Dissociative Anesthetic Objectives – Flashcards

- Ketamine - Tiletamine

- Dissociative anesthetics disrupt pathways involved in consciousness and unconsciousness rather then causing generalized CNS depression (cataleptoid state) - In other words some areas of the CNS are stimulated and some are depressed - Patient is unresponsive to pain and somewhat unconscious but appears alert due to open eyes (cateleptoid state) - Reflexes are maintained during dissociative anesthesia including pharyngeal and laryngeal reflexes. Also the eyes are open and the pupil is dilated during anesthesia

- Dissociative anesthesia - Analgesia - Possible Seizures - Low anesthetic doses stimulate respiration while large doses depress respiration - Bronchodilation - Increases tracheobronchial secretions - Cardiovasdcular stimulation increases cardiac output, central venous pressure and heart rate - The effect on peripheral vascular resistance (vasodialtion) is variable but CO, HR and CVP are all increased - Ketamine is also thought to have a depressant effect on the myocardium that can sometimes be overridden by the central stimulation of the heart - May have an antiarrythmic action - Increases cerebral blood flow and therefore increased ICP - Increased intra ocular pressure - Stimulates salivary secretion - ANS = Increases sympathetic drive and decreases vagal tone

NMDA receptor antagonist

It prevents central sensitization (dorsal horn wind up)

- Somatic analgesia

- Stimulation of the sympathetic system and a vagolytic effect - These effects tend to override the direct myocardial depression causes by dissociative anesthetics

- Myocardial depression

- Metabolized in liver and excreted in kidneys. Cats excrete more unchanged drug in the kidney

- IV, IM

- Approved in cats and nonhuman primates - Anesthetic for minor surgery - Preanesthetic and as induction agent when used with tranqualizer - Chemical restraint and immobilization in many species - Analgesic can use at low doses to avoid cateleptiod state

- Respiratory depression at high doses - Muscle tremors and hypetonicity - CNS stimulation and possible convulsive seizure - Vomiting - Hypersalivation - Pain following IM injection (acidic in solution) - Prolonged recovery - Avoid in patients with cardiac disease - Avoid in patients with hypertension - Careful in patients with liver disease (metabolized by liver) - Careful in patients with kidney disease (due to partial elimination in kidneys, in particular cats due to increased renal elimination) - Avoid in head injuries (due to increase in ICP) - Avoid in animals with epileptic seizures (due to possibility of seizure generation) - Avoid in Glaucoma (due to increased IOP) - Other contraindications reported for tiletamine include pancreatic disease, cesarean section and is not recommended during pregnancy

Atropine and glycopyrolate

Phenothiazine, benzodiazepine, alpha 2 agonist

- Despite the fact it is a cardiovascular safe drug it is contraindicated in patients with cardiovascular disease. These patients often have maximal sympathetic tone and therefore ketamine sympathetic stimulation may cause further tachycardia and increased vascular resistance (vasoconstriction). This has the potential to increase in myocardial oxygen demand

Patient with cardiovascular instability associated with poor sympathetic tone (late decompensated shock, shock due to cardiovascular depression by other drugs, septic shock etc..). If patient has good sympathetic tone (hemorrhagic shock, heart failure etc..) ketamine is not likely to be of benefit in may increase cardiac work

- Ketamine has no specific agonist like benzodiazepines and alpha 2 agonist - Some non specific CNS stimulants may help to reverse ketamine effects - A combination of 4 AP and yohimbine IV partially antagonizes IM ketamine in cats - 4-AP IV is an antagonist to xylazine-ketamine anesthesia in horses - Tolazoline IV antagonizes a combination of IM xylazine and IM ketamine in the African elephant

- Combination of tiletamine and zolezapam

- Cats