Vapor Pressure & SVP
What is the term that describes the maximum vapor pressure a liquid can exert at a given temperature.
What is Saturated Vapor Pressure (SVP)?
This represents the concentration preventing movement in 50% of patients.
What is MAC (Minimum Alveolar Concentration)?
The process of vaporization causes this.
What is cooling?
The splitting ratio in a variable bypass vaporizer is determined by these three factors.
What are the anesthetic agent, temperature, and desired concentration?
A Sevo vaporizer accidentally filled with Iso will deliver concentrations that are:
What is higher than expected?
Calculate PMAC for a volatile agent with a MAC of 2%.
0.02×760=15.2 mmHg
As temperature increases, this property increases.
What is SVP?
This measurement better reflects anesthetic concentration in the CNS.
What is PMAC (Minimum Alveolar Pressure)?
Energy required to convert liquid into vapor.
What is latent heat of vaporization?
Fresh gas flow is divided between these two pathways.
What are the bypass chamber and vaporizing chamber?
The first action if a vaporizer is suspected to be misfilled.
What is empty the vaporizer,, remove it from service, label it as misfiled, and return it to the manufacturer?
Isoflurane SVP = 238 mmHg.
Calculate SVC.
238/760×100 = 31%
The boiling point occurs when SVP equals this.
What is atmospheric pressure?
Among Iso, Sevo, and Des, this is the most potent agent.
What is isoflurane?
Property that acts as the vaporizer's "thermal battery."
What is specific heat?
These structures increase surface area inside the vaporizing chamber.
What are baffles and wicks?
An Iso vaporizer accidentally filled with Sevo will deliver concentrations that are:
What is lower than expected?
A Sevo vaporizer is filled with Iso and set to 2%.
Calculate output concentration.
0.02 x (238/160) x 100
≈ 2.975% or 3%
Among Isoflurane, Sevoflurane, and Desflurane, this agent has the highest SVP.
What is Desflurane?
The PMAC of Sevoflurane.
What is 16 mmHg?
Which property allows environmental heat to rapidly replenish the cooling liquid? Acts as the vaporizer's "express highway."
What is thermal conductivity?
As dial setting increases, the splitting ratio does this.
What is decreases?
If tilted, the vaporizer should be flushed with this before returning to use.
What is high-flow oxygen?
Use a calibrated agent analyzer to confirm the efficacy of the flush before returning to clinical use(end tidal agent concentration should decrease to zero).
A Sevo vaporizer is filled with Iso and set to 2%.
Output concentration is approximately 3%.
What MAC equivalent of Iso is delivered?
Iso MAC = 1.15%
3/1.15 ≈ 2.6 MAC
As altitude increases, atmospheric pressure decreases, causing this change in boiling point.
What is boiling point decreases?
The relationship between MAC and potency.
What is inverse? (Lower MAC = higher potency)
The best vaporizer construction material because of its high specific heat and thermal conductivity.
What is copper?
At a 1% setting, Isoflurane requires a larger bypass ratio than Sevo because of this property.
What is higher saturated vapor concentration (SVC)?
DAILY DOUBLE
Modern vaporizer temperature compensation is not instantaneous. Approximately how long does the Dräger 19.n vaporizer require to compensate for a 1°C temperature change?
A Dräger 19.n vaporizer experiences a 2°C drop in temperature. Approximately how long will it take to fully compensate?
What is 6 minutes?
What is 12 minutes?
DAILY DOUBLE:
A vaporizer without temperature compensation is used continuously for an hour.
Describe the chain of events that leads to a decrease in anesthetic output.
Vaporization → heat loss → temperature falls → SVP falls → less vapor produced → anesthetic output decreases.