Propofol: A highly lipophilic GABA agonist that may be used for long-term sedation. Disadvantages include vasodilation, which can result in hypotension and an increase in serum triglycerides and lipase.
Etomidate: A GABA agonist that has the advantage of being the most hemodynamically neutral. It does not cause changes in heart rate, blood pressure, or cardiac output. However, it inhibits cortisol synthesis, which can lead to (reversible) adrenocortical suppression. Because of this, it is often avoided in patients with septic shock, and it should not be used as maintenance of sedation after induction.
Ketamine: An N-methyl-d-aspartate antagonist that is similar to PCP, it preserves the respiratory drive during induction of anesthesia. Ketamine also provides an analgesic effect. It stimulates the release of catecholamines, which can cause bronchodilation but also increase heart rate, myocardial contractility, and cerebral blood flow.

Ketamine

Mechanism of action

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

↑ 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)

Ideal emergency anesthetic for polytrauma patients and other patients with risk of hypotension (no cardiovascular depression)