VPT 321: Veterinary Neuropharmacology (2+1)

Dissociative anaesthesia

DISSOCIATIVE ANAESTHETICS

• The drugs that cause the patient to feel dissociated from or unaware of the surroundings during induction are called dissociative anaesthetics.
• Dissociative anaeasthetics depress the cerebral cortex before causing medullary depression.
• Dissociative anaesthesia 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 anaesthesia 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 dissociatives are dose dependent.