• Clinical science

Intravenous anaesthetics

Abstract

Intravenous anesthetics are used to induce a state of impaired awareness or for 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 analgetic 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, see the corresponding learning card.

Overview

Indication Characteristics
Propofol
  • Total Intravenous Anaesthesia (TIVA) - drug of choice
  • Sedation in ICU
  • Short procedures
  • Rapid induction
Etomidate
  • IV anaesthesia for patients with hemodynamic instability
Arylcyclohexylamine (e.g., ketamine)
  • Ideal emergency anaesthesia for polytrauma patients
  • Short painful procedures (e.g., fracture reduction)
  • Treatment-resistant asthma
Barbiturates (e.g., thiopental)
Opiates (e.g., fentanyl, morphine)
  • Analgesia during induction and/or maintenance anaesthesia
  • Muscle rigidity
  • Cardiovascular and respiratory depression
Benzodiazepines (e.g., midazolam)
  • IV anaesthesia induction
  • Short outpatient procedures
  • Preoperative sedation
  • Endoscopy
  • ↓ Blood pressure
  • Anterograde amnesia

References:[1][2][3]

Propofol

Mechanism of action

  • Propofol's mechanism of action is not yet fully understood
  • Rapid onset and recovery

Effects

Side effects

Indications

  • Standard for anaesthesia induction
  • Total intravenous anaesthesia (TIVA)
    • A technique for induction and maintenance of general anaesthesia using IV drugs alone
    • Propofol is the drug of choice; especially for patients with an intermediate to high risk for PONV

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

Etomidate

Mechanism of action

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

Effects

Side effects

Indications

  • Anaesthesia for patients with hemodynamic instability

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

References:[3]

Ketamine

Mechanism of action

Effects

Side effects

  • ↑ 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

Mechanism of action

Effects

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

Side effects

  • Hypotension (dose-dependent)
  • Respiratory depression and/or apnea (dose-dependent)
  • Laryngospasm, bronchospasm (histamine release)
  • Myoclonus
  • Painful injection
  • Dependence
  • Cytochrome P450 induction
  • Contraindicated in porphyria
  • Accidental intra-arterial injection of barbiturates
    • Pathophysiology: Incorrect injection of barbiturates can cause tissue necrosis or even gangrene (through vessel injury, spasm, and thrombosis) because the anesthetic is administered in a strongly alkaline solution.
    • Treatment
      • Intra-arterial dilution with NaCl 0.9%
      • Terminate vessel spasm
        • Intra-arterial administration of 5–10 mL of 1% lidocaine
        • Axillary plexus or stellate ganglion block
      • Intra-arterial heparin injection as thrombosis prophylaxis

Indications

Barbiturate overdose

References:[3][9][10]