Rapid sequence induction

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Rapid Sequence Induction (RSI)

Definition and Purpose

Rapid sequence induction (RSI) - also called rapid-sequence induction and intubation (RSII) - is a specialized technique for IV induction of anesthesia designed to minimize the time between loss of consciousness (LOC) and securing the airway with a cuffed endotracheal tube (ETT). Its primary goal is to prevent pulmonary aspiration of gastric contents in patients at risk for regurgitation.

The core principle: induce unconsciousness and achieve paralysis rapidly, then intubate immediately - without bag-mask ventilation in between - to avoid gastric insufflation and aspiration.

Miller's Anesthesia, 10e
Current Surgical Therapy, 14e

Indications

RSI is indicated when there is an elevated risk of aspiration:

Full stomach (NPO guidelines not observed, emergency surgery)
Bowel obstruction
Trauma (all trauma patients are assumed to have a full stomach)
Morbid obesity
Poorly controlled GERD, diabetic gastroparesis, gastroparesis of any cause
Presence of a nasogastric tube
Pregnancy (classically from 2nd trimester onward, though increasingly questioned)
Predicted difficult mask ventilation (e.g., edentulous/bearded patient) when intubation is expected to be straightforward
Miller's Anesthesia, 10e

The "6 Ps" of RSII (Sequential Steps)

Step	Timing	Key Actions / Agents
Preoxygenation	0-3 min	100% O2 by tight-fitting mask; add nasal cannula at 10-15 L/min for apneic oxygenation
Premedication	3 min	Optional fentanyl, lidocaine, atropine, defasciculating agents (vecuronium/rocuronium at 1/10 induction dose)
Paralysis (induction agent)	3.5-5.5 min	Induction agent (ketamine, etomidate, propofol, midazolam) FOLLOWED BY muscle relaxant
Placement	6-6.5 min	Intubation attempt - no bag-mask ventilation
Performance	7-7.5 min	Confirm ETT position (capnography, auscultation)
Post-intubation management	7.5+ min	Sedation, analgesia, ventilator settings

Current Surgical Therapy, 14e

Preoxygenation

At least 3 minutes of 100% O2 via tight-fitting mask, or 4-8 vital capacity breaths in 60 seconds
Goal: replace alveolar nitrogen with oxygen (denitrogenation), maximizing the apneic oxygenation reserve
In obese, pregnant, pediatric, and critically ill patients, apneic oxygenation time is significantly shorter - supplemental high-flow nasal cannula (up to 60 L/min with HFNC) can extend safe apnea time

Induction Agents

Agent	Dose	Advantages	Disadvantages / Notes
Etomidate	0.2-0.3 mg/kg IV	Hemodynamic stability, rapid onset	Adrenocortical suppression (single dose debatable)
Ketamine	1-2 mg/kg IV	Bronchodilation, maintains airway tone, hemodynamic stability in shock	Increases HR/BP (may be unwanted); dissociative
Propofol	1.5-2 mg/kg IV	Smooth induction, reduces laryngospasm	Hypotension, especially in hypovolemic patients
Thiopental	3-5 mg/kg IV	Classic agent, fast	No longer widely available; causes hypotension
Midazolam	0.1-0.3 mg/kg	Amnestic properties; can be IM	Slower onset (2-3 min); less predictable LOC

Recent evidence update: Multiple 2025 systematic reviews and meta-analyses (PMIDs 39570063, 40239104, 40355221) compared ketamine vs. etomidate for RSI. Overall, both agents show comparable intubating conditions; ketamine may offer advantages in hemodynamically unstable patients, while etomidate remains favored for cardiac stability. Neither agent has shown clear superiority in all contexts - choice should be individualized.

Neuromuscular Blocking Agents

Succinylcholine (depolarizing)

Dose: 1-1.5 mg/kg IV (3-4 mg/kg IM if no IV access)
Onset: ~45-60 seconds; duration 6-10 minutes
Provides optimal intubating conditions fastest
Contraindications: burns (>24-48 h old), crush injuries, immobilization >72 h, upper/lower motor neuron lesions, hyperkalemia, open globe injury, neuromuscular disorders (risk of malignant hyperthermia and hyperkalemic arrest), pseudocholinesterase deficiency

Rocuronium (non-depolarizing, preferred alternative)

Dose: 0.9-1.2 mg/kg IV (standard RSI dose; reversal with sugammadex available)
Onset: 60-90 seconds at high doses
Duration ~45-60 min (much longer than succinylcholine)
Preferred when succinylcholine is contraindicated
Sugammadex (16 mg/kg) can rapidly reverse rocuronium - this has made rocuronium increasingly popular as the primary RSI agent

Vecuronium

0.3 mg/kg IV - used when succinylcholine and rocuronium both unavailable

Cricoid Pressure (Sellick Maneuver)

Applied at the cricoid ring (the only complete cartilaginous ring of the trachea) to compress the upper esophagus and prevent regurgitated gastric contents from reaching the pharynx.

Technique: 10 N of force when the patient is awake, increased to 30 N after LOC
Maintained until ETT cuff is inflated and tube position is confirmed

Controversy:

MRI studies show cricoid pressure causes lateral displacement of the esophagus rather than direct compression - its true mechanism may be occlusion of the hypopharynx
Can decrease lower esophageal sphincter tone (potentially increasing regurgitation risk)
May worsen laryngoscopic view and obstruct the subglottic airway
Excessive pressure during active vomiting has been associated with esophageal rupture
Current consensus: use cricoid pressure unless it impairs laryngoscopy or intubation, in which case it should be released

Miller's Anesthesia, 10e; Morgan & Mikhail's Clinical Anesthesiology, 7e

No Bag-Mask Ventilation ("Hands Off" Rule)

Classically, no positive-pressure ventilation is given between induction and intubation to prevent gastric insufflation. Modifications now accepted:

Gentle mask ventilation (inspiratory pressure <20 cm H2O) while cricoid pressure is maintained is increasingly accepted - particularly in obese, pregnant, pediatric, and critically ill patients where rapid desaturation is a greater risk
Transnasal humidified rapid-insufflation ventilatory exchange (THRIVE) is an emerging modified RSI technique in neonates and infants

Team Requirements

Optimal RSII ideally requires 4 providers:

Intubates and bag-valve-masks if needed
Maintains in-line cervical spine stabilization (trauma)
Applies cricoid pressure
Administers drugs and assists with airway devices

Current Surgical Therapy, 14e

Failed RSI / Cannot Intubate

If intubation fails:

Maintain cricoid pressure; attempt gentle mask ventilation with O2
Retry intubation (video laryngoscopy preferred)
If still unsuccessful, allow spontaneous ventilation to return
Consider awake intubation as the definitive rescue
If rocuronium was used, sugammadex 16 mg/kg IV achieves rapid reversal
If cannot intubate + cannot oxygenate: emergency surgical airway (cricothyroidotomy)

Contraindications / Relative Cautions

RSI is associated with increases in:

Intracranial pressure
Arterial blood pressure
Heart rate

These hemodynamic surges may be problematic in patients with TBI, penetrating eye injury (open globe), or severe hypertension. Pre-treatment with fentanyl (2 mcg/kg) or lidocaine 1.5 mg/kg can blunt these responses.

Pediatric Considerations

Succinylcholine dose: 2 mg/kg in children (higher due to larger volume of distribution)
Succinylcholine should be avoided in patients with known/suspected myopathies - risk of hyperkalemic cardiac arrest
Modified RSI (gentle PPV allowed) is often preferred in neonates/infants due to shorter apneic time from lower FRC and higher O2 consumption
Cricoid pressure must be applied carefully - the pediatric cricoid ring is more compressible and excessive force can obstruct the trachea

Barash Clinical Anesthesia, 9e

Standard vs. RSI - Key Differences

Feature	Standard Induction	Rapid Sequence
Preoxygenation	Routine	Mandatory
Induction-to-intubation time	Longer (allow drug time)	Minimized
Bag-mask ventilation	Used	Avoided (or strictly limited)
Cricoid pressure	Not routinely	Applied
Muscle relaxant	Standard doses, titrated	Full RSI dose given immediately
Patient population	Fasted, elective	Full stomach, emergency, aspiration risk

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