Anesthetic Induction Flashcards
What happens during anesthetic induction?
Sleep induction
Skeletal muscle relaxation
Loss of reflexes
Endotracheal intubation
What is the ultimate goal of anesthetic induction?
Controlled anesthesia
How do we judge an animal that is at stage 3 anesthesia?
Loss of righting reflex
Not surgical plane
What are the stages of anesthesia?
Stage 1: analgesia
Stage 2: disinhibtion
Stage 3: surgical anesthesia
Stage IV: medullary depression
How can you get the animal calm before induction?
Premedication
Why do you want the animal calm before induction?
Stress increases epinephrine levels Elevates sympathetic tone Epinephrine is arrythmogenic Fight or flight Poor inductions leads to poor recoveries
Do most induction drugs have a low or high therapeutic index?
Low (narrow safety margins_
How much should be given of induction drugs?
Give to effect, so until the animal is unconscious and can be intubated
What would the ideal anesthetic agent be?
Smooth loss of consciousness Analgesia and relaxation Wide safety margin Not controlled Minimal to no metabolism Inexpensive But does not exist
What are the injectable induction agents?
GABA agonists
NMDA antagonists
Opioids
What are the GABA agonists?
Propofol
Etomidate
Alfaxalone
Thiopental (C-III controlled substance)
What are the NMDA antagonists?
Ketamine
Telazol (tiletamine-zolazepam)
What is the mechanism of action of thiopental?
Bind to GABAa receptor and enhance GABA effect and directly stimulate causing increased chloride current and hyperpolarization
Reduces CMRO2, ICP, and CBF but preserves CPP due to greater drop in ICP than MAP
What are the effects of thiopental?
Respiratory depression
Arrhythmias, hypotension
No analgesia
What is the technique for giving thiopental?
Small animals: one-half as initial bolus
Wait 30 seconds
Titrate to effect
Large animals: give entire calculated dose
What is the mechanism of action for propofol?
Hypnotic
Enhances GABA inhibition
Mild NMDA inhibition
Does propfol provide analgesia?
No
How is propofol metabolized?
Extra-hepatically
What is the onset of action IV for propofol?
10-30 seconds
What is the duration of action of propofol?
3-7 minutes
What is the drug of choice for C-sections? Why?
Propofol
Crosses the placenta, but clears rapidly from neonatal circulation
What are the cardiovasulcar side effects of propofol?
Vasodilation –> hypotension
Bradycardia
Impaired baroreceptor response
What are the pulmonary side effects of propofol?
Decreased respiratory rate and tidal volume
Apnea
What does propofol cause at induction?
Excitement
What kind of metabolism does propofol undergo?
Both hepatic and extra-hepatic
What redistribution does propofol undergo?
Extensive and rapid tissue redistribution
What happens to cats with every day dosing of propofol?
Hemolysis
Lethargy
Anorexia
What is a propofol/ketamine mix?
Reduced dose of each
50:50 mix in same syringe
Rapid, reliable, effective, chemically stable, bacteriostatic
What is the technique of administering propofol?
Slow IV over 30 to 60 seconds
If it is too fast, the will have apnea, cyanosis, and bradycardia
Flow by O2
What is alfaxalone?
Neuroactive steroid that enhances GABA inhibition
Does alfaxalone provide analgesia?
No
What are the cardiovascular side effects of alfaxalone?
Cat: decreased HR and BP
Dog: marked increased HR, no change in BP
What are the pulmonary side effects of alfaxalone?
Decreased RR (Apnea) Decreased tidal volume (minimal)
What does alfaxalone cause at recovery?
Excitation
What are ketamine and tiletamine?
NMDA antagonists
Dose-dependent restraint to anesthesia
What is the onset of ketamine and tiletamine?
60 seconds after IV, 5-10 minutes after IM, SC
What are the effects of ketamine?
Long-lasting motor effects after IM
Poor relaxation alone (add tranquilizer, benzodiazepines)
Inadequate analgesia for acute pain with single dose
What is telazol?
A combination of tiletamine HCl (NMDA antagonsit) and zolazepam HCl (benzodiazepine)
What do high dosages of Telazol lead to?
Prolonged recovery
What is Telazol commonly mixed with for injectable anesthesia?
Alpha-2 agonist and ketamine
What is etomidate?
GABAa agonist
Non-barbiturate sedative-hypnotic injectable anesthetic agent
What is the clinical use of etomidate?
Cardiac animals
What is the technique for etomidate?
Give slow IV, titrate
Administer with IV fluids to decrease pain
Patient must be well sedated before use
Rapid onset, short duration
What are the effects of etomidate?
Minimal effects on cardiovascular
Respiratory function maintained
Suppresses adrenocortical steroidogenesis
What are opioid combinations used in?
Debilitated dogs
What can opioid combinations produce?
Bradycardia
Cardiovascular stability
What are examples of opioid combinations?
Hydromorphone, fentanyl, methadone + diazepam or midazolam IV
What is guaifenesin?
Centrally-acting muscle relaxant used as an anesthetic adjunct in large animals
What are the effects of guaifenesin?
Very irritating with acidental perivascular injection
What inhalational agents are useful for induction?
Isoflurane
Sevoflurane
Desflurane
When should you use caution with inhalation agents?
With stressed animals due to high epinephrine levels
What is chamber induction used for?
Small animals/exotics
Small, really upset animals
What is the oxygen flow rate like in chamber induction?
High
What is the inhalant concentration like in chamber induction?
High
What is mask induction used for?
Pocket pets, birds/exotics, neonates, and pediatrics
What do you do after anesthetic induction?
Intubate
Connect breathing system
Turn on vaporizer
Check vital signs- airway, breathing, circulation
