Rapid Sequence Intubation: Securing the Airway in Seconds

What RSI Is and Why It Matters at the Bedside

Rapid sequence intubation is the technique of choice for emergency tracheal intubation in patients who are not fasted — which, in the ED and ICU, means essentially everyone. The premise is simple but powerful: any acutely ill patient may have a full stomach, obtunded protective reflexes, or both, and is therefore at high risk of regurgitation and pulmonary aspiration of gastric contents (Mendelson syndrome, first described in obstetric anesthesia in 1946).

To minimize that risk, RSI deliberately omits the bag-valve-mask ventilation that is standard in an elective anesthetic induction. Positive-pressure ventilation insufflates the stomach, raising intragastric pressure and regurgitation risk. Instead, the patient is preoxygenated to build an oxygen reservoir, then rendered unconscious and paralyzed almost simultaneously, and intubated during the resulting apnea.

• Indications: declining GCS, respiratory failure, airway protection, anticipated clinical course (e.g., severe sepsis, trauma, overdose).
• Goal: first-pass success with the shortest possible interval of unprotected apnea.

The Mechanism: Pharmacology of Induction and Paralysis

RSI works by attacking two targets at once — consciousness and neuromuscular tone — timed so paralysis peaks just as the sedative takes hold.

Induction agents abolish awareness within seconds. Etomidate and propofol are positive allosteric modulators of the GABA-A receptor, enhancing chloride influx and hyperpolarizing neurons; propofol also causes vasodilation. Ketamine instead blocks the NMDA glutamate receptor, producing a dissociative state while stimulating catecholamine release — hence its blood-pressure-sparing, bronchodilating profile.

Neuromuscular blockers paralyze the diaphragm and laryngeal muscles at the motor endplate:

• Succinylcholine is a depolarizing agent — two acetylcholine molecules fused — that binds the nicotinic ACh receptor, opens the channel, and keeps it depolarized, causing transient fasciculations then flaccid paralysis. It is hydrolyzed by plasma pseudocholinesterase, giving its uniquely short duration.
• Rocuronium is a non-depolarizing competitive antagonist at the same receptor — no fasciculations, longer duration, and reversible with sugammadex (which encapsulates the molecule).

The Clinical Sequence: The 7 Ps

RSI is executed as a choreographed sequence, memorized as the 7 Ps, ideally with a shared mental model and a checklist:

• Preparation — SOAP ME: Suction, Oxygen, Airway equipment (blades, tubes, bougie, video laryngoscope), Pharmacy, Monitoring, End-tidal CO2. Assess for a difficult airway (LEMON, MOANS, RODS).
• Preoxygenation — 3 minutes of high-FiO2 or 8 vital-capacity breaths to denitrogenate the lungs and fill the functional residual capacity with oxygen.
• Pretreatment / physiologic optimization — resuscitate before you intubate: correct hypotension (fluids/pressors, push-dose epinephrine), consider the 'resuscitation sequence.'
• Paralysis with induction — push the induction agent, immediately followed by the paralytic.
• Positioning — 'ear-to-sternal-notch' sniffing position; head-up improves preoxygenation and view.
• Placement with proof — laryngoscopy, tube through the cords, confirm.
• Post-intubation management — secure tube, sedate/analgese, lung-protective ventilation, chest X-ray.

Confirmation and Monitoring: Proving the Tube Is in the Trachea

The single most important post-placement step is proof of tracheal placement — because an unrecognized esophageal intubation is rapidly fatal.

• Waveform capnography is the gold standard: a sustained, square-wave end-tidal CO2 tracing over at least 6 breaths confirms the tube is in the trachea. In cardiac arrest with low pulmonary blood flow, EtCO2 may be low, but a persistent waveform still confirms placement.
• Colorimetric CO2 detectors (purple-to-yellow) are a backup but can be misled by antacids or carbonated stomach contents and by low-flow states.
• Direct visualization of the tube passing between the vocal cords, chest rise, bilateral breath sounds, absence of epigastric gurgling, and fogging of the tube are supportive but not definitive.

Continuous pulse oximetry tracks oxygenation trend; a falling SpO2 with a good capnography waveform points to a lung problem (pneumothorax, mainstem intubation, bronchospasm) rather than a misplaced tube. A post-procedure chest radiograph confirms depth (tip ~3-5 cm above the carina) but does not exclude esophageal placement — only capnography does that.

Complications and Physiologic Optimization

Peri-intubation complications are common and can be lethal; the ED airway is a resuscitation, not just a technical procedure.

• Hypoxemia — the most frequent adverse event. Mitigate with thorough preoxygenation and apneic oxygenation (nasal cannula at 15 L/min running through the apneic period, leveraging aventilatory mass flow).
• Hypotension and peri-intubation arrest — driven by loss of sympathetic tone, positive-pressure-induced drop in preload, and the induction agent's vasodilation. The shock index (HR/SBP) > 0.9 predicts collapse. Optimize hemodynamics first; choose ketamine or reduced-dose induction in shock.
• Succinylcholine-specific — hyperkalemia (dangerous in burns/crush >72 h, denervation, rhabdomyolysis, chronic paralysis due to upregulated extrajunctional receptors), malignant hyperthermia (RYR1-mediated, treat with dantrolene), bradycardia (especially in children/repeat dosing), and masseter spasm.
• Aspiration and esophageal intubation — the very events RSI exists to prevent.

Cricoid pressure (Sellick maneuver) is now controversial and often abandoned, as evidence for aspiration prevention is weak and it can worsen the laryngeal view.

Distinctions, Mimics, and Pitfalls

RSI is one of several airway strategies, and choosing correctly is a board-favorite decision point.

• RSI vs. awake intubation: when a difficult airway is anticipated and the patient can cooperate, an awake fiberoptic/video intubation under topical anesthesia preserves spontaneous ventilation and airway reflexes — never paralyze a patient you cannot ventilate or intubate ('can't intubate, can't oxygenate' is the feared endpoint).
• RSI vs. delayed sequence intubation (DSI): in the agitated, desaturating patient who won't tolerate preoxygenation, DSI uses dissociative-dose ketamine first to allow preoxygenation, then paralysis — a 'procedural sedation for preoxygenation.'
• Paralytic pitfalls: giving rocuronium (30-60 min paralysis) then failing to intubate leaves a paralyzed, apneic patient — have a rescue plan (supraglottic airway, cricothyrotomy) and sugammadex available.
• Do-not-miss: forgetting post-intubation sedation paralyzes an awake patient — a catastrophic 'awareness' pitfall when a long-acting paralytic outlasts the induction agent.

RSI induction and paralytic agents — dose, onset, duration, and key clinical considerations

Agent	Class / Dose (IV)	Onset / Duration	Key clinical pearl
Etomidate	Imidazole hypnotic; 0.3 mg/kg	15-45 s / 5-15 min	Hemodynamically neutral; transient adrenal suppression (11-beta-hydroxylase inhibition) — avoid debate in septic shock
Ketamine	NMDA antagonist; 1-2 mg/kg	30-40 s / 10-20 min	Sympathomimetic — preserves BP; bronchodilator; ideal for shock/asthma; 'dissociative' induction
Propofol	GABA-A agonist; 1.5-2.5 mg/kg	15-45 s / 5-10 min	Causes vasodilation/hypotension; reserve for hemodynamically stable, e.g., status epilepticus
Succinylcholine	Depolarizing NMB; 1.5 mg/kg	~45 s / 6-10 min	Fastest offset; contraindicated in hyperkalemia risk (burns/crush >72 h, denervation), malignant hyperthermia
Rocuronium	Non-depolarizing NMB; 1.2 mg/kg	~60 s / 30-60 min	No hyperkalemia/MH risk; long paralysis (can't wake a failed airway); reversible with sugammadex