Rapid sequence induction details from millers Anaesthesia
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Rapid-Sequence Induction (RSI) — Miller's Anesthesia, 10th Edition
Definition & Goal
Rapid-sequence induction and intubation (RSII — often simply called RSI in the anesthesia literature) is a specialized IV induction technique used when there is an increased risk of gastric regurgitation and pulmonary aspiration. The core goal is to achieve optimal intubating conditions as rapidly as possible, minimizing the time between loss of consciousness (LOC) and securing the airway with a cuffed endotracheal tube (ETT).
— Miller's Anesthesia, 10e, p. 5862
Indications
| Category | Examples |
|---|---|
| Absolute | Full stomach (NPO guidelines not followed), bowel obstruction |
| Strong | Pregnancy (≥2nd trimester — though increasingly debated) |
| Relative | Poorly controlled GERD, nasogastric tube in situ, morbid obesity, diabetic gastroparesis |
| Airway | Difficult mask ventilation predicted but intubation not difficult (e.g., edentulous bearded patient) |
Step-by-Step Technique
1. Preoxygenation (Denitrogenation)
Preoxygenation replaces nitrogen in the lungs with oxygen, extending safe apnea time before oxyhemoglobin desaturation.
- Delivery: 100% O₂ via tight-fitting face mask at 10–12 L/min (to prevent rebreathing); no leaks
- Target: End-tidal O₂ > 90%
- Safe apnea time after maximal preoxygenation:
- Healthy non-obese adult: ~9 minutes to SpO₂ < 80%
- Obese or pediatric patients: ≤ 3 minutes
Methods:
| Method | Protocol | Efficacy |
|---|---|---|
| Tidal volume breathing | 3 minutes of normal breathing | Gold standard — exchanges 95% of lung gas |
| Vital capacity breaths (4) | 4 breaths over 30 seconds | Inferior to tidal method |
| Vital capacity breaths (8) | 8 breaths over 60 seconds | More effective than 4-breath method |
| THRIVE | 60 L/min humidified O₂ for 3 min | Equivalent to tidal method; extends apnea time further |
| End-tidal monitoring | Continue until EtO₂ ≥ 90% | Objective endpoint |
Adjuncts: Head-up positioning improves preoxygenation in both obese and non-obese patients. NIPPV also prolongs apnea time. Apneic oxygenation via nasal cannula at up to 15 L/min (NO DESAT technique) or THRIVE during laryngoscopy further extends safe apnea time.
— Miller's Anesthesia, 10e, pp. 5852–5855
2. IV Induction Agent
Although thiopental was the traditional agent, modern practice uses:
| Agent | Notes |
|---|---|
| Propofol | Commonly used; dose-dependent hypotension |
| Etomidate | Favored in hemodynamic instability; adrenal suppression concern |
| Ketamine | Preferred in bronchospasm, hemodynamic compromise |
| Thiopental | Traditional agent; largely replaced in modern practice |
Some practitioners titrate to LOC rather than deliver a fixed predetermined dose.
3. Neuromuscular Blocking Drug (NMBD)
Administered immediately after (or simultaneously with) the induction agent — no PPV is attempted between induction and intubation.
| Agent | Dose | Time to intubation | Duration |
|---|---|---|---|
| Succinylcholine | 1.0–1.5 mg/kg IV | ~60 seconds | Ultra-short (5–10 min) |
| Rocuronium | 1.0–1.2 mg/kg IV | < 90 seconds | Prolonged (reversal with sugammadex 16 mg/kg) |
| Vecuronium | 0.3 mg/kg IV | < 90 seconds | Prolonged |
Succinylcholine remains the prototypic agent. Rocuronium + sugammadex is an increasingly preferred alternative because sugammadex reversal of high-dose rocuronium is faster than spontaneous recovery from succinylcholine.
4. Cricoid Pressure (Sellick Maneuver)
Applied during the sequence — from awake state through to ETT cuff inflation and confirmation.
- Awake: 10 Newtons
- After LOC: 30 Newtons (based on esophageal manometry and cadaver studies)
- Mechanism: Originally thought to compress the esophagus; MRI studies show it may instead occlude the hypopharynx
Controversies:
- May decrease lower esophageal sphincter tone (potentially worsening aspiration risk)
- MRI shows lateral esophageal displacement rather than occlusion
- Worsens laryngeal view on direct laryngoscopy (DL); can obstruct subglottic airway
- Consensus: Because of its low risk profile, cricoid pressure is still recommended for RSI, but should be released if it impedes laryngoscopy or intubation
5. Intubation
Performed without PPV (avoiding gastric insufflation). Confirm ETT placement before releasing cricoid pressure.
Modified RSI
No standardized definition exists. In US survey data, most commonly refers to mask ventilation + cricoid pressure (gentle PPV, inspiratory pressure < 20 cm H₂O).
Indications for modified RSI:
- Risk of rapid hypoxemia (obesity, pregnancy, critical illness, pediatrics)
- Emergent situations where preoxygenation cannot be completed
- Use of standard-dose nondepolarizing NMBDs (longer onset than succinylcholine/high-dose rocuronium)
— Miller's Anesthesia, 10e, pp. 5863–5864
Classic vs. Modern RSI Summary
| Feature | Classic RSI (1970) | Modern Practice |
|---|---|---|
| Induction agent | Thiopental (fixed dose) | Propofol, etomidate, or ketamine (may titrate to LOC) |
| NMBD | Succinylcholine 1–1.5 mg/kg | Succinylcholine or rocuronium 1.2 mg/kg + sugammadex |
| PPV | None | None (modified RSI allows gentle PPV < 20 cmH₂O with cricoid) |
| Cricoid pressure | Mandatory | Recommended; release if impedes intubation |
| Preoxygenation | Standard face mask | THRIVE, NIPPV, apneic oxygenation adjuncts available |
Contraindications to Succinylcholine (when rocuronium is preferred)
- Hyperkalemia or risk thereof (burns, crush injuries, denervation, prolonged immobility)
- Malignant hyperthermia susceptibility
- Pseudocholinesterase deficiency
- Increased intraocular pressure (relative)
- Myopathies
— Miller's Anesthesia, 2-Volume Set, 10e, pp. 5862–5864
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