Concept of Dissociative Anesthesia
The key feature of the drug is the induction of dissociative anesthesia. This term refers to a functional dissociation within the central nervous system: certain brain structures are depressed while others remain active.
The clinical presentation of this anesthesia differs significantly from classic general anesthesia. Consciousness is only partially lost, accompanied by a mild hypnotic effect and amnesia. True surgical anesthesia is not achieved.
Unlike other agents (e.g., propofol or etomidate), ketamine produces pronounced analgesia. Crucially, vital functions are preserved:
- Respiration: The patient breathes spontaneously; the respiratory center is not depressed.
- Reflexes: Protective laryngeal, pharyngeal, and cough reflexes remain fully intact.
- Musculoskeletal system: Muscle tone is not reduced (the drug does not cause significant myorelaxation).
Mechanism of Action and Pharmacokinetics
The pharmacodynamics are based on the blockade of NMDA receptors. Acting as an antagonist at these receptors, the drug prevents the excitatory effects of the neurotransmitter glutamate on various structures of the central nervous system.
The molecule is highly lipophilic. This property allows the substance to rapidly cross the blood-brain barrier (BBB) and exert a prompt therapeutic effect. The drug is used primarily for induction of anesthesia, as well as an independent analgesic agent for short, highly painful procedures (a prime example being the debridement of extensive burn surfaces).
Onset and duration of the effect depend heavily on the route of administration:
| Route of Administration | Onset of Action | Duration of Effect |
|---|---|---|
| Intravenous | 30–60 seconds | 5–10 minutes |
| Intramuscular | 2–6 minutes | 15–30 minutes |
Effects on the Cardiovascular System
This agent has a unique characteristic among its drug class: it is the only non-inhalation anesthetic that exerts a stimulating effect on the cardiovascular system.
Key hemodynamic effects include:
- Increased heart rate (HR).
- Increased cardiac output.
- Increased blood pressure (BP).
This cardiostimulatory effect develops quite rapidly. Peak blood pressure and heart rate values are recorded 2–4 minutes after administration, after which a gradual decline begins, returning to baseline within 10–20 minutes. The mechanism underlying this stimulation involves the activation of sympathetic innervation combined with the inhibition of neuronal norepinephrine reuptake.
Side Effects and Complications
Despite its high efficacy and safety regarding respiratory function, its widespread clinical use is limited by specific central nervous system side effects.
In the postoperative period (during emergence), patients frequently experience:
- Psychomotor agitation.
- Vivid, often frightening dreams and nightmares.
- Pronounced hallucinations.
The high risk of such postoperative emergence reactions requires mandatory pharmacological management. To mitigate these adverse effects, the premedication or co-administration of diazepam is used in clinical practice.