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
What are 4 common IM combinations of dissociatives?
- ketamine, dexmedetomidine, butorphanol (kitty magic)
- telazol, butorphanol, dexmedetomidine
- telazol, morphine, dexmedetomidine
- telazol, ketamine, xylazine
What is an extremely useful low-risk induction combination?
- Ketamine 2 mg/kg
- Propofol 2 mg/kg
- mix in same syringe and give IV to effect or give ketamine then propofol
(still requires a solid premed!)
What is an extremely useful higher risk induction combination?
- Midazolam 0.3 mg/kg
- Ketamine 3 mg/kg
- Fentanyl 7 mcg/kg
- mix in same syringe and give IV to effect or give midaz, ketamine, then fentanyl
What is alfaxalone? What is its mechanism of action?
Class IV controlled neuroactive steroid (progesterone analog)
GABA receptor agonist
How dose alfaxalone compare to propofol?
- same rapid action and given to effect
- can be given IM or IV, with less irritation extravascularly
What are 5 major advantages to alfaxalone over propofol?
- cardiosupportive - less hypotension
- patients maintain respiratory rate
- can be used IM in cats and small dogs
- can be given repetitively, especially in cats
- can be give in CRI
How is alfaxalone given IM?
- with an opioid +/- midazolam
- with an opioid +/- dexmedetomidine
(no discomfort on injection)
Is the major advantage to the use of alfaxolone groups over other induction agents?
maintains highest heart rate and mean/systolic BP, allowing for the best oxygen delivery in patients
- best means of preserving cardiovascular function
What is the current suggested IV dosing for alfaxalone induction?
2 mg/kg to effect in premedicated cats or dogs for induction
What are the current suggested feline IM dosing of alfaxalone TIA in healthy/low risk cats and high/unknown risk cats?
3-4 mg/kg with an opioid and dexmedetomidine 5-10 mcg/kg or acepromazine 0.03 mg/kg
2 mg/kg with an opioid and midazolam 0.2 mg/kg
What is the current suggested IM dosing of alfaxalone TIA in dogs?
2.5 mg/kg with an opioid and dexmedetomidine 5 mcg/kg
What are 5 cases in which alfaxalone is especially useful?
- C-sections
- exotics
- repetitive boluses or CRI in cats
- brachycephalics
- higher risk anesthesia - cardiovascular or respiratory disease
What is etomidate? What are 2 mechanisms of action?
non-controlled hypnotic solution in propylene glycol
- increased Cl conduction via binding to GABA complex
- hyperpolarizes postsynaptic nerve endings
What is etomidate’s largest advantage?
MINIMAL EFFECTS
- causes little change in HR, BP, or CO
- does not sensitize the heart to catecholamines
- does not cause histamine release
What are 5 major precautions to using etomidate?
- expensive
- hyperalgesic and CNS stimulation
- causes myoclonus
- painful on any administration
- related to adrenal insufficiency due to reduced steroid synthesis
In what patients is increased mortality associated with use of etomidate? In what situation is it most commonly used?
septic and trauma patients
cardiocritical patients —> hemodynamic stability during induction
What are the 3 mechanisms of action of barbiturates?
- increased GABA binding to GABA receptor
- blocked glutamate binding to GABA receptor
- activates RAAS system
What 4 barbiturates are used as induction agents?
- pehnobarbital
- thiopental
- methohexital
- thiobutabarbital
(ultrashort acting!)
How does barbiturate redistribution cause cumulative effects?
initially goes to vessel-rich tissues, but is then stored in fat, slowing down metabolism and prolonging effect
How are barbiturates administered? Why?
IV
alkaline solution causes pain, hair loss, redness, and slough/limb necrosis in perivascular areas
Why must barbiturates be carefully mixed with other medications?
pH incompatibility leads to precipitate formation
- like thiopental and lidocaine
What is the major advantage to using barbiturates as induction agents?
very kind to the CNS - lowers cerebral metabolic rate and blood flow, making it neuroprotective
How do barbiturates compare to propofol and ketamine? What are 3 precautions?
- rapid-acting, but slower
- slow metabolism due to redistribution
- moderate respiratory depression
- hypotension due to third spacing of IV volume to mesentery and splenic enlargement (careful with abdominal surgery)
- arrhythmias, like ventricular bigeminy common
What is most commonly recommended for low-risk patients for induction?
- ketamin + benzo
- propofol
- alfaxaline (IM)
What is most commonly recommended for high-risk patients for induction?
- alfaxalone
- fentanyl, diazepam/midazolam, propofol
- fentanyl, diazepam/midazolam, ketamin
- fetofol
- etomidate
How do induction and inhalation agents cause anesthesia?
- induction agents induce shock
- inhalation agents maintain shock
potent, yet necessary poisons
What is essential for emergency drug preparedness?
- calculations performed ahead of time
- ensure amounts are clearly visible
- know anesthesia arrest doses vs classic CPR doses
epinephrine 0.05 mg/kg
atropine 0.02 mg/kg
naloxone 0.02 mg/kg
atipamezole equal to dexmed volume
How are IV catheters checked? What is avoided? What route is the best?
palpate proximal vein while giving saline flush
withdrawal - can induce vasculitis and valvular adhesion
direct - avoids ventricular effect from IV line
What should be done before giving any induction medications? Why?
baseline pulse and respiration rates
- assess how quickly to deliver induction
- gives an idea of premed benefits and cardiopulonaryneuro state
- gauges how much induction agent to deliver to effect and level of inhalant necessary to start patient on
When compared to other agents, Alfaxalone administration will result in…
a. higher heart rate
b. higher postoperative temperature
c. higher mean arterial blood pressure
d. A and B
e. A, B, and C
C —> cardioprotective with best oxygen delivery
Ketamine and Telazol provide a cardiostimulatory effect that may be useful for induction of all the following disease scenarios and signalments EXCEPT:
a. early DCM in a Labrador Retriever
b. mild mitral valvular disease in a middle-aged toy poodle
c. mild mitral insufficiency in an aged mixed breed dog
d. hypertrophic cardiomyopathy in a 16 y/o DSH
D
Etomidate will cause all the following systemic effects for normovolemic patients except:
a. hypotension
b. reduced endogenous steroid synthesis
c. CNS stimulation
d. burning vascular pain
e. myoclonal activity
A
Telazol is a combination of which 2 agents?
a. tiletamine and ketamine
b. tiletamine and zolazepam
c. propofol
d. zolazepam and benzodiazepine
e. diazepam and tiletamine
B
What is the most important assessment that should be performed prior to administration of induction medications?
a. palpebral reflex present
b. obtain baseline pulse and respiratory rate
c. check oxygen flow rate
d. IV catheter present
B
Alfaxalone can be administered repetitively to feline patients without risk of Heinz Body anemia occurring. Is this true or false?
TRUE
repetitive propofol causes Heinz body anemia
Your veterinary technician colleague does not want to give morphine for pain control due to fear of the patient vomiting. Instead she says that the propofol will provide sedation AND analgesia for the patient. Is she correct?
NO —> induction agents do not provide analgesia
Which of the following is most correct? Inhalants are not used to induce anesthesia because:
a. they provide costly, inaccurate, uncontrolled and environmentally/personnel agent entry into general anesthesia
b. patients are too calm to show painful behavior
c. cause rapid induction and quick recoveries
d. benign to the patient’s repsiratory system
A
The goal of inducing a veterinary patient with an intravenous induction agent is to get them from stage __ to stage __as smoothly and efficiently as possible.
I to III
True or false: Induction agents cause a controlled form of cardiovascular “shock” while inhalant agents maintain a controlled form of cardiovascular “shock.”
TRUE
All of the following agents EXCEPT which one, have a mechanism of action at the GABA receptor complex?
a. etomidate
b. alfaxalone
c. ketamine
d. propofol
C
True or false: Alfaxalone is likely to result in greater hypertension post-administration compared to propofol.
FALSE —> cardioprotective, causes less hypotension
