Induction Agents: Ketamine vs Etomidate
Core Clinical Message
- Neither ketamine nor etomidate is universally hemodynamically stable.
- The induction dose, shock physiology, and preparation for peri-intubation hypotension may matter more than the drug label alone.
Etomidate
Mechanism and Hemodynamic Profile
- Etomidate is a gamma-aminobutyric acid type A (GABA-A) receptor agonist.
- It is generally considered the most cardiovascularly neutral commonly used induction agent.
- Heart rate, blood pressure, and myocardial contractility usually change little after an appropriate induction dose.
- It lowers intracranial pressure and cerebral oxygen demand.
Dose
- Typical induction dose: 0.2 to 0.3 mg/kg intravenously.
Limitations and Adverse Effects
- Etomidate inhibits 11-beta-hydroxylase and can suppress cortisol synthesis for up to 24 hours after a single dose.
- The clinical importance of this effect, particularly in sepsis, remains debated.
- It may cause myoclonus, injection-site pain, and more nausea than some alternatives.
- It does not provide analgesia.
Ketamine
Mechanism and Hemodynamic Profile
- Ketamine is an N-methyl-D-aspartate (NMDA) receptor antagonist and dissociative anesthetic.
- It usually increases heart rate and blood pressure through catecholamine release.
- Ketamine is also a direct myocardial depressant.
- In patients with prolonged shock and depleted catecholamine reserves, direct myocardial depression may predominate and blood pressure can fall after induction.
Clinical Advantages
- Bronchodilation.
- Better preservation of respiratory drive and airway reflexes than many other induction agents.
- Analgesia.
Dose
- Typical induction dose: 1 to 2 mg/kg intravenously.
- Consider a lower dose in shock.
Intracranial Pressure
- The supplied note states that the older concern that ketamine raises intracranial pressure has largely been disproven.
Evidence Summary
- The supplied note describes a 2025 randomized trial of approximately 3,300 critically ill adults.
- It reported no difference in 28-day mortality between ketamine and etomidate.
- Cardiovascular collapse during intubation was reportedly more common with ketamine.
- This source summary does not provide a full citation. Verify the original study before using the result for protocol development or clinical decision-making.
Practical Selection
- Bronchospasm, asthma, or a need for analgesia: ketamine is often a useful option.
- Tenuous hemodynamics or head injury: etomidate is a reasonable option.
- Profound shock: either drug can precipitate collapse.
- Reduce the induction dose.
- Prepare vasopressors and resuscitation measures before induction.
Summary Takeaway
- Neither ketamine nor etomidate is reliably hemodynamically stable in every critically ill patient.
- Select the agent and dose according to the patient's physiology, airway indication, and readiness to treat peri-intubation hypotension.
Follow local protocols and specialist guidance for clinical decisions.
