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33 Cards in this Set

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What type of drugs start out as a liquid, converted in the vaporizer to gas, and inhaled and absorbed via the pulmonary capillaries?
Inhalational anaesthetic agents
___ is an indication of a liquid's evaporation rate; relates to the tendency of particles to escape from a liquid
Vapor pressure or equilibrium vapor pressure
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
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
The more insoluble an INHALATIONAL agent is, _______________?
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
Saturated vapour pressure is the equilibrium point and is dependent on what two things?
SVP dep. on temperature and atmospheric pressure

SVP increases with increasing temperature
Which inhalational agents have a large blood: gas coefficient?
Soluble inhalational agents
What factors determine the extent a tissue takes up anaesthetic?
Depends on blood supply
and surface area of tissue
What two effects influence the inspired concentration?
Concentration effect
Second gas effect
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
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!)
What inhalational agent is somewhat irritating to respiratory tract?
isoflourene
What inhalational agent are very similar to isoflourene, but more expensive?
sevoflurane
most effective absorption surface in the body?

why?
pulmonary alveolar epithelium

huge surface area...duh
do inhalation agents have pre- OR post-synaptic effects?
have BOTH pre- and post-synaptic effects
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
What inhalational drug produces metabolite known as 'Compound A' on reaction with soda lime?
Sevoflurane

Compound A has no clinical significance...aside from causing renal necrosis in rats.
for most inhalational agents, SVP is low OR high?
for most inhalational agents, SVP is very HIGH – this is why vaporisers are required
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
Which 2 inhalants have ~same SVP?
halothane 239 mm Hg
isoflurane 240 mm Hg
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
If blood:gas ratio/coefficient is 2:1 or 2; which holds higher concentration - blood or gas?
BLOOD

this is principle behind "Solubility partition coefficients"
and blood:gas solubility
blood:gas solubility/coefficient is 0.5, what is ratio of blood:gas?
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
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!)
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
Minimum alveolar concentration or MAC describes what ?
is a concept used to compare the strengths, or potency of anasthetic..at this conc. 50% patients do not respond to stimulus
High MAC means?
Drug is poor anesthetic, it is measure of potency (higher value means higher concentration needed to anesthetize animal)


Speed of onset faster?! (wrong)
Which has higher MAC: 1. halothane
2. desflurane 3. methoxyflurane
desflurane (MAC = 8) > halothane > methoxyflurane (0.23)

desflurane = least potent anesthetic; also fastest onset
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
Fi:FA ratio is what?
comparing inspired concentration (Fi) to alveolar (FA) concentration of anaesthetic

uptake is determined by the rate and depth of ventilation
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
Why is important to minimize the amount of inhalation agents used?
All suppress cardiovascular and respiratory centers; so can kill animal very easily
What are some factors that decrease MAC?
Narcotics
Sedatives
Tranquilizers
Nitrous oxide
Age
Hypothermia
Pregnancy