Inhaled Anesthetics Part 1 (Exam III) Flashcards
What is Boyle’s Law?
What application of this was mentioned in class?
- At Constant temperature, 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?
- 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, depends on solubility)
Smaller molecules effuse faster dependent on ________.
solubility
Which diffuses faster CO₂ or O₂ ? Why?
CO₂ is 20x more diffusible due to solubility despite O₂ weighing less.
If PBrain is greater than PA then what we expect to be occurring?
This means 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.
What input factors affect the diffusion of volatile gas from the anesthetic machine to the alveoli?
- Inspired partial pressure
- Alveolar ventilation
- 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
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 is the concentration effect?
Higher the PI ⇒ PA reaches PI quicker
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 = quicker rate of ↑PA
What is over-pressurization?
- A large increase in PI to offset slow induction from highly soluble volatiles.
What would sustained delivery of over-pressurization result in?
Overdose
What gas does the second gas effect always apply to?
N₂O (nitrous oxide)
What is the second gas effect as it relates to anesthesia?
- Uptake of N₂O accelerates a concurrently administered volatile gas.
How does N₂O create the second gas effect?
Rapid N₂O uptake hyper-concentrates second gas to create a high concentration gradient and increase uptake of second gas
Describe what is being depicted on the graph below.
- This is the second gas effect of N₂O on halothane. Leads to quicker increase in halothane alveolar concentrations.
What cases would nitrous oxide not be utilized in?
Why?
- Cases with an air-filled cavity
- N₂O will diffuse into the cavity and fill it. (extent of damage dependent on the compliance of the cavity).
What specific cases are bad for the usage of N₂O?
- Ear & eye
- Open belly (stomach, intestines)
- Lung
What factors affect the degree of pressure N₂O would exert on a cavity that it filled?
- Partial pressure of N₂O
- Blood flow to the cavity
- Duration of N₂O administration
What would nitrous inhalation in a patient with pneumothorax do?
Expand the pneumothorax
What could N₂O on an intraocular case do?
- Massively increase retinal artery pressure and cause permanent vision loss.
Decreased ______ from hyperventilation will decrease cerebral blood flow and limit induction speed.
PaCO₂
Describe the negative feedback cycle of volatile depressant effects
↑RR ⇒ quicker to brain ⇒ depressant effects ⇒ ↓RR ⇒ slower to brain ⇒ brain wakes up ⇒ ↑RR ⇒ REPEAT
What is the definition of solubility for anesthetic gasses?
Ratio of how inhaled gas distribute between two compartments at equilibrium (when partial pressures are equal).
If the temperature of blood increases then solubility ______.
decreases
hyperthermia ⇒ ↓Solubility