Lecture 9: Induction drugs (Exam 2) Flashcards
What are the characteristics of the ideal injectable drug
- Provide reliable sedation, analgesia, & muscle relaxation
- Min changes in CV or respiratory fxn
- Small vol needed
- Wide safety index
- Rapid onset & short duration of action
- Reversible
- Non-cumulative
- Readily metabolized & excreted by the body
- Long shelf life (stable in heat & light)
- Inexpensive
- Ava on the market
- Low potential for human abuse (not a controlled substance)
Fill out the table:
Describe propofol
- Milky white oil in water emulsion
- No preservative (discard open vial w/in 6 hours)
Describe propofol28
has benzyl alcohol preservative but only approved for dogs
What is the MOA of propofol
Activates GABA(a) receptor -> increases Cl conduction & block Na channel -> hyperpolarization (brought in a lot of neg ions) -> CNS depression & loss of consciousness
What are the pharmacokinetics of propofol
- Rapid distribution followed by a slower clearance phase
- Rapid hepatic metabolism & excretion by kidneys (not in cats or greyhounds)
What are the pharmacodynamics of Propofol (CNS, CV, Resp, musculoskeletal, & fetal/neonatal)
- CNS - Decreases intracranial pressure & cerebral metabolism of oxygen (anticonvulsant effects so good for px w/ head trauma)
- CV - Decreases BP due to vasodilation
- Resp - Dose dep respiratory depression & transient apnea (often w/ cyanosis)
- Musculoskeletal - produced muscle relaxation (transient myoclonus can occur)
- Fetal/neonatal - cross placenta but is rapidly cleared from neonate
What is the propofol species specific consideration for grey hounds
Need same dose for induction but the recovery time is longer
What is the propofol species specific consideration for cats
- Caution w/ repeated daily use
- Don’t use propofol28 (can’t process the preservative really well)
What is the propofol species specific consideration for horses
- not really used b/c excitation & vol/cost
- Can be used for CRI
What is the propofol species specific consideration for swine
Does not induce malignant hyperthermia (good drug to use for them)
What is the propofol species specific consideration for small ruminants
- Smooth rapid induction w/ a good recovery
- Possible cost considerations
Describe the clinical scenario of propofol
- Give over 60 - 90 sec
- Swift induction (20 to 30 sec)
- Be ready to ventilate px
- Recover in 2 to 12 mins
- No analgesia
- Possible pain when injecting
What is the characteristics dissociative anesthetics
Dissociation from thalamocortical (consciousness) & limbic (emotion & memory) systems to change awareness (decrease)
What are the two most common dissociative anesthetics
- Ketamine
- Tiltamine
What is the MoA of dissociative anesthetics
- Mainly: via antagonist effects @ NMDA receptors
- Others: AMPA, BDNF, opioid, etc receptors
- Interacts w/ voltage-gated Ca channels
What are the PKs of dissociative anesthetics
- Water soluble (can give in multi different ways)
- Rapid onset
- Short duration
- Highly lipophilic (quickly crosses the BBB)
- Metabolized by the liver & excreted by the kidneys
What are the PDs on the CNS or dissociative anesthetics
- Cataleptic state (not asleep but not responding to external stimuli)
- Can see emergency delirium (ataxia, hyper-reflexive, sensitive to touch, & increased motor activity)
What are the PDs on the CV or dissociative anesthetics
- Direct neg cardia inotropic effects (usually overcomed by sympathomimetic effects)
- Increased BP, HR, cardiac output, myocardial oxygen req, & cardiac work
- Inhibition of NE reuptake (increased plasma catecholamines)
What are the PDs on the resp sys or dissociative anesthetics
- Doesn’t cause sign resp depression
- Bronchial smooth muscle relaxant (bronchodilation & decreased airway resistance)
- “apneustic” resp pattern (prolonged inspiration & rel short expiratory time w/ several shallow breaths taken
- Increased salivation & respiratory tract secretion
What are the PDs on the musculoskeletal sys or dissociative anesthetics
- Can cause muscle rigidity & even spont movements
- IOP can increase after admin (b/c of increased tone of extraocular muscles)
What are the PDs on the Fetal/neonatal or dissociative anesthetics
- Crosses the placenta
- Can cause fetal depression
What are some dissociative anesthetics species specific considerations for dogs
Combine ketamine w/ benzo for induction (can us a alpha 2 agonist or opiod)
What are some dissociative anesthetics species specific considerations for cats
- Can spray into the mouth of fractious cats (can increase salivation)
- Caution w/ use of dissociative in tigers (seizure-like behavior possible)
- ketamine + alpha 2 agonist, benzo, &/or ace for IM
What are some dissociative anesthetics species specific considerations for horses
- Adequately sedate before induction
- Admin ketamine w/ benzo, alpha 2 agonist, or guaifenesin)
- Telazol inductions are smooth but recovery is rough
What are some dissociative anesthetics species specific considerations for ruminants
- ketamine + benzo/guaifenesin
- “ketamine stun” tech (sub anesthetic dose of ket & xylazine given to calves prior to castration
What are some dissociative anesthetics species specific considerations for swine
- Does not induce malignant hyperthermia
- Telazol has a slow calm recovery but not rec for pot belly pigs
Describe the clinical use of dissociative anesthetics
- Typically ketamine + benzo ( or a2 agonist)
- Ket can be given as CRI @ sub anesthetic doses to reduce inhalant req
- Not reversible
- Oral, ocular, & swallowing reflexes are still intact (nystagmus common)
- Use caution w/ px that have hepatic or renal dysfxn
- Scheule 3 controlled sub
- Telazol usually used in shelter med
Describe alfaxalone
- Older formulation was poorly water soluble & caused histamine release in dogs
- New formula w/ non-cremophor (no histamine release & better water solubility) & can give IM/IV
- No antimicrobial preservative
- P450 hepatic metabolism & elimination via kidneys & feces
What is the MOA of alfaxalone
Neuroactive steroid molecule that binds to GABA(A) receptor to increase Cl condution into the cell -> hyperpolarization of postsynaptic membrane -> CNS depression
What are the PDs of alfaxalone (CNS, CV, Resp, Musculoskeletal, & neonatal/fatal)
- CNS - Decreases CBF, ICP, & CMRO2
- CV - hemodynamic stability but can cause dose dep hypotension (b/c of vasodilation)
- Resp - dose dep respiratory depression &/or apnea
- MS - good muscle relaxation
- N/F - Crosses placenta & causes dose dep fetal depression
Describe the clinical use of alfaxalone
- No analgesia
- Used for induction but can also be used as CRI to maintain ax
- Used for px undergoing c-section
- Good induction for dogs that are a poor ax risk
- Can increase IOP in dogs
- No pain on IV injection
- Schedule IV controlled sub
- Transient paddling, excitement in cats, & vocalization in dogs may occur in recovery (rough recovery for horses)
Describe etomidate
- pH of 6.9
- Insoluble in water
- high osmolarity leads to adverse effects
What is the MOA of etomidate
Enhances action of GABA (inhibitory neurotransmitter) @ the GABA(A) receptor -> increased Cl conduction into cell -> hyperpolarization of postsynaptic neuron -> CNS depression & hypnosis
What are the PKs of etomidate
- Rapid penetration of brain (quick induction)
- Rapid redistribution to inactive tissue (fast recovery)
- Large therapeutic index
- Metabolism by liver & plasma esterases
- Excreted in urine
What are the PDs of etomidate (CNS, CV, Resp, Endocrine, MS, N/F)
- CNS - cerebroprotective effects (vasoconstriction of cerebral vessels, reduces CBF, & CMRO2) which leads to cerebral perfusion maintained & decrease in ICP occurs. Decreases IOP
- CV - Min to no change in HR, SV, CO, MAP, & CVP. Baroreceptor fxn & SNS response remain intact (hemodynamic stability)
- Resp - min effects
- Endo - Adrenocortical suppression for up to 5 to 6 H
- MS - myoclonus or tremors
- N/F - min effects
What is the clinical effects of etomidate
- Preferred induction agent for px w/ hemodynamic instability, increased ICP, or cirrhosis
- No analgesia
- Caution for px w/ addison’s or highly stressed px
- Doesn’t appear to be cumulative but not recommended as a CRI b/c of adrenocortical suppression & possible RBC damage
- Premed dose of benzo can decrease myoclonus
What are the side effects of etomidate
- Pain on injection
- Vomiting
- Excitement
- Cats - drooling/salivation & concern for IV hemolysis
When are mask/chamber inductions used
- Exotics
- Very aggressive px where injectable anesthetics are not possible
What should be noted about mask or chamber inductions
- Use caution b/c of exposure to personnel & potential to harm px
- They are not considered the standard of care in most situations
What are some other combos that can be used for induction
- Opioid induction (fent + benzo)
- Ket + propofol
- Guaifenesin + ket
- Guaifenesin + ket + xylazine
- Guaifenesin + thiopental
- Propofol + thiopental
- Ket + xylanzine
- Telazon + ket + xylazine/dexmed
- Ket + alfaxalone
