Exam 2: Pharmacology, Uptake and Distribution of Inhaled Anesthetics Flashcards
What is the important physical property of inhaled anesthetics when it comes to your patient?
Blood/Gas coefficient
Low partition coefficient= Low solubility= Less uptake by blood and tissues (go to sleep faster, wake up faster)
Desofluorane likes to come out te blood quickly, isofluroane will stay longer. Sevofluroane is metabolized the most and has some transformation - not indicated in patients with kidney disease.
What are the three main inhalation anesthetics used in veterinary medicine?
*rememeber, these are vapors not gases except N2O
sevofluorane, desofluorane, isofluroane
desofluorane boils off at room temperature
What is MAC and what does it tell you?
MAC, minimum alveolar concentration - how we talk about what the dose IS. Prevents gross purposeful movement in 50% of subjects to a supramaximal noxious stimulus.
It means 50% of patients will need less OR more to not respond.
Why is Nitrous oxide not used often in our veterinary species?
The MAC is so high, it cannot be achieved.
What factors decrease and increase MAC?
Decrease: other drugs causing CNS depression, hypothermia, severe hypotension, increasing age, severe hypoxia/hypercapnea
Increase: Hyperthermia and Ephedrine is a good drug to wake up your patients, it causes CNS stimulation.
What are the general side effects of inhaled anesthetics?
decreased alveolar ventilation, CO (contractility, vascular resistance(vasodilation)), renal blood flow and urine output.
INCREASED cerebral blood flow
Under ventilation, what PCO2 and apneic index number should you start trying to do something?
70
2.5-3.5 (MAC)
Desfluroane makes you apnic sooner than others (more potent)
isofluroane is easy to turn up too high
What is maligant hyperthermia?
Malignant hyperthermia: most often seen in pigs.
Associated with halothane and a muscle relaxant (but all inhalants are not off the hook). Has been triggered by an MRI (magnet warms them up). If this happens, take them off gas.
What is the difference between low and high solubility of a (inhalant) drug in relation to uptake by blood and the brain?
Low soluble drugs accumulate in the lungs and very little goes into blood, but what makes it into the blood does not want to be there so it happily pops off into the brain. Will also go opposite direction from brain to lungs to be exhaled.
If it’s highly soluble, it does not stay in the lungs and goes into blood but then it wants to stay there.
highly soluble inhalants (isofluorane), the more it goes into blood, slower rise of alveoli, slower rate of rise of concetration in the brain. longer to sleep, longer to wake.
poorly soluble (desofluroane) induction and recovery is faster. rapid to get into and out of brain. (need higher percent)
If a patient is apnic and you take them off ventilation, will the concentration change?
No, because they are not breathing on their own. The drugs require ventilation for induction and recovery.
Patients ventilating more, alveolar concentration goes up faster. Because replacing gas in alveoli faster. If patients aren’t breathing, there will not be a change. If patient starts apnic, will not get gas into them. These drugs reqire ventilation for induction and recovery.
Why does high CO slow the change in alveolar concentration?
Because the blood is stealing your drug.
Higher blood flow, higher output states, slower change in alveolar ventilation.
How does solubility affect inhalent PA?
Higher solubility = slower rate of change. Need to know an hour ahead of time in high soluble anesthetics to turn off gas because takes patient a long time to wake up.
What is the time constant for a non-rebreathing circuit?
Time constant for non rebreathing circuit? 0. Changes immediately.
What are the advantages and disadvantages of a semi-open, low flow, and closed circuit anesthesia? Which one is most appropriate for any given situation?
Semi open
Advantages:
Easier to Maintain
More rapid changes in circuit
concentration
Don’t need O2 monitoring
Disadvantages:
Waste of O2/inhalants
Patient risk if pop-off closed
Theater contamination
Low flow
advantages:
Less anesthetic gas waste
Less O2 waste
Slow rate of change of inhalant
Concentration
Disadvantages:
More math ;)
Need to change O2 flow rate
more often
Should use O2 monitoring
Closed circuit
advantages:
Less anesthetic gas waste
Less O2 waste
Slow rate of change of inhalant
concentration
disadvantages:
Must pay attention to circuit
O2 flow rate can change
during procedure
Should use O2 monitoring
