Anaes · Airway management
Rapid sequence induction (RSI) and modified RSI — preoxygenation, the cricoid pressure debate, and the modern approach
Also known as Rapid sequence induction · RSI · Rapid sequence intubation · Modified RSI · Sellick manoeuvre · Cricoid pressure · THRIVE · Apnoeic oxygenation · Preoxygenation
Rapid sequence induction (RSI) is the technique devised to secure the airway of a patient at risk of pulmonary aspiration, the single most feared complication of anaesthesia, by minimising the interval between the loss of consciousness and the placement of a cuffed tracheal tube. The framework rests on four ideas: preoxygenation denitrogenates the functional residual capacity and buys a finite, measurable safe apnoea period whose lower limit is now trackable by end-tidal oxygen; an induction agent followed by a rapid-onset neuromuscular blocker produces unconsciousness and a relaxed jaw within 45 to 60 seconds; cricoid pressure (the Sellick manoeuvre) was the classical safeguard against regurgitation but is now an examined controversy — anatomically unreliable, capable of worsening the laryngoscopic view, and increasingly applied selectively or released if it interferes; and the modified RSI, the modern default, layers gentle mask ventilation, apnoeic oxygenation with high-flow nasal cannula (THRIVE), video laryngoscopy, and rocuronium reversible by sugammadex onto the original sequence, extending safe apnoea and rescuing the cannot-intubate-cannot-oxygenate situation. Anchored to the contemporary evidence on end-tidal oxygen optimisation, cervical spine movement under cricoid pressure, succinylcholine versus rocuronium outcomes, the safety of emergency tracheal intubation, prehospital intermittent-bolus maintenance, and physiological difficult-airway management in the emergency department.
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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 is contraindicated in the burns, crush, denervation, and hyperkalaemic patient after 24 to 48 hours, where it triggers life-threatening hyperkalaemia. Rocuronium 1.2 mg per kg is the safe alternative, and it 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; waveform capnography over six breaths is the standard, and cricoid pressure is released only after confirmation.
Meet the patient
A 35-year-old pregnant woman at 38 weeks arrives in the emergency department obtunded after a seizure. She needs intubation — but pregnancy shortens her safe apnoea period to under two minutes, raises her aspiration risk through a progesterone-relaxed sphincter, and narrows her already difficult airway with oedema. The classical RSI says no mask ventilation; she will desaturate before you place the tube.[6]
The modified RSI says preoxygenate to an end-tidal oxygen above 90 percent, start THRIVE, and ventilate gently — because the hypoxaemia the classical rule risks is a greater harm than the theoretical aspiration it prevents. The question every RSI must answer is simple: how do I secure this airway before my patient desaturates, regurgitates, or arrests?[4][6]
References6ShowHide
- [1]Caputo ND, et al. End Tidal O(2): A Promising New Metric for Optimizing Preoxygenation and RSI Safety in the Emergency Department Acad Emerg Med, 2026.PMID 42340046
- [2]Kumar J, et al. Cervical Spine Movements With Single-Handed Versus Bimanual Cricoid Pressure Under Simulated Cervical Immobilization: A Randomized Controlled Trial J Neurosurg Anesthesiol, 2026.PMID 42333579
- [3]O'Connell DH, et al. Outcomes of Succinylcholine and Rocuronium for Rapid Sequence Intubation in the Emergency Department West J Emerg Med, 2026.PMID 42258841
- [4]Freund Y, et al. Improving the safety of emergency tracheal intubation Curr Opin Crit Care, 2026.PMID 42170830
- [5]Sheridan B, et al. Maintenance of prehospital anaesthesia using an intermittent bolus regime in blunt trauma patients with a high GCS and hemodynamic reserve: a retrospective cohort study Scand J Trauma Resusc Emerg Med, 2026.PMID 42351216
- [6]Ghaffar S, et al. Physiological difficult airway management in the emergency department J Pak Med Assoc, 2026.PMID 42363338