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33 Cards in this Set
- Front
- Back
What type of drugs start out as a liquid, converted in the vaporizer to gas, and inhaled and absorbed via the pulmonary capillaries?
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Inhalational anaesthetic agents
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___ is an indication of a liquid's evaporation rate; relates to the tendency of particles to escape from a liquid
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Vapor pressure or equilibrium vapor pressure
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In confined space, there equilibrium in which number of molecules entering the gaseous state equals the number leaving it.
This is called ________? |
saturated vapour pressure (SVP)
At this point, vapour pressure is at a maximum for the liquid |
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If an inhalational agent has a high SVP (saturated vapor pressure), then ________?
what inhalational anesthetic has highest SVP? (excluding N2O) |
Very volatile agent (SVP is also temperature dependent)
Desflurane has highest SVP |
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The more insoluble an INHALATIONAL agent is, _______________?
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The quicker you can change its concentration in the body
MORE INSOLUBLE AN INHALATIONAL ANAESTHETIC AGENT, THE FASTER IS WORKS FOR BOTH INDUCTION AND RECOVERY |
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Saturated vapour pressure is the equilibrium point and is dependent on what two things?
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SVP dep. on temperature and atmospheric pressure
SVP increases with increasing temperature |
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Which inhalational agents have a large blood: gas coefficient?
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Soluble inhalational agents
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What factors determine the extent a tissue takes up anaesthetic?
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Depends on blood supply
and surface area of tissue |
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What two effects influence the inspired concentration?
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Concentration effect
Second gas effect |
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Which inhalational agents have a LOW blood: gas coefficient: soluble or insoluble?
Example? |
Insoluble agents = LOW blood:gas coeff.
(e.g. desflurane) Remember the more INSOLUBLE an inhalational anaesthetic agent, the FASTER it works for both induction and recovery |
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What inhalational agent causes big drop in blood pressure?
Therefore you would NOT this agent in ___? |
Halothane
avoid in sick, or animals with foreign object, liver disease blas blas..because reduces organ perfusion (except cranium!) |
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What inhalational agent is somewhat irritating to respiratory tract?
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isoflourene
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What inhalational agent are very similar to isoflourene, but more expensive?
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sevoflurane
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most effective absorption surface in the body?
why? |
pulmonary alveolar epithelium
huge surface area...duh |
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do inhalation agents have pre- OR post-synaptic effects?
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have BOTH pre- and post-synaptic effects
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True or False:
* inhalation agents never interact with the neuronal plasma membrane * do not act via second messenger systems |
FALSE:
* inhalation agents DO interact with the neuronal plasma membrane * they may also act via second messenger systems |
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What inhalational drug produces metabolite known as 'Compound A' on reaction with soda lime?
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Sevoflurane
Compound A has no clinical significance...aside from causing renal necrosis in rats. |
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for most inhalational agents, SVP is low OR high?
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for most inhalational agents, SVP is very HIGH – this is why vaporisers are required
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What inhalation agent is highest?
Which is lowest? |
desflurane 664 mm Hg <-- you can pack a whole lot more of this guy into confined space, than you can sevofl.
sevoflurane 160 mm Hg |
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Which 2 inhalants have ~same SVP?
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halothane 239 mm Hg
isoflurane 240 mm Hg |
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At sea level and room temperature, which can you achieve higher concentrations of : isoflurane, sevo, or desflurane?
What do vaporizers do? |
At sea level and room temperature, you can achieve concentrations of :
21% sevo 32% halothane 32% isoflurane 86% desflurane Vaporisers are used to deliver SAFE anaesthetic concentrations of inhalational agent |
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If blood:gas ratio/coefficient is 2:1 or 2; which holds higher concentration - blood or gas?
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BLOOD
this is principle behind "Solubility partition coefficients" and blood:gas solubility |
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blood:gas solubility/coefficient is 0.5, what is ratio of blood:gas?
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1:2 or 2:4, etc.
insoluble agents have a LOW Blood/Gas co-efficient; remember this means works faster! > do NOT confuse this with SVP |
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body can be considered to consist of four basic groups, based on PERFUSION and PROPORTION OF BODY MASS
(determines how quickly take up drug and reach eq.) |
1. Vessel rich->75% perfusion (% of CO)
2. Muscle/skin->19% perfusion 3. Fat->6% 4. Vessel poor (ie. CT, bone)->0% perfusion (see next question!) |
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The vessel-rich group is composed of?
Speed to eq.? Why? |
brain, heart, liver, kidneys, endocrine glands and splanchnic bed.
Perfused well, have smaller volume (like compared to muscles), so rapidly reach equilibrium |
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Minimum alveolar concentration or MAC describes what ?
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is a concept used to compare the strengths, or potency of anasthetic..at this conc. 50% patients do not respond to stimulus
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High MAC means?
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Drug is poor anesthetic, it is measure of potency (higher value means higher concentration needed to anesthetize animal)
Speed of onset faster?! (wrong) |
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Which has higher MAC: 1. halothane
2. desflurane 3. methoxyflurane |
desflurane (MAC = 8) > halothane > methoxyflurane (0.23)
desflurane = least potent anesthetic; also fastest onset |
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Key factors determining _____?:
* blood:gas solubility * Fi:FA ratio * cardiac output * partial pressure difference between alveolus and venous blood (PA - PV) |
Key factors determining anaesthetic uptake into blood
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Fi:FA ratio is what?
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comparing inspired concentration (Fi) to alveolar (FA) concentration of anaesthetic
uptake is determined by the rate and depth of ventilation |
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What is second gas effect?
Hint: Function of nitric oxide |
Because [NO] is so insoluble, take up rapidly and concentrates other drugs in alveoli, so increases speed they're taken up as well
can use LESS of other inhalation drugs |
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Why is important to minimize the amount of inhalation agents used?
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All suppress cardiovascular and respiratory centers; so can kill animal very easily
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What are some factors that decrease MAC?
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Narcotics
Sedatives Tranquilizers Nitrous oxide Age Hypothermia Pregnancy |