Inhaled Anesthetics Part 1 (Exam III) Flashcards
(96 cards)
What is Boyle’s Law?
What application of this was mentioned in class?
- Pressure and Volume of gas are inversely proportional
- Bellows contract thus increasing circuit pressure → gasses flow from high pressure circuit to low pressure lungs.
What is Fick’s Diffusion Law (as is pertinent to inhaled anesthetics)?
Once air molecules enter alveoli, they move around randomly and begin to diffuse into the pulmonary capillaries.
What factors is diffusion dependent on? (according to Fick’s Law)
- Partial pressure gradient of the gas
- Solubility of the gas
- Thickness of the membrane
What is Graham’s Law of Effusion?
Process by which molecules diffuse through pores and channels without colliding.
Smaller molecules effuse faster dependent on ________.
solubility
Which diffuses faster CO₂ or O₂ ? Why?
Which would you expect to diffuse faster?
CO₂ is 20x more diffusible due to solubility despite O₂ weighing less.
If you gave the same amount of CO2 and O2 to a patient, which would show up more in their blood?
The CO2 because it is 20x more soluble than O2 and likes to be in the blood.
When PA equals ________, then the inhaled gas concentration equals the exhaled gas concentration and the patient is unconscious.
PBrain
If PBrain is greater than PA then what we expect to be occurring? Why?
The patient should be waking up. This means the exhaled gas is greater than the inhaled gas and the concentration gradient is moving towards the alveoli away from the brain.
What does the following equation mean?
PA ⇌ Pa ⇌ PBrain
This is comparing the partial pressure of volatile gas in the alveoli to the arterial blood to the brain.
Where are 3 concentration gradient changes where a Delta P happens in the course of gas reception of the patient?
- Machine to alveoli
- Alveoli to Blood
- Blood to Brain
If Pi is the inspired partial pressure of a gas, is that the same as the concentration of that gas?
Yes Pi=[ ]
What input factors affect the diffusion of volatile gas from the anesthetic machine to the alveoli?
- Inspired partial pressure (Pi)
- Alveolar ventilation (RR)
- Anesthetic system re-breathing
- FRC
Which factors affect the uptake of anesthetic gas from the alveoli to the blood?
- Blood:gas partition coefficient
- Cardiac output
- A-V pressure difference
How would a low cardiac output affect the diffusion of anesthetic gas from the alveoli to the pulmonary capillary blood?
↓CO = more time to diffuse across the alveolus and pick up gas.
A high cardiac output would be too fast to pick up every molecule and be more inefficient
What factors affect the uptake of anesthetic gas from the arterial blood to the brain?
- Blood:Brain partition coefficient
- Cerebral blood flow
- A-V partial pressure difference.
Gas goes from a ____ gradient to a ____ gradient in order to reach a steady state.
high; low
What does PI mean?
Partial pressure of inspired volatile gas.
It is equal and the same as the concentration of the gas.
How can gas be “forced” to the brain quicker?
By increasing PI. This creates a higher gradient for the gas to flow from PA → Pa → PBrain
This is known as over-pressurization to achieve faster results. (like turning Sevo (MAC 1.8) on to 7 for a quick induction and then turning it back down to 1.8)
What does FE/FI mean?
FE/FI is the ratio of expired gas to inspired gas.
What concept is this chart conveying?
Concentration Effect: essentially, ↑concentration inspired gas = ↑PA = increased rate of diffusion
What is over-pressurization?
- A large increase in PI so as to force gas from PA → Pa → PBrain much faster in order to achieve its induction effect faster.
What would sustained delivery of over-pressurization result in?
Overdose, so don’t leave that sevo at 7! Drop it back down!
What gas does the second gas effect always apply to?
N₂O (nitrous oxide)
