• Clinical science

Intravenous anesthetics

Summary

Intravenous anesthetics are a group of fast-acting compounds that are used to induce a state of impaired awareness or complete sedation. Commonly used intravenous anesthetics include propofol, etomidate, ketamine, and barbiturates (e.g., thiopental). Propofol is the standard drug for induction of anesthesia and etomidate is most commonly used in cases of hemodynamic instability. Ketamine plays a key role in emergency medicine because of its strong dissociative, sympathomimetic, and analgesic effects. The barbiturate thiopental reduces intracranial pressure, making it useful in patients with high intracranial pressure and/or head trauma. While the characteristics and side effects of intravenous anesthetics are highly dependent on the substance involved, they all share a strong hypnotic effect.

For more information on benzodiazepines and opioids, see the corresponding learning cards.

Overview

Indication Characteristics
Propofol
Etomidate
  • IV anesthesia for patients with hemodynamic instability
  • ↓ Intracranial pressure
  • Little to no effect on the cardiovascular system
Ketamine
  • Ideal emergency anesthesia for polytrauma patients
  • Short painful procedures (e.g., fracture reduction)
  • Treatment-resistant asthma
Barbiturates (thiopental and methohexital)
Opioids (e.g., fentanyl, morphine)
  • Analgesia during induction and/or maintenance anesthesia
  • Muscle rigidity
  • Cardiovascular and respiratory depression
Benzodiazepines (e.g., midazolam)
  • IV anesthesia induction
  • Short outpatient procedures
  • Preoperative sedation
  • Endoscopy

References:[1][2][3]

Propofol

Mechanism of action

  • Not fully understood. Propofol is thought to act at GABAA receptors and sodium channels of the reticular formation.
  • Rapid onset and recovery

Effects

Side effects

Indications

References:[3][4][5][6]

Etomidate

Mechanism of action

  • Acts on the GABA receptors in the reticular formation
  • Rapid onset and recovery

Effects

  • Hypnotic effects
  • ↓ Intracranial pressure
  • Anticonvulsant effects
  • Little to no effect on the cardiovascular system
  • Little to no effect on respiration
  • No analgesic or muscle relaxant effect

Side effects

Indications

  • Anesthesia for patients with hemodynamic instability

Of all the IV anesthetics, etomidate has the least impact on the cardiovascular system!

References:[3]

Ketamine

Mechanism of action

Effects

Side effects

  • Nystagmus
  • ↑ Oxygen demand and ↑ pulmonary arterial pressure
  • ↑ Intracranial pressure due to increased cerebral blood flow
  • Psychotomimetic effects: hallucinations, nightmares, abnormal EEG (concomitant administration of benzodiazepines is recommended to avoid these effects)
  • Rapid injection or high doses can lead to respiratory depression.
  • ↑ Salivation

Indications

  • Ideal emergency anesthetic for polytrauma patients and other patients with risk of hypotension (no cardiovascular depression)
  • Treatment-resistant asthma
  • Short painful procedures (e.g., fracture reduction)

Ketamine may be administered via intramuscular injection if IV access is not possible!

References:[3][7][8]

Barbiturates

Agents

Mechanism of action

  • Enhanced GABA action enhanced duration of chloride channel opening and hyperpolarization of postsynaptic neurons → ↓ neuronal excitability in the brain
  • High potency, highly-lipid soluble → rapid onset of action due to quick transfer across the blood-brain barrier → brief recovery time due to redistribution into skeletal muscles and adipose tissue

Effects

  • Hypnotic effects
  • ↓ Intracranial pressure due to reduced cerebral blood flow
  • Little to no analgesic or muscle relaxant effects

Side effects

Indications

Contraindications

References:[3][9][10]