Injectables/TIVA Flashcards
Why shouldn’t a patient with a coagulopathy who is anemic and hypovolemic recieve acepromazine?
it is a vasodilator which also affects platelet aggregation and decreases the number of circulating erythrocytes by causing splenic relaxation
Define pharmacokinetics
the study of absorption, distribution, metabolism, and excretion of administered drugs
Define pharmacodynamics
The study of the effects caused by a drug to the body
Volume of distribution is what?
how much the central compartment of the patient will dilute the drug administered
- Vd = dose/[plasma concentration after 1 minute of a single bolus]
The central compartment refers to what group of organs/vessels?
great vessels, heart, lungs, and aorta
Why is it that liposoluble drugs have a large volume of distribution?
due to the first pass uptake from the central circulation (especially the lungs), therefore decreasing final plasma concentration
How do you calculate a bolus dose?
Bolus dose = Vd x [Desired Plasma Concentration]
Why is it important to saturate all tissues (other than the target tissue - CNS) prior to setting a CRI?
because all of these tissues have some degree of liposolubility and therefore hinder the rise of plasmatic concentration and effect
Which tissues are considered the rich vessel group?
Heart, lungs, splanchnic viscera, kidneys and CNS
Why does fat require a very long period of time to significantly change plasma concentrations?
because it has a very limited blood supply
What is the purpose of the loading bolus?
should be able to bring the plasmatic concentration to the therapeutic level and at the same time saturate all the distribution tissues of the body
What is the principle of a constant rate infusion?
To maintain plasmatic concentration of a drug by matching the infusion rate to the elimination rate of the drug
What are the primary side effects of opioids?
- Respiratory depression
- interfere with thermoregulation: cause paradoxic mild hypothermia (dogs) or hyperthermia (cats)
- paradoxic excitation (cats, horses, cattle); sedation (dogs, monkeys, people)
- Nausea and vomiting (>> morphine)
- miosis (dogs); mydriasis (cats)
- defecation followed by constipation
- increase in ADH release (decreased urination); suppression of detrusor muscle/urge sensation (epidural)
- dose-dependent bradycardia
- Vasodilation and decr BP (morphine and mepiridine d/t H2 release)
What clinical situations are opioids good for?
- Sick patients
- Cardiovascular compromised patients
- Septic patients
- Elderly patients
In which situations should you be careful using opioids?
- Brain lesions: resp depression, vomiting
- Sick sinus syndrome
- Severe AV block
What are the advantages of using opioids?
- great for analgesia
- minimal deleterious CV effects
- no decr in myocardial function
- reversible
Why should diazepam not be mixed in the same syringe with any other drugs (with the exception of ketamine)?
because it’s propylene glycol saturate may cause precipitation to occur
Why might you use benzos?
- Minor tranquilizers causing mild sedation
- used to reduce dose requirements of other drugs
- cause mild muscle relaxation
- have minimal CV or resp side effects
- reversible
Why might midazolam be preferable to diazepam?
- diazepam injections are painful at administration and has unpredictable IM and SQ absorption, so is used only IV; cannot be mixed with other drugs
- midazolam is water-soluble, can be mixed, and administered IM, SQ or IV
What is one downside to benzos?
they can cause excitation, particularly in healthy cats (less so in sick animals)
T or F: Dissociative agents, such as ketamine and telazol, can be used as premeds as well as induction agent
true; can help with chemical restraint in difficult patients as premeds
Ketamine is broken down by hepatic metabolism in dogs and horses. Can it still be used in patients with liver failure?
yes, as the drug will still be redistributed, so breakdown and clearance will just be much slower; however, do not use ketamine CRIs in liver failure patients
What are the side effects of ketamine?
- Sympathetic stimulation —> incr HR and BP
- Apneustic breathing
- Apnea
- Maintain laryngeal reflexes
- Increase salivation and mucus (DO NOT use atropine to fix)
- Poor muscle relaxation
Ketamine is good to use for what types of patients?
- Young/healthy
- Difficult (IM) - esp. cats
- Painful procedures and animals
- Exotics
Ketamine is contraindicated in what situations?
- HCM
- Renal disease in cats (b/c excreted unchanged)
- Arrhythmias
- Head or corneal trauma (increases IOP/ICP)
- Glaucoma
- seizures (lowers threshold)
- emergency patients
Due to its moderate somatic analgesia by NMDA antagonism, ketamine reduces release of the neurotransmitter glutamate on the dorsal horn, decreasing what?
wind up
What are the advantages of propofol?
- Short half-life (quick induction/recoveries)
- hepatic and extra-hepatic metabolism
- protects against increases in ICP
- decreases CMRO2
What are some side effects of propofol?
- Sympatholytic effects: decr in BP, CO, SVR (vasodilation)
- Apnea
- Seizure-like activity (myoclonus)
- Splenic engorgement
What can happen if a cat receives 6 consecutive days of propofol anesthesia?
Malaise and Heinz body anemia
What patients/procedures are good for propofol use?
- Lar par (substitute for thiopental)
- brain tumors (CRI) - due to low cerebral metabolic rate
- increased ICP or IOP
When should you not consider using prop?
- splenectomies
- laparoscopies
- CV compromise
- hypotensive or hypovolemic patients
What are the advantages of using Etomidate?
- Minimal CV side effects
- CNS friendly
What are the potential side effects of etomidate?
- Hemolysis (propylene glycol -> high osmolality)
- Adrenal suppression (Addisonian crisis)
- Myoclonus
- Poor muscle relaxation - usually combined w/ benzos or opioids
What patients would etomidate be a good choice for?
- Cardiac dz
- CV instability
- Brain lesions (increased ICP)
When should you consider not using etomidate?
- Sepsis (Euadrenal syndrome)
- Addisonian crisis
- Anemia
Why might you choose alfaxalone over propofol?
- It can be given IM
- Induction is smoother
What are the side effects of alfaxalone?
- Mild decrease in BP and SVR
- Increase in HR and increase OR decrease in CO (dose dependent)
- myclonus and paddling
- splenic engorgement
- apnea (EVEN WITH IM INJECTIONS)
In what patients is alfaxalone a good choice?
- Most patients for induction
- ICP and IOP
- TIVA
In which cases should you be careful using alfaxalone?
- Hypotension/hypovolemic
- Laparoscopy
- Splenectomy
- CV compromise
