Keyword
Ketamine
Mechanism
CNS effect
Ketamine produces dose-related unconsciousness and analgesia. The anesthetized state has been termed dissociative anesthesia.
The duration of ketamine anesthesia after a single IV administration of a general anesthetic dose (2 mg/kg) is 10 to 15 minutes, and full orientation to person, place, and time occurs within 15 to 30 minutes.
Pupils dilate moderately, and nystagmus occurs. Lacrimation and salivation are common, as is increased skeletal muscle tone, often with coordinated but seemingly purposeless movements of the arms, legs, trunk, and head.
Respiratory effect
Ketamine has minimal effects on the central respiratory drive as reflected by an unaltered response to carbon dioxide. There can be a transient (1 to 3 minutes) decrease in minute ventilation after the bolus administration of an induction dose of ketamine. Unusually large doses can produce apnea, but this is seldom seen.
Ketamine is a bronchial smooth muscle relaxant.
Cardiovascular effect
Ketamine also has unique cardiovascular effects; it stimulates the cardiovascular system and is usually associated with increases in blood pressure, heart rate, and cardiac output.
Uses and Doses of Ketamine
Side effect
Patients with increased ICP and with intracranial mass lesions breathing spontaneously should not receive ketamine because it can increase ICP.
Ketamine may be contraindicated in patients with an open eye injury or other ophthalmologic disorder, in which a ketamine-induced increase in intraocular pressure would be detrimental.
Psychiatric disease, such as schizophrenia, also is contraindications. One also should consider carefully using ketamine when there is a possibility of postoperative delirium from other causes.
References
Miller’s Anesthesia, 7th edition, Ch. 26