3.2 Rapid Sequence Induction (RSI) - Pretreatment & Induction Agents

Rapid Sequence Induction (RSI) — Pretreatment & Induction Agents

Rapid Sequence Induction (RSI) is the administration of a potent induction agent followed immediately by a rapid-acting neuromuscular blocking agent to induce unconsciousness and flaccid paralysis. This technique facilitates emergency endotracheal intubation while minimizing the risk of gastric aspiration in unfasted critical care patients. In transport medicine, selecting the correct pharmacological regimen requires balancing neurological goals against hemodynamic stability.

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1. The 7 Ps of Rapid Sequence Induction

RSI follows a rigorous, chronological execution model known as the 7 Ps:

1. Preparation ($T - 10\text{ min}$): Assemble all primary and rescue airway equipment, suction, monitoring, and vascular access. Conduct the SOAP ME operational checklist (Suction, Oxygen, Airway equipment, Pharmacology, Monitors/ETCO2, Erythrocyte/Emergency plans).
2. Preoxygenation ($T - 5\text{ min}$): Replace nitrogen in the functional residual capacity (FRC) with 100% oxygen using a non-rebreather mask at 15+ L/min or non-invasive positive pressure ventilation (NIV/BiPAP) for 3 minutes, or 8 deep vital-capacity breaths. Apply passive apneic oxygenation via high-flow nasal cannula at 15 to 150 L/min (NO DESAT protocol).
3. Pretreatment ($T - 3\text{ min}$): Administer adjunctive agents to mitigate the physiological complications of laryngoscopy (sympathetic surge, ICP spikes, bronchospasm, or bradycardia).
4. Paralysis with Induction ($T - 0\text{ sec}$): Administer the selected rapid-acting induction agent by rapid IV push, followed immediately by the neuromuscular blocking agent.
5. Protection & Positioning ($T + 30\text{ sec}$): Maintain passive apneic oxygenation. Position the patient in the ear-to-sternal notch alignment (ramped position for obese patients). Avoid routine BVM ventilation to prevent gastric distension unless severe desaturation occurs.
6. Placement with Proof ($T + 45\text{ to } 60\text{ sec}$): Perform direct or video laryngoscopy, pass the ETT through the vocal cords under direct visualization, inflate the cuff, and confirm placement using continuous quantitative waveform capnography ($ETCO_2$) and bilateral auscultation.
7. Post-Intubation Management ($T + 2\text{ min}$): Secure the tube, establish mechanical ventilation, and initiate continuous IV sedation and analgesia infusions.

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2. Pretreatment Pharmacology

Pretreatment agents are given 3 minutes prior to induction to blunt adverse physiological reflexes triggered by laryngoscopy:

Fentanyl

• Dose: $3\text{ mcg/kg IV}$ slowly over 30 to 60 seconds.
• Mechanism: Synthetic opioid agonist acting on $\mu$-receptors; blunts the sympathetic surge (hypertension and tachycardia) caused by laryngeal manipulation.
• Indications: Suspected intracranial hemorrhage, Traumatic Brain Injury (TBI) with elevated ICP, acute aortic dissection, or severe coronary artery disease.
• Contraindications & Pearls: Avoid as a monotherapy in decompensated shock or severe hypotension, as it reduces compensatory sympathetic tone.

Lidocaine

• Dose: $1.5\text{ mg/kg IV}$.
• Mechanism: Class IB antiarrhythmic and local anesthetic; blunts airway cough reflexes, mitigates reflex bronchospasm, and attenuates spikes in ICP during airway manipulation.
• Indications: Severe reactive airway disease (status asthmaticus, COPD exacerbation) and traumatic brain injury with signs of elevated ICP.

Atropine

• Dose: $0.02\text{ mg/kg IV}$ (minimum dose $0.1\text{ mg}$, maximum single dose $0.5\text{ mg}$ in pediatrics).
• Mechanism: Competitive muscarinic acetylcholine receptor antagonist.
• Indications: Prevention of reflex vagal bradycardia in pediatric patients ($< 1\text{ year}$ old) undergoing intubation, or pediatrics receiving succinylcholine (or adult repeated succinylcholine dosing).

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3. Induction Agents Pharmacology

Induction agents produce rapid loss of consciousness. The choice of agent depends primarily on the patient’s hemodynamic status, neurological state, and respiratory pathology.

Etomidate (Amidate)

• Class: Imidazole derivative / non-barbiturate hypnotic.
• Induction Dose: $0.3\text{ mg/kg IV}$ (range $0.2 - 0.4\text{ mg/kg}$). Total dose usually 20–30 mg IV push.
• Onset & Duration: Onset $< 15-30\text{ seconds}$; Duration $5-10\text{ minutes}$.
• Hemodynamic Impact: Hemodynamically neutral. Preserves Systemic Vascular Resistance (SVR), Mean Arterial Pressure (MAP), and Cardiac Output (CO). Does not cause histamine release.
• Neurological Impact: Decreases Cerebral Blood Flow (CBF), Cerebral Metabolic Rate of Oxygen consumption ($CMRO_2$), and Intracranial Pressure (ICP) while preserving Cerebral Perfusion Pressure (CPP).
• Key Adverse Effect: Transient inhibition of $11\beta$-hydroxylase, suppressing adrenal steroidogenesis for 12 to 24 hours. While clinically controversial in sepsis, etomidate remains widely used for single-dose emergency induction in hemodynamically unstable patients.

Ketamine (Ketalar)

• Class: Phencyclidine (PCP) derivative / Dissociative anesthetic.
• Induction Dose: $1.5 - 2.0\text{ mg/kg IV}$ ($4.0 - 5.0\text{ mg/kg IM}$ if vascular access absent).
• Onset & Duration: Onset $30-60\text{ seconds}$ IV; Duration $10-20\text{ minutes}$.
• Hemodynamic Impact: Sympathomimetic. Inhibits central and peripheral catecholamine reuptake, causing increases in heart rate, blood pressure, SVR, and cardiac output. Highly advantageous in shock states.
• Respiratory Impact: Direct smooth muscle relaxant causing potent bronchodilation. Preserves functional residual capacity and intercostal/diaphragmatic respiratory drive.
• Indications: Severe status asthmaticus, septic shock, trauma with hemorrhagic shock, and undifferentiated hypotension.
• Contraindications & Pearls: Relative contraindication in severe ischemic heart disease or active myocardial infarction, as increased myocardial oxygen demand can worsen ischemia. Historical concerns regarding elevated ICP have been disproven in ventilated, normocarbic head trauma patients.

Propofol (Diprivan)

• Class: Alkylphenol derivative / sedative-hypnotic.
• Induction Dose: $1.5 - 2.5\text{ mg/kg IV}$ (reduced to $0.5 - 1.0\text{ mg/kg}$ in elderly or hemodynamically fragile patients).
• Onset & Duration: Onset $15-30\text{ seconds}$; Duration $5-10\text{ minutes}$.
• Hemodynamic Impact: Profound Vasodilator & Myocardial Depressant. Causes significant drops in SVR, preload, stroke volume, and MAP due to direct vascular smooth muscle relaxation and blunting of baroreceptor reflexes.
• Neurological Impact: Potent cerebral protectant; markedly decreases $CMRO_2$, CBF, and ICP. Anticonvulsant properties.
• Indications: Status epilepticus, severe hypertensive head injury with normal perfusion, or hyperdynamic intubations.
• Contraindications: Absolute contraindication in shock, severe hypotension ($SBP < 90\text{ mmHg}$), or hypovolemia.

Midazolam (Versed)

• Class: Benzodiazepine.
• Induction Dose: $0.2 - 0.3\text{ mg/kg IV}$ (Note: This is significantly higher than procedural sedation dosing of $0.05\text{ mg/kg}$). Total dose typically 10–20 mg IV push.
• Onset & Duration: Onset $60-180\text{ seconds}$ (slowest onset of all induction agents); Duration $15-30\text{ minutes}$.
• Hemodynamic Impact: Moderate vasodilator and direct myocardial depressant; causes unpredictable hypotension when combined with opioids.
• Clinical Status: Suboptimal primary induction agent for RSI due to delayed onset and high risk of cardiovascular collapse at full induction doses. Reserved for situations where etomidate, ketamine, and propofol are unavailable.

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Induction Pharmacology Matrix