the wrong place can obstruct the airway, worsen the laryngoscopic view, and provoke vomiting in the semi-conscious patient. If the view is poor, reduce or release cricoid pressure rather than repeating a failing laryngoscopy — modern practice treats it as optional, not obligatory.
• The safe apnoea period is short in the obese, the pregnant, the child, and the critically ill — often under two minutes from full preoxygenation. These patients are the primary indication for modified RSI with apnoeic oxygenation (THRIVE) and gentle mask ventilation.
• Suxamethonium can trigger life-threatening hyperkalaemia for a period after burns, crush injury, or denervation, and in the already hyperkalaemic patient — the exact high-risk window is debated, so rocuronium 1.2 mg per kg is the safe default once the acute presentation has passed. Rocuronium is reversible with sugammadex 16 mg per kg if a cannot-intubate-cannot-oxygenate situation arises.
• Capnography is mandatory for confirmation of tracheal placement. A tube placed in the oesophagus with cricoid pressure held and the patient paralysed is a catastrophe; sustained waveform capnography is the standard, and cricoid pressure is released only after confirmation.