*Inhaled Anesthetics Part 1 (Exam III) Flashcards
What is the pharmacokinetics of Inhaled Anesthetics and the 3 components?
Uptake from alveoli into pulmonary capillary blood
- Distribution
- Metabolism
- Elimination via lungs
S3
What influences the pharmacokinetics of Inhaled Anesthetics?
- ↓ lean body mass
- ↑ fat
- ↑ Vd for drugs (especially for more fat soluble)
- ↓ clearance if pulmonary exchange is impaired
- ↑ time constraints due to lower cardiac output
S3
What is Boyle’s Law?
What application of this was mentioned in class?
- Pressure and Volume of gas are inversely proportional (at a constant temperature)
- Bellows contract thus increasing circuit pressure → gasses flow from high pressure circuit to low pressure lungs.
S4
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.
S5
What factors is diffusion dependent on?
- Partial pressure gradient of the gas
- Solubility of the gas
- Thickness of the membrane
S5
Which patients have problems with diffusion (according to Dr. Kane)?
Pediatrics born with thicker surfaces or distance
S5
What is Graham’s Law of Effusion?
Process by which molecules diffuse through pores and channels without colliding.
S6
Smaller molecules effuse faster dependent on ________.
solubility
S6
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.
CO2 mol wt 44g ; O2 mol wt 32g
S6
When PA equals ___________, then the inhaled gas concentration equals the exhaled gas concentration and the patient is unconscious.
PBrain
S7
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.
S7
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.
S7
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
S8
Which factors affect the uptake of anesthetic gas from the alveoli to the blood?
- Blood:gas partition coefficient
- Cardiac output
- A-V pressure difference
S8
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
S8
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.
S8
Gas goes from a ____ gradient to a ____ gradient in order to reach a steady state.
high; low
S8
What does PI mean?
Partial pressure of Inspired volatile gas
(or Inspired Pressure)
S10
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
S10
What does FE/FI mean?
FE/FI is the ratio of expired gas to inspired gas
(Fraction of Inspired gas)
S11
What concept is this chart conveying?
Concentration Effect: essentially, ↑concentration inspired gas = ↑PA = increased rate of diffusion
S11
What is over-pressurization?
A large increase in PI so as to force gas from PA → Pa → PBrain much faster.
S12
What would sustained delivery of
over-pressurization result in?
Overdose
S12
What gas does the second gas effect always apply to?
N₂O (nitrous oxide)
S13
What is the second gas effect as it relates to anesthesia?
- Uptake of N₂O accelerates a concurrently administered volatile gas.
S13
How does N₂O create the second gas effect?
N₂O hyper-concentrates volatiles to create a high concentration gradient by being super-diffusible.
S13
Describe what is being depicted on the graph below.
This is the concentrating effect of N₂O on Halothane.
S14
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).
S15
What specific cases are bad for the usage of N₂O?
- Ear & eye
- Open belly
- Lung
in lecture
What factors affect the magnitude of pressure N₂O would exert on a cavity that it filled?
- Partial pressure of N₂O
- Blood flow to the cavity
- Duration of N₂O administration
S15
What would nitrous inhalation in a patient with pneumothorax do?
Expand the pneumothorax
S16
What could N₂O on an intraocular case do?
- Massively increase retinal artery pressure and cause permanent vision loss.
1 hour after administering N2O
S16
Decreased __________ from hyperventilation will decrease cerebral blood flow and limit induction speed.
PaCO₂
S18
Dose dependent depressant effects of alveolar ventilation causes a ____ feedback loop
negative
S19
During spontaneous ventilation as input decreases due to ↓ventilation, volatile anesthesia is redistributed…
From tissue with high concentration (brain)
To tissue with low concentration (fat)
As brain concentration decreases ventilation increases
S19
What is the difference between Spontaneous vs Mechanical ventilation?
Patients don’t have the ability to equilibrate with mechanic ventilation so we have to alter the mechanical ventilator.
CHECK DICTATION
S19
What is the definition of solubility for anesthetic gasses?
Ratio of how inhaled gas distribution between two compartments at equilibrium
(when partial pressures are equal).
S20
If the temperature of blood increases then solubility _________.
decreases
S20