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 articles
Overview
| Overview of intravenous anesthetics [1] | |||
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| Indications | Mechanism of action | Adverse effects | |
| Propofol |
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| Etomidate |
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| Ketamine |
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| Barbiturates (thiopental and methohexital) |
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| Opioids (e.g., fentanyl, morphine) |
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| Benzodiazepines (e.g., midazolam) |
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Propofol
Mechanism of action
- Not fully understood; propofol is thought to act as an agonist on GABAA receptors and sodium channels of the reticular formation, and as an NMDA receptor inhibitor.
- Rapid onset and recovery
Effects
- Hypnotic effects
- Antiemetic
- Antipruritic
- Anticonvulsant
- Bronchodilation
- ↓ Intracranial pressure
- No analgesic or muscle relaxant effects
Side effects
- Hypotension (dose-dependent)
- Respiratory depression (dose-dependent)
- Anaphylaxis (esp. in patients with allergies to soy or egg products )
- Pain on injection
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Propofol infusion syndrome
- Etiology: high doses and prolonged administration of propofol
- Clinical features: severe metabolic acidosis, rhabdomyolysis, renal failure, and/or cardiac failure (often fatal)
- Diagnostics: Patients undergoing prolonged propofol treatment should have triglycerides monitored at least every 3 days, as increased triglyceride levels correlate with development of propofol infusion syndrome.
- Management: discontinue propofol immediately, symptomatic treatment
Indications
- Standard for anesthesia induction
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Total intravenous anesthesia (TIVA)
- A technique for induction and maintenance of general anesthesia using IV drugs alone.
- Propofol is the drug of choice, especially for patients with an intermediate to high risk of postoperative nausea and vomiting (PONV).
References:[4][5]
Etomidate
Mechanism of action
- Enhances GABAA receptor function in the reticular formation
- Rapid onset and recovery
Effects
- Hypnotic effects
- ↓ Intracranial pressure
- Anticonvulsant effects
- Little to no effect on the cardiovascular system [2]
- No analgesic or muscle relaxant effect
Side effects
- Transient acute adrenal insufficiency (due to adrenal cortex suppression → reduced cortisol production)
- Postoperative nausea and vomiting
- Painful injection (avoid by administering an opioid prior to injection)
- Myoclonus
Indications
- Anesthesia for patients with hemodynamic instability
Ketamine
Mechanism of action
- NMDA receptor antagonist
- Belongs to the arylcyclohexylamines class
- Rapid onset
Effects
- Dissociative anesthesia: unique anesthetic state with analgesia, intact spontaneous breathing, amnesia, and no complete loss of consciousness
- Strong analgesia
- Bronchodilation
- Sympathomimetic effects: ↑ blood pressure, ↑ heart rate, ↑ cardiac output
- Increases cerebral blood flow
Side effects
- Nystagmus
- ↑ Oxygen demand and ↑ pulmonary arterial pressure
- ↑ Intracranial pressure due to increased cerebral blood flow
- Acute psychotomimetic effects: disorientation, hallucinations, vivid dreams, nightmares, and/or 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)
- Treatment-resistant depression [3]
Ketamine may be administered via intramuscular injection if IV access is not possible!
References:[6][7]
Barbiturates
Agents
- Thiopental
- Methohexital
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
- Hypotension (dose-dependent)
- Respiratory depression and/or apnea (dose-dependent)
- Laryngospasm, bronchospasm (due to histamine release)
- Myoclonus
- Painful injection
- Visual hallucinations
- Vivid dreams
- Bradycardia, arrhythmias
- Cytochrome P450 induction
Indications
- IV anesthesia induction; (esp. short procedures with minimal pain and high risk of raised intracranial pressure)
- Reduction of intracranial pressure for brain edema following trauma or surgery
- Sedation for electroconvulsive therapy (e.g., methohexital)
- Convulsion during or after anesthesia
Contraindications
- Hypersensitivity
- Severe cardiovascular decompensation; conditions in which a decrease in blood pressure would be hazardous
- Porphyria
- Addison disease
- Liver or kidney disease
- Severe anemia
- Thyroid disorders
- Myasthenia gravis
- Asthma
References:[8]