Choosing an induction agent
Stem
A 74-year-old man, 76 kg, with severe aortic stenosis and a preserved ejection fraction, presents for urgent laparoscopic cholecystectomy for acute cholecystitis. He has been vomiting for two days. His blood pressure is 108/64, heart rate 92, and he has no IV access beyond an 18-gauge cannula. The surgeon wants to start within the hour.
Question
What will you induce him with, at what dose, and why?
Ideal answer
HeadlineSevere stenosis, volume depleted: he cannot tolerate a fall in afterload or a fast heart rate. Arterial line, fluid first, phenylephrine running, then rapid sequence with low-dose etomidate.
- Ask what he cannot tolerate: falling preload and afterload, rising heart rate or intracranial pressure, or adrenal suppression.
- Rapid sequence, because he has been vomiting: etomidate at the low end, about 15 mg (0.2 mg/kg), given slowly.
- Sick heart or empty tank: I reduce the dose. Shock, tamponade, severe stenosis, low ejection fraction: etomidate 0.2–0.3 mg/kg1 or ketamine 1–2 mg/kg, a vasopressor running first.
- Propofol only with reserve: 2–2.5 mg/kg in a healthy adult under 55, 1–1.5 mg/kg if elderly, debilitated or ASA III–IV;2 dose matters more than drug.
Watch for: the arterial pressure for the first five minutes after laryngoscopy.
Breaking down the answer
Almost every stem reaches induction; a rote "propofol 2 mg/kg" in a hypovolemic or preload-dependent patient fails it. It tests matching pharmacology to physiology, and the follow-up tests adaptability.
- Propofol's cost — smooth, blunts airway reflexes, reduces nausea, but vasodilation and myocardial depression drop the pressure 20–30% in a healthy patient. Halved doses go in 20 mg aliquots every 10 seconds,2 because the central compartment is smaller and circulation slower.
- Etomidate's cost — it preserves sympathetic tone and contractility, but inhibits 11-beta-hydroxylase for 6–12 hours after one bolus, detectable in most at 12 hours: one dose, never an infusion.1
- Etomidate in sepsis — its use remains debated without proof of harm;1 I give it if it is the safest option, and treat refractory hypotension with stress-dose hydrocortisone.
- Ketamine's limits — its support is indirect (sympathetic stimulation, catecholamine reuptake inhibition) over a direct myocardial depressant, so a catecholamine-depleted patient (sepsis, end-stage heart failure) can still drop pressure.3 I avoid it in uncontrolled coronary disease and aortic stenosis: tachycardia raises oxygen demand.
- Ketamine and intracranial pressure — the label still reports ICP rises and asks for a monitored setting;3 with controlled ventilation the rise is minimal and cerebral perfusion pressure matters more, so I use it in the hypotensive head-injured trauma patient.
- Co-induction — midazolam and opioids lower the hypnotic dose and blunt laryngoscopy, but in tamponade or severe stenosis a large opioid bolus removes the sympathetic tone that holds the pressure. For bronchospasm, ketamine, a bronchodilator, or propofol.
- Special cases — methohexital for ECT, because it does not raise the seizure threshold as propofol does; sevoflurane, non-pungent, for the child without an IV or the critical airway where I want spontaneous breathing preserved.
Follow-up question
Suppose a colleague has already induced him with 120 mg of propofol. The pressure drops to 65/35 with a heart rate of 95. What do you do?
Follow-up answer
HeadlineVasodilation in a fixed-output lesion, a coronary perfusion emergency; I tell the room.
Phenylephrine 100–200 mcg and an infusion, because pure alpha agonism raises diastolic pressure without raising heart rate. A 250 mL fluid bolus, a lighter anesthetic, and surgery held until the pressure is within 20% of baseline. No response: epinephrine 10–20 mcg, the ECG checked for ST changes, and TEE. Then I say what I would change: an arterial line before induction and etomidate titrated with phenylephrine already running.
Pitfalls that cost points
- Assuming ketamine always raises blood pressure.
- Forgetting that a rapid-sequence induction fixes the dose in advance; titration is limited, so the agent must be chosen carefully.
Rapid-fire
Q: Why does propofol drop the pressure more in the elderly? A: Reduced volume of distribution, slower circulation and stiffer vasculature mean a higher peak concentration and less compensatory vasoconstriction.
Q: Why not etomidate in every sick patient? A: It suppresses cortisol synthesis, gives no bronchodilation, causes myoclonus in about a third of patients,1 adds to PONV, and blunts the response to laryngoscopy less than propofol.
Q: Which agent would you choose for a patient with porphyria? A: Propofol, which the label reports has been used safely in porphyria, or ketamine;2 barbiturates are a classic trigger and etomidate is best avoided.
Q: Why give less propofol in tamponade? A: The patient survives on high sympathetic tone and tachycardia; anything that vasodilates or slows the heart collapses cardiac output.
Numbers to know
| Item | Value |
|---|---|
| Propofol induction | 2–2.5 mg/kg; 1–1.5 mg/kg elderly or ASA III–IV2 |
| Etomidate | 0.2–0.3 mg/kg (label range 0.2–0.6)1 |
| Ketamine IV | 1–2 mg/kg (label 1–4.5 mg/kg)3 |
| Methohexital | 1–1.5 mg/kg |
| Etomidate adrenal suppression | 6–12 h after a single dose, resolved by ~48 h1 |
| Phenylephrine bolus | 50–200 mcg |
Links
- Rapid sequence induction and full stomach, Dexmedetomidine and ketamine, Intraoperative hypotension: differential and management, Aortic stenosis, Cardiac tamponade, including post-cardiac surgery, ect
- Surviving Sepsis Campaign guidelines (2021)
Sources
- 1.Etomidate · StatPearls · statpearls.com
- 2.Diprivan (propofol) injectable emulsion prescribing information · FDA label (via RxList) · rxlist.com
- 3.Ketamine hydrochloride injection prescribing information · FDA label (via Drugs.com) · drugs.com
Facts on this page were checked against these sources on Oct 14, 2026. Guidelines change; confirm doses against current institutional protocols.