Induction Agents Flashcards
What are 3 important characteristics of IV induction agents?
- crosses BBB quickly - lipophilic and unionized at blood pH
- water-soluble - non-irritating
- maintain cardiac output - allows travel to where blood flow is greatest (brain)
What is anesthetic induction? Why is premedication so important?
delivering an anesthesia agent that produced profound cerebral and cardiopulmonary depression and momentary unconsciousness
induction agents are rarely analgesic
What are the 4 stages of general anesthesia? What is the goal of induction agents?
(pre-medicated = semi-awake, but sedated)
1. disoriented, struggling, reflexes present
2. excitement, struggling, reflexes exaggerated
3. unconscious, diminished or absent reflexes
4. very close to death, action required to resuscitate
get patient from Stage I to III safely and quickly
What are 5 reasons why inhalants aren’t used to obtain unconsciousness?
- slow, often bronchoirritating
- not precise or controlled
- patients are often struggling
- irritating and dangerous to patient/staff
- expensive
What way of induction is avoided? Why?
inhalant masking and caging
- OSHA violation
- uncontrolled and stressful
- increases intracranial pressure
- GI and air inspiration likely
- causes cardiovascular depression
What are 3 advantages and disadvantages to using IV anesthetics?
ADVANTAGES:
1. simple and rapid
2. no special equipment
3. non-irritating to airways
DISADVANTAGES:
1. veins can be harder to access
2. require IV catheter
3. apnea, hypotension, and excitement are possible
What is propofol? What are 2 mechanisms of action?
non-controlled sedative hypnotic agent in 1% oil emulsion, making it very soluble in fat (water insoluble - irritating!)
- enhancement of GABA receptor CI conductivity
- NMDA receptor inhibition modulates Ca influx
How is propofol commonly given? What does it not provide?
provides smooth entry and recovery —> given IV in increments to effect (or titrated); only IV, but less irritating perivascularly
analgesia
What allows for rapid wakening of patients on propofol?
redistributed from blood to muscle to fat and metabolized very quickly to allow for rapid elimination
- half life = 1/5 of an hour (12 mins)
What are 4 major disadvantages to using propofol?
- respiratory depression or apnea (give slowly!)
- cardiovascular hypotension
- can irritate or burn on injection
- may act as an incubation medium for organsism, so it must be discarded within 6-24 hours of opening
What is an exception to the necessity of discarding propofol quickly after use?
Propoflo 28 (benzyl alcohol)
In what patients does propofol need to used carefully?
adds to overall lipid load —> pancreatitis, hyperlipidemia, hepatic lipidosis
How does propofol affect RBCs?
causes hemoglobin oxidative changes that result in frail RBCs
- especially in cats due to their increased reactivity of hemoglobin with more sulfhydryl groups (methemoglobinemia, then Heinz body formation)
What dose is recommended for propofol in patients without premedication? With premeds?
NO PREMEDS = 4-6 mg/kg IV, Plumb dose (increased liability)
PREMED = 2-3 mg/kg IV, reduces necessary dose (lessened liability)
What 3 premeds offer the largest reduction in propofol dosage? Least?
- Acepromazine
- Dexmedetomidine
- either with an opioid (+++)
Midazolam
What dissociatives can be used as induction agents?
- ketamine
- tiletamine (found in Telazol)
What is ketamine? Where does it act? What other 3 receptors does it act on?
controlled dissociative agent that is acidic in solution and water soluble (less irritating!)
hippocampal formation and prefrontal cortex non-competitive NMDA antagonist
- Mu and Sigma opioid receptors
- monoamines
- VG Ca channels
How does ketamine differ from propofol? How is it most commonly used?
can be given IM or IV —> stings outside of vessels, but will not cause sloughing
tends to be used initially for immobilization and analgesia, as well as unconsciousness
What is ketamine commonly administered with? Why?
benzodiazepines
tends to cause excitement (sympathomimetic) in doses >4-5 mg/kg or as a solo agent
What is telazol? What is its mechanism of action?
tiletamine and zolazepam = controlled dissociative anesthetic and benzo in a lyophilized powder requiring reconstitution
SAME AS KETAMINE
- hippocampal formation and prefrontal cortex non-competitive NMDA antagonist
- also acts on Mu and Sigma opioid receptors, monoamines, and VG Ca channels
How does Telazol compare to ketamine? In what situation is it commonly very useful?
- more potent due to tiletamine’s higher potency and addition of a BZD
- ratio of zolazepam and tiletamine cannot be altered. unlike ketamine and valium or midazolam
feral cats and larger dogs - volumes for injection are small (very potent!)
What are dogs at higher risk for developing if Telazol is used?
tetany (dogs > cats)
What is the preferred route of administration of dissociatives? What 5 things should be looked out for?
IV —> painful any other way
CAUSES NEURONAL RELEASE OF CATECHOLAMINES
1. increased muscle tone
2. myocardial stimulant
3. bronchoconstriction
4. increased cerebral metabolism, blood flow, and ICP
5. mild respiratory stimulation
In what 2 patients are dissociatives used with caution (very low dose) or not at all?
- cardiomyopathy
- intracranial disease, especially space-occupying masses
How are the downfalls of dissociatives avoided?
MULTIMODAL REGIMES - combined with other drugs so their doses can be lowered substantially
What are 5 common IV combinations of dissociatives?
- ketamine and propofol (ketofol)
- ketamine and diazepam
- ketamine and midazolam
- ketamine, midazolam, fentanyl
- Telazol and dexmedetomidine