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What is the latent heat of vaporization?
# cal required to change 1 gram of liquid into a vapor at a given temp
Is vaporization temp dependent?
What happens to vaporization when there is no heat source?
Vaporization process stops because the liquid cools.
What is the source of heat for vaporization for volatile agents?
Liquid itself (most volatiles, molecules in constant motion (per kinetic molecular theory) supplies heat for vaporization) or an external source (desfluorane)
At what T is vapor pressure measured at?
RT which is 20 degrees C
What does VP depend on?
- Temp (in the room)
- Identity of the liquid
What is boiling point?
That temp when VP = atm P
What does volatile mean?
How does Dalton's Law apply to a vaporizer?
- What's in the vaporizer exerts a partial pressure. For example, if iso and O2 in a container together at atm P, iso's VP =
- 240 (VP of iso) / 760 (atm P)= 0.31 (partial pressure)
What is the VP of halothane and iso?
What is the VP of enflurane and sevo?
What is the VP of des?
Why are des and sevo less potent than iso?
Des and sevo have more F and no Cl (F has lower MW than Cl), which makes it less potent
What happens to VP as T increases?
VP increases in a non-linear fashion
What does the carrier gas do?
Picks up the volatile agent and dilutes it
What gases can make up the carrier gas?
O2, N2O, or air
What are 2 components to consider in vaporizer design?
- 1) specific heat- high S.H. will slow down temp changes with vaporization
- 2) thermal conductivity- high T.C. conducts heat better
Can modern vaporizers can adjust to different T and P?
What is the major difference btw modern vaporizers and vernitrol and copper kettle vaporizers?
Modern ones can autoregulate for temp control
How do modern vaporizers regulate output? What about the old vaporizers?
- Modern- concentration calibrated (AKA variable bypass)
- Old- measured flow (manually adjust)
What is "splitting ratio"?
Modern vaporizer splits stream of gas into bypass gas (not not enter vaporizer chamber) and carrier gas (does enter vaporizer chamber) to deliver accurate vol %
What method of vaporization do the modern machines use? The old ones?
- Modern- flow over
- Old- bubble thru
What type of vaporizer uses injected method of vaporization?
How do MAC and vol % relate when using a vaporizer?
We set volume %, but must take MAC into account. For example sevo's mac = 2, so at a vol % of 1, you are at half a mac.
What factors can affect vaporizer output?
- 1) T- as temp increases so does VP (but modern vaporizers compensate for this)
- 2) carrier gas (at very high or low flow rate less anesthetic will be delivered), ok btw 250 ml/min to 15 LPM
- -identity of carrier gas
- 3) intermittent back pressure
- 4) altitude (but vap adjusts splitting ratio)
Why would giving 100% N20 as carrier gas be harmful?
N20 dissolves in the volatile anesthetic initially and leaves less carrier gas available to pick up and deliver volatile agent. This effect lasts for only 15 mins, but volatile output will be decreased by 10% for that time.
What is the "intermittent back pressure" or "pumping effect"?
Occurs with pos. pressure ventilation (spont or controlled), pressure is transmitted back to the vaporizer and drags more volatile agent with it, so more volatile agent is given than is dialed by the CRNA.
If we were giving anesthesia on the top of a mountain with decrease atm pressure with a copper kettle, how would this affect conc of volatile delivered?
- More would be delivered.
- iso makes up a larger proportion of pressure
Why is des special?
- -It must be stored in a pressurized container (makes it less volatile since its VP and BP are close to RT and atm P)
- -Needs a heated vaporizer
Why does des need a special vaporizer with a heat source ?
It has a high MAC (low potency) so you need to give a large amount, process of vaporization is cooling, so could immediately cool is there were no external heating mechanism.
Can you refill the iso vaporizer while it's on?
NO, only the special des vaporizer can be refilled while in use (closed system)
What happens if you overfill or tip over a vaporizer container?
Agent can enter the bypass chamber and more volatile will be given to the pt
Can I use sevo and iso at the same time?
NO! Only 1 volatile agent can be used at a time.
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