Anaes · Intravenous induction agents

Intravenous induction agents

Also known as IV induction · Propofol · Thiopental · Ketamine · Etomidate · Midazolam

The intravenous induction agents produce rapid unconsciousness with recovery by redistribution, governed above all by the patient's haemodynamic state. Propofol, etomidate, methohexital and thiopental are GABA-A-receptor agonists while ketamine, nitrous oxide and xenon inhibit NMDA receptors (Philip 2025); intravenous agents modulate GABA-A at sites structurally distinct from volatile agents (Krasowski 1998). Propofol's pharmacokinetics support target-controlled infusion including the general-purpose Eleveld model (Sahinovic 2018); post-infusion kinetics follow the context-sensitive half-time, which elimination half-life cannot describe (Hughes 1992). Etomidate, the only imidazole induction drug with the most favourable single-bolus therapeutic index, inhibits adrenal steroid synthesis beyond its hypnotic action (Forman 2011); it raised adrenal insufficiency (RR 1.64) and mortality (RR 1.19, sepsis 1.22, non-sepsis non-significant) in a 21-article systematic review (Albert 2011), while a 6-RCT emergency-intubation analysis found no mortality difference versus ketamine (28.7 versus 29.9 percent) with less hypotension and more adrenal suppression on etomidate (Andriazzi 2026). Propofol infusion syndrome associates with doses above 4 mg per kg per hour beyond 48 hours across 61 recorded patients (Kam 2007; Bray 1999). Ketamine bronchodilates in severe asthma across 20 reports and 244 patients without definitive-trial backing (Goyal 2013); in traumatic brain injury a 15-study analysis found no mortality or ICP-elevation difference with a hypotension-episode association, and no prospective RCT has demonstrated safety (Sciorilli 2026; BIKe protocol; KETA-BID pilot on spreading depolarisation, not ICP). Barbiturate triggering of porphyria via ALA-synthetase induction is classical (Jensen 1995). Remimazolam is ester-hydrolysed to an inactive metabolite and flumazenil-reversible (Hu 2022); etomidate-analogue design now yields ETO-4 with retained activity and reduced adrenal effect (Zhao 2026); post-induction hypotension favoured etomidate over remimazolam in bypass surgery (Min 2025, etomidate 0.3 mg per kg).