Anesthetic Induction Flashcards
Anesthetic induction components
- sleep induction
- skeletal muscle relaxation
- loss of reflexes
- endotracheal intubation
_____ is necessary for all patients undergoing inhalant anesthesia, or to give patient oxygen
Endotracheal intubation
- need to lose laryngeal reflexes
- may go nasally in large animals
Anesthetic induction
Safely transfers a patient from a state of conscious sedation to a chemically induced coma
- ultimate goal = controlled anesthesia!!
How do we judge an animal is at stage 3 anesthesia?
Loss of righting reflex
- NOT surgical plane
Surgical plane
Patient will not respond or respond minimally to surgical procedures
Stages of anesthesia
- stage 1: analgesia
- stage 2: disinhibition
- stage 3: surgical anesthesia
- stage 4: medullary depression
Eyes are _____ during anesthesia
Medially ventrally rotated
Stress ______ epinephrine levels
Increases
- elevated sympathetic tone
- epinephrine is arrhythmogenic
- fight or flight
- poor inductions = poor recoveries
Induction drugs
Most have low therapeutic index (narrow safety margins)
- give to effect, until the animal is unconscious and can be intubated
“To effect”
Decrease in laryngeal effect to intubate
- not done in horses/wildlife –> give full amount of drug
Ideal anesthetic agent
- smooth loss of consciousness
- analgesia and relaxation
- wide safety margin
- not controlled
- minimal to no metabolism
- inexpensive
- doesn’t exist
GABAa agonists
Work similarly to endogenous GABA in the brain to induce a sleep state
- propofol
- etomidate
- alfaxalone
- thiopental
NMDA antagonists
- ketamine
- telazol
Opioids
Used in patients that are very sick
- very depressed patients do not need a lot to enter sleepy state
Thiopental
Ultra short acting barbiturate
- rapid 30 sec onset
- rapid tissue redistribution
- rapid recovery 15-30 min
- bind to GABAa receptor and enhance GABA effect (low doses) and directly stimulates (high doses) = increased chloride current and hyperpolarization
- reduces CMRO2, ICP, and CBF but preserves CPP due to greater drop in ICP than MAP
Thiopental - side effects
- respiratory depression
- arrhythmias, hypotension
- controlled substance (3)
- no analgesia
- rough and prolonger recoveries in sighthounds (cumulative)
Propofol
Substituted isoproylphenol (soy lecithin base)
- hypnotic: enhances GABA inhibition, mild NMDA inhibition
- no analgesia
- extra hepatic metabolism (can still be used in liver failure patients)
Propofol - action
- onset of action IV: 10-30 sec
- duration: 3-7 min
Propofol emulsion
Alkylphenol relatively insoluble
- emulsion containing soybean oil, glycerol and purified egg phosphatide
- pH is 7.0-8.5 (bacterial growth will occur if contaminated)
Propofol - pros
- excellent relaxation
- non-cumulative
- useful in sighthounds due to minimal body fat
- crosses placenta but clears rapidly from neonatal circulation (drug of choice for C sections)
Propofol 28
- less expensive
- old version no preservative - promotes bacterial growth
- 2% benzyl alcohol
- significant respiratory depression
- no analgesia
Propofol side effects
- cardiovascular: vasodilation –> hypotension, bradycardia, impaired baroreceptor response
- pulmonary: decrease RR and tidal volume, apnea
- excitation at induction
Propofol - metabolism
Both hepatic and extra-hepatic metabolism
- extensive and rapid tissue redistribution
- cats: every day dosing leads to hemolysis, lethargy, anorexia
- cats have prolonged recovery after single dose if sick
Propofol/ketamine mix
Reduced dose of each
- 50:50 mix in same syringe
- rapid, reliable, effective, chemically stable, bacteriostatic
Propofol - technique
Slow IV
- over 30-60 seconds
- too fast: apnea, cyanosis, bradycardia
- flow by O2
Alfaxalone
Neuroactive steroid
- progesterone derivative
- cyclodextrin
- enhances GABA inhibition
- no analgesia
- non-cumulative
Alfaxalone side effects
- cardiovascular: decreased hr and bp in cat, increased hr, no change in bp
- pulmonary: decreased rr and tidal volume
- excitation at recovery
Ketamine and tiletamine
NMDA antagonists
- dose dependent restraint to anesthesia
- onset: 60 sec after IV, 5-10 min after IM, SC
- useful in many species
- NOT recommended in cats with HCM!!
- DEA class 3
Ketamine
Common, wide safety margin
- inexpensive
- IM, SQ, IV, rectally, orally
- DEA 3 (highly addictive)
Single use ketamine
- long lasting motor effects after IM
- poor relaxation alone, add tranquilizer
- inadequate analgesia for acute pain with single dose, add analgesic drug +/- CRI
Ketamine combinations
Versatile drug = IM, SC, slowly IV to effect in small animals
- do not titrate in large animals
- combine with benzo
- light sedation –> general anesthesia
- free ranging wildlife
Telazol
Combo of tiletamine HCL (NMDA antagonist) and zolazepam HCl
- high doses lead to prolonged recovery
- commonly mixed with alpha2-agonists and ketamine for injectable anesthesia
Etomidate
GABAa agonist
- non-barbiturate sedative hypnotic injectable anesthetic agent
- clinical use = cardiac animals
Etomidate - technique
- give slow IV, titrate
- administer with IV fluids to decrease pain
- patient must be well sedated before use!!!
- minimal effects on cardiovascular
- respiratory function maintainedd
- expensive
- not controlled
- rapid onset, short duration
Etomidate - method of action
Propylene glycol diluent
- myoclonus: use tranquilizers to minimize
- suppresses adrenocortical steroidogenesis
- avoid in Addisonian and immune compromised and extremely sick animals!
Opioid combinations
- useful in debilitated dogs
- unreliable induction in other species
- cardiovascular stability
- reversible
- used most often in sick patients!! (fentanyl, remi-fentanyl)
Opioid combo - technique
Must give slowly!!
- quiet environment, prone to dysphoria
- may produce bradycardia
- hydromorphone, fentanyl, methadone+diazepam or midazolam (IV)
Guaifenesin
Centrally-acting muscle relaxant
- used as anesthetic adjunct in large animals
- large volumes required (induction dose 55 mg/kg IV)
- very irritating, accidental perivascular injection (will slough)
Inhalational agents for anesthetic induction
Iso, sevo, desflurane
- useful after premed or alone
- not good for adult large animals
- not to be used routinely
Inhalational agents
Caution in stressed animals (high epinephrine levels)
- environmental pollution
- slow onset, excitation likely (stage 2 anesthesia)
- mask or chamber
Chamber induction
Small animals/exotics
- small, really upset patients
- high O2 flow rates
- high inhalant concentrations
- monitor closely until animal becomes recumbent
- remove from chamber and continue delivery via mask
Chamber induction technique
Easy, single agent
- wasteful and causes pollution
- no ready access to animal in case of emergency
- prolonged excitation phase (stage 2)
Mask induction
Common in pocket pets, birds/exotics
- neonate and pediatrics
- ideal in neonates, very young patients
- tight fitting mask
- restraint often necessary
What to do first after anesthetic induction?
- intubate
- connect breathing system
- turn on vaporizer
- check vital signs: airway, breathing, circulation
