9b – Induction and Injectable Anesthetics Flashcards
Propofol
- Acts on GABAa recepotrs in CNS to produce anesthesia
- Induction is smooth and rapid
- Short duration of action depends on REDISTRIBUTION
- Recovery is fast and smooth
- Used for induction and maintenance (TIVA): minimal accumulation
- No analgesia
Propofol induction is smooth and rapid
- Onset 40-90s
- One does lasts 5-10mins
Propofol when injecting: pain/damage
- Occasionally pain upon IV injection
- NO tissue damage if injected perivascular
Propofol vehicle
- Lipid emulsion=WHITE
o Will grow bacteria=discard within 24hrs of opening
PropoClear (propofol)
- Lipid free formulation
Propoflo 28 (propofol)
- Contains preservative (May be toxic for cats!)
- Labelled for use up to 28 days after opening
Propofol: CV effects
- Depression is dose dependent
- Myocardial depression
- Venodilation=decrease BP
- *RESETS baroreceptor reflex: increase HR with a drop in BP does NOT occur (only last 10mins)
- AVOID in hypovolemic animals and cardiac disease patients
Propofol: respiratory system effects
- Depression is DOSE dependent
- Post: induction apnea and cyanosis
- Supplement O2, pre-oxygenate
- Mild bronchodilation
Propofol on induction and/or recovery can occasionally see in dogs
- Paddling movements
- Opisthotonus
- Twitching
Propofol is recommended for
- C-sections
- Cerebroprotection: reduces cerebral blood flow and cerebral metabolic rate
- Patients with compromised LIVER function
Propofol in cats
- Reduced capacity for glucuronide conjugation
- Propofol infusion=recovery from anesthesia delayed
- Repeated administration over several days
o Hemolysis and Heinz body formation - *can use it on cats still
Alfaxalone
- Acts on GABAa receptors in CNS
- Induction smooth and rapid
- Short duration depends on REDISTRIBUTION
- Fast recovery (quality improves with premedication)
- Used for induction and maintenance (TIVA)
- NO analgesia
- NO pain or tissue damage
Alfaxalone: smooth and rapid induction
- Onset: 15-45seconds
- One dose lasts: 5-10mins
Alfaxalone vs. Propofol
- Longer shelf life (open for 30 days)
- Clear solution
- Can be administered IM
Alfaxalone CV effects
- Depression Is DOSE dependent
- Hypotension: combo of myocardial depression and some peripheral vasodilation
- Compensation via reflex tachycardia (baroreceptor reflex)
Alfaxalone respiratory system affects
- Depression is DOSE dependent
- Post-induction apnea
Alfaxalone effects
- Good muscle relaxation
- Produces reliable sedation in cats when give IM
- Excellent in reptiles (IM)
Co-induction when using alfaxalone OR propofol to minimize amount required: typical agents included are
- Benzodiazepines (Midazolam or Diazepam)
- Ketamine
Ketamine
- Dissociative anesthetic agent
o Interrupts info reaching higher centers in the brain - Comes in a racemic mixture
How is ketamine different from GABAa agonist drugs?
- Cateleptoid state with slow nystagmus
- Muscle rigidity with higher doses
- Maintains CN reflexes (gag, swallow, palpebral and central eye in dogs and cats)
Ketamine and vet med
- Popular
- Used for INDUCTION and MAINTENANCE and ANALGESIA
- *profound analgesic (somatic>visceral, wind up pain)
- Neither anti- or pro-convulsant
- *AVOID IN CATS with renal function
Ketamine onset and duration
- Onset: 30-90s
- Duration: 20-30mins (longer)
Ketamine can be administered
- IM
- IV
- SC
- TM
Ketamine: mechanisms of action
- NMDA receptor antagonist
- CNS voltage dependent Na, K, Ca channels
- Depression of CNS acetyl choline receptors
- Some action at GABAa receptors
- Depression of nociceptive cells in dorsal horn of spinal cord
Ketamine causes muscle rigidity so
- ALWAYS combine with a muscle relaxant (ex. benzodiazepine OR alpha2-agonist)
Ketamine: auditory and visual stimuli distributed during recovery to cause
- Emergence delirium
Ketamine use with other drugs to reduce side effects
- Alpha2 agonists
- Benzodiazepines
- Acepromazine
CV system: ketamine
- Healthy animals=indirect mild CV stimulation
- Sympathomimetic effects for 2-15mins
- Increase in cardiac work and myocardial oxygen consumption
- AVOID in CATS with hypertrophic cardiomyopathy
CV system: ketamine with critically ill patients OR catecholamine depleted
- May see mild direct myocardial depressant effects
Respiratory system: ketamine
- Minimal respiratory depression
- Bronchodilation
- Laryngeal and pharyngeal reflexes preserved
- Irregular/periodic breathing pattern: apneustic breathing
Behavioural side effects: ketamine
- Can cause rough recoveries
o Head shaking, vocalization, dysphoria, salivation
When combining drugs with ketamine the major goals
- Decrease amount of ketamine needed
- Eliminate unwanted side effects (improve recovery quality)
- Produce good skeletal muscle relaxation
- Improve visceral analgesia
- Prolong period of anesthesia/immobilization
Ketamine/diazepam (‘Ket-Val’)
- IV induction agent: dogs, cats, neonatal foals, horses, calves, cattle
- Slow onset (30-90s)
- Short acting, rapid recovery
- *MINIMAL CV and respiratory side effects
- *do NOT use for C-sections (diazepam accumulates in neonates)
Alpha2 agonist + ketamine examples:
- Xylazine + ketamine
- Dexmedetomidine – ketamine – opioid
Xylazine + ketamine
- Good combo for large animals or wildlife immobilization
- Analgesia, muscle relaxation, narcosis
- Potent cardiopulmonary depression
- NOT recommended for routine use in cats and dogs
Dexmedetomidine – ketamine – opioid
- Wildlife, game ranch animals
- Supportive care
- Monitor closely
- Alpha2 reversible
Induction apnea
- Usually observed after rapid bolus of IV induction agent
- Once IV induction is redistributed=animal wakes up
- Assist ventilation until spontaneous ventilation returns
- Once induction agent wears off=inhalant plasma concentration should be enough to keep them anesthetized
- Apnea can be avoided by titrating to effect
Apnea or hypoventilation result in
- Poor uptake of maintenance inhalant anesthetic
- Poor transition to maintenance phase (stable plane) or inhalant anesthesia
Guaifenesin
- Only used for sedation and muscle relaxant effects
