Dissociative anesthetics in animals

Dissociative anesthetics in animals cause the patient to feel dissociated from or unaware of the surroundings during induction are called dissociative anaesthetics. Dissociative anaesthetics depress the cerebral cortex before causing medullary depression.

Dissociative anesthesia is a state whereby profound somatic analgesia is combined with a light plane of unconsciousness, but the animal seems to be dissociated from its environment. Pharyngeal, laryngeal, corneal and pedal reflexes the abolition of which, are conveniently used to assess the depth of anesthesia persist relatively unimpaired and the eyes remain wide open. These drugs are characterized by analgesia and superficial sleep.

Somatic analgesia is good while visceral analgesia is poor. Muscle relaxation is poor. Catalepsy is noticed with rigidity and partial extension of the limbs. These drugs rapidly cross the placental barrier and affect the foetus.

Dissociative anaesthetics are contraindicated in animals with head trauma or space occupying lesion in the brain, corneal ulcers and laceration.

In humans, dreams and emergence of hallucinations are the features of its use and the adminstration of dissociative anaesthetics is largely restricted to younger children.

Dissociative anesthetic agents increase muscle tone, spontaneous involuntary muscle movement (occasionally seizure), salivation, lacrimation are also increased. Cardiovascular effects of dissociates are dose dependent.

Examples of Dissociative anesthetics in animals are ketamine, tiletamine and Phencyclidine.

Dissociative anesthetic drugs

Ketamine

Ketamine causes profound analgesia, immobility, amnesia with light sleep, and feeling of dissociation from one’s own body and surroundings. Primarily acts on the cortex. Inhibits glutamate receptor, analgesia partly through opioid receptors. May interfere with  glutamate and NMDA receptors.  Can be given both intravenous and intramuscular route of drug administration.

On anesthesia some reflexes remain active – cough, pharyngeal etc. hence may not be suitable for surgeries for endoscopy or oropharyngeal surgery. Good for brief operations and repeated use.

Ketamine presented as 5 ml or 10 ml vials (100 mg / ml). No drug accumulation notice for ketamine. Rapidly metabolized by liver (metabolite – norketamine – hypnotic – long standing drowsiness and prolonged recoveries in large doses)

Central stimulation of sympathetic system stimulation of CVS (tachycardia, high BP), Large doses direct depression of myocardium, Produces good analgesia, Increased muscle tone. So muscle relaxant needed.

Tiletamine

Tiletamine is a more potent, longer acting and have greater side effects. Tiletamine + zolazepam combination is found to be useful.