3.2 Rapid Sequence Intubation (RSI) and Medication Selection
Key Takeaways
- RSI involves the near-simultaneous administration of an induction sedative and a neuromuscular blocker to rapidly secure the airway while minimizing aspiration risk.
- Etomidate (0.3 mg/kg) is hemodynamically neutral but causes transient adrenal suppression, requiring caution in severe septic shock.
- Ketamine (1-2 mg/kg) is the preferred induction agent in shocked or asthmatic patients due to its sympathomimetic and bronchodilatory properties.
- Succinylcholine (1.5-2.0 mg/kg) is a depolarizing paralytic contraindicated in hyperkalemic states, burns >24 hours, crush injuries, and malignant hyperthermia.
- Rocuronium (1.0-1.2 mg/kg) is a long-acting non-depolarizing paralytic used when succinylcholine is contraindicated, and can be reversed with sugammadex.
Rapid Sequence Intubation (RSI) and Medication Selection
Rapid Sequence Intubation (RSI) is the cornerstone of emergency airway management in critical care transport. The procedure involves the simultaneous administration of a potent sedative-induction agent and a rapid-acting neuromuscular blocking agent (paralytic) to induce immediate unconsciousness and flaccid paralysis. This technique minimizes the risk of gastric regurgitation and aspiration, blunts autonomic reflexes, and provides optimal intubating conditions. In cases of severe hypoxemia where the patient cannot tolerate apnea, clinicians may utilize Delayed Sequence Intubation (DSI), administering sub-dissociative doses of ketamine to facilitate pre-oxygenation before giving the paralytic.
Pretreatment and Co-Induction Agents
Pretreatment is performed 2 to 3 minutes prior to induction to blunt the physiological responses to laryngoscopy (tachycardia, hypertension, and spikes in intracranial pressure):
- Fentanyl: An ultra-short-acting synthetic opioid. Administered at 1 to 3 mcg/kg IV over 60 seconds. Fentanyl blunts the sympathetic surge associated with airway manipulation, making it highly indicated in patients with TBI, elevated ICP, intracranial hemorrhage, or thoracic aortic dissection. Care must be taken as rapid administration can cause chest wall rigidity and transient respiratory depression.
- Lidocaine: Administered at 1 to 1.5 mg/kg IV. Theoretically, lidocaine blunts the airway reflex, reduces bronchospasm in patients with severe asthma or COPD, and attenuates the rise in ICP during laryngoscopy. While its routine use is debated, it remains highly tested on flight certification exams.
- Atropine: Administered at 0.01 to 0.02 mg/kg IV (minimum dose of 0.1 mg to prevent paradoxical bradycardia). Atropine is a parasympatholytic indicated in pediatric patients (under 1 year of age, and under 5 years if receiving succinylcholine) to prevent profound reflex bradycardia triggered by laryngoscopy and the administration of depolarizing paralytics.
Induction Agents
Induction agents must be selected based on the patient's hemodynamic profile, neurological status, and underlying pathology:
- Etomidate: An imidazole-derivative sedative-hypnotic. Dose: 0.3 mg/kg IV. Etomidate is highly favored in CCT because it is hemodynamically neutral, maintaining blood pressure, heart rate, and cerebral perfusion pressure. It has a rapid onset (10–15 seconds) and a duration of 5–15 minutes. However, etomidate causes transient, reversible adrenal suppression by inhibiting the enzyme 11-beta-hydroxylase. While a single dose is safe, clinicians must exercise caution in patients with refractory septic shock, where cortisol production is already compromised.
- Ketamine: A phencyclidine derivative that produces dissociative anesthesia. Dose: 1 to 2 mg/kg IV. Ketamine acts as a direct bronchodilator and stimulates the sympathetic nervous system, causing catecholamine release that increases heart rate and blood pressure. This makes ketamine the induction agent of choice for patients in hemorrhagic shock, septic shock, and status asthmaticus. Caution is warranted in patients with severe coronary artery disease or hypertensive crises due to increased myocardial oxygen demand.
- Propofol: An alkylphenol sedative-hypnotic. Dose: 1 to 2 mg/kg IV. Propofol has an ultra-rapid onset and offset, making it excellent for neuro-checks. However, it causes profound systemic vasodilation and myocardial depression, leading to severe hypotension. Propofol is contraindicated in hemodynamically unstable or shocked patients.
- Midazolam: A benzodiazepine. Dose: 0.1 to 0.3 mg/kg IV. Midazolam has a slower onset (60–90 seconds) and can cause dose-dependent hypotension. It is rarely used as a primary induction agent in modern RSI but is highly useful for post-intubation sedation.
Neuromuscular Blocking Agents (Paralytics)
Paralytics are divided into depolarizing and non-depolarizing agents based on their action at the nicotinic acetylcholine receptor (nAChR) in the neuromuscular junction:
- Succinylcholine: The only depolarizing neuromuscular blocker in clinical use. Dose: 1.5 to 2.0 mg/kg IV/IO. Succinylcholine binds to the nAChR, causing prolonged depolarization of the muscle membrane, which manifests as visible muscle fasciculations. It has a rapid onset (45–60 seconds) and a short duration (6–10 minutes), making it excellent if a difficult airway is suspected.
- Contraindications: Succinylcholine is contraindicated in patients with a history of malignant hyperthermia (treated with dantrolene), and conditions predisposing to severe hyperkalemia. These include: chronic renal failure with suspected or known hyperkalemia, subacute burns (> 24 hours post-injury), crush injuries or denervation injuries (> 24 hours), and progressive neuromuscular diseases (e.g., Duchenne muscular dystrophy). Succinylcholine administration in these patients can cause a catastrophic surge in serum potassium, leading to ventricular fibrillation and cardiac arrest.
- Rocuronium: A non-depolarizing neuromuscular blocker. Dose: 1.0 to 1.2 mg/kg IV/IO. Rocuronium competitively antagonizes acetylcholine at the nAChR without causing depolarization or fasciculations. A dose of 1.2 mg/kg provides intubating conditions in under 60 seconds (comparable to succinylcholine) but has a long duration of action (40–60 minutes). It is the primary alternative when succinylcholine is contraindicated. Its effects can be rapidly reversed using sugammadex (dose: 2 to 16 mg/kg based on the depth of neuromuscular blockade).
- Vecuronium: A non-depolarizing agent. Dose: 0.1 mg/kg IV. Vecuronium has a slower onset (2 to 3 minutes) and a duration of 45 to 60 minutes. Because of its slow onset, it is not recommended as a primary paralytic for RSI but is frequently utilized in CCT for post-intubation paralysis.
Post-Intubation Sedation and Analgesia
Paralytics do not possess analgesic or sedative properties; intubated patients must never be left paralyzed and awake. Immediately following tube placement and confirmation, clinicians must initiate an infusion of sedatives and analgesics.
- Propofol Infusion: Initiated at 5 to 50 mcg/kg/min, titrated for sedation. Provides rapid emergence but carries a risk of hypotension.
- Fentanyl Infusion: Initiated at 1 to 5 mcg/kg/hr, titrated for pain control.
- Midazolam Infusion: Initiated at 0.05 to 0.3 mg/kg/hr, titrated for sedation. Often combined with fentanyl for synergistic effects.
- Ketamine Infusion: Initiated at 0.5 to 2.0 mg/kg/hr, useful for patients with bronchospasm or those requiring hemodynamic support.
A 45-year-old patient who sustained severe thermal burns over 45% of their body surface area 48 hours ago requires urgent intubation for inhalation injury. Which of the following paralytics is strictly contraindicated in this patient?
Which of the following induction agents is most appropriate for a patient in severe hemorrhagic shock following a motor vehicle collision, due to its ability to preserve hemodynamics via sympathetic nervous system stimulation?