Veterinary Anesthesia Severna Park Veterinary Hospital Aug. 6, 2014 Rebecca Krimins, DVM, MS Advanced Anesthesia and Pain Management for Animals

Topics Anesthetic drugs Pre-anesthetic combinations Monitoring anesthetic depth

Ketamine Dissociative: dissociate the thalamocortic and limbic systems  cataleptoid state (eyes open, swallow reflex intact) Muscle rigidity Decreases cardiac contractility Increase peripheral vascular resistance  decreases cardiac output

Ketamine NMDA-antagonistic properties (blocks glutamate) Helpful with superficial pain, not useful for deep or chronic pain (poor visceral analgesia) Helps prevent sensitization (windup) of nociceptive pathways

Ketamine Rapid onset (~ 5 minutes) Moderate DOA (1-2 hours) Stimulate sympathetic tone  increased HR and BP Induce salivation and airway secretions Pain upon IM injection (low pH) Some dogs show emergence delirium (uncoordinated movements of head/neck, voacalizations, salivation, agitation)

Ketamine Pre-anesthetic Dosage Dogs: 1-3 mg/kg IV, IM, SQ Cats: 3-10 mg/kg IV, IM, SQ

Ketamine CRI dosage for intra-op pain: – 0.5 mg/kg IV bolus – 10 ug/kg/min CRI (lower doses for post-op) Apnea in some (but generally is NOT a respiratory depressant) Don’t administer with an anticholinergic Associated with premature ventricular depolarizations

Tiletamine Dissociative More potent than ketamine (3X), longer DOA Produces sedation, immobility, amnesia, analgesia, muscle rigidity (Zolazepam: similar to diazepam but is water soluble and more potent; can cause prolonged recovery in cats)

Ketamine/valium and Tiletamine/zolazepam Different neuroactive agents used  induce anesthesia with the goal of achieving the highest quality of anesthesia with minimal side effects Ketamine/valium – Ketamine 5 mg/kg IV – Diazepam 0.25 mg/kg IV Tiletamine/zolazepam: (2-8 mg/kg IV, IM) – DOA: 20 min to one hour – Limited shelf-life after reconstitution – Induction: 1-3 mg/kg IV or 6-8 mg/kg IM

Telazol Difference in Dogs vs Cats Dogs: get a tiletamine hangover Cats: get a zolazepam hangover

Ket/Val (or Telazol) vs Propofol Compared to propofol: – Less muscle relaxation – Increased salivation – Increased dysphoria Good cardiopulmonary support – HR, CO, BP well maintained Short duration

Propofol 2,6,-diisopropylphenol Propofol: soybean oil, glycerol, egg phosphatide Propoflo-28: benzyl alcohol White emulsion: shake thoroughly (don’t mix with other drugs) Metabolized by liver, extrahepatic sites of metabolism

Propofol Induction dose: 4-8 mg/kg IV Microdose under GA: 1-2 mg/kg IV Titrate to effect Duration of action: minutes Advantages: rapid induction of GA, rapid metabolism, rapid emergence from GA, low incidence of nausea/vomiting

Propofol Disadvantages – Hypotension and cardiac depression – Respiratory depression – Pain on injection – Heinz body anemia in cats (repeated use)

Dexmedetomidine α-2 adrenergic agonist Properties: sedative-hypnotic, analgesic, muscle relaxation – Anxiolysis, calming Stimulate α2 receptors in brain  decreased norepinephrine release Dose-dependent CV effects: vasoconstriction  hypertension  reflex bradycardia

Dexmedetomidine Dosage: dependent on patient and procedure – IM: 5 ug/kg – IV: 1-2 ug/kg Rapid onset (~ 5 minutes) Moderate duration (~2 hours) Atipamezole (reversal): – Give same volume as dexmedetomidine IM, SQ, IV

Hydromorphone and Morphine Pure mu opioids; excellent analgesics Both drugs can cause excitement when used alone, in young, healthy animals Both drugs will slow heart rate (increased vagal efferent activity) and cause respiratory depression Profound sparing effect with induction and maintenance agents

Hydromorphone vs Morphine Hydromorphone: – SQ route associated with vomiting & panting – Doses > 0.1 mg/kg may produce hyperthermia – DOA: 1-4 hours Morphine: – Can cause vomiting – Associated with histamine release – Excitement in cats – Metabolites excreted by the kidneys – DOA: 2-4 hours Pupil size: miosis and mydriasis – Miosis (dogs) – Mydriasis (cats)

Hydromorphone and Morphine Hydromorphone dosages (SQ, IM, IV) – SQ: 0.1 mg/kg (DOA: 1-4 hours) – IV: 0.05 mg/kg (DOA: 1-2 hours) Morphine (SQ, IM, IV) – IM: mg/kg – IV: mg/kg Naloxone (reversal) 1-10 ug/kg IV – Take 1 ml naloxone, dilute with 9ml saline, titrate 1 ml/min to effect

Pre-anesthetic Combinations Think about: – Procedure: surgical vs diagnostic vs other – Level of pain involved in procedure – Duration of procedure – Patient status – How much time do you have

Pre-anesthetic Combinations Opioid +/- benzodiazepine +/- α2- agonist +/- phenothiazine +/- anticholinergic

How to Monitor Anesthetic Depth No single parameter tells you how light/deep – Gather all information together (patient, normals, disease states, drugs, procedure type and duration) Must know parameter normals in order to be able to identify abnormals – Temp, pulse, RR, BP – SBP > 140 mmHg = light – SBP < 80 mmHg = deep

How to Monitor Anesthetic Depth Interact with patient Every 5 minutes, check palpebral reflex (corneal reflex) and jaw tone; position of eye; check for signs of movement, muscle twitching, neck tone Maintain body temperature Vaporizer setting for past 15 minutes = ?

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