ƛ * Q * (A-v) Solubility * CO * difference in alveolar/venous partial pressures
Solubility's effect on the rate of rise of FA/FI curve:
Less soluble = faster rate of rise
The use of high FD to increase the speed of FA=FI equilibration
Effect of CO on induction speed:
Increasing Cardiac Output = decreased speed of induction
Tissue uptake equation:
Uptake = tissue/blood coefficient * flow * (a-t)
The coefficient that most influences FA/FI rise:
The coefficient that most influences the FA/FI tail:
Minimum alveolar concentration; ED50 of inhaled anesthetics. The concentration that will produce absence of movement in 50% of the population.
↑ ventilation will have more of an effect on FA/FI curve for this type of agent:
Highly soluble agent
Effect of both ↑ ventilation and ↑ CO:
↑ ventilation has more effect (to speed induction) than ↑ CO does (to slow it)
If only one lung is intubated, what is the effect on the rise in FA and rise in Pa?
FA rises faster than if the ETT was in the trachea However, loss of uptake from unventilated lung leads to overall depressed ↑ in Pa
Higher blood-gas coefficient means:
Agent is more soluble More agent in blood = less in alveoli/brain
Type of gas that will washout fastest:
N2O is ____x as soluble as nitrogen:
Places that N2O can diffuse into during surgery:
1. ETT cuff 2. Bowel obstruction 3. Pneumothorax/pneumocephalus 4. Inner ear 5. Ophtho procedures using gas bubbles 6. Air embolus
Another name for blood-gas partition coefficient:
Oswaldt Solubility Coefficient
Brain-level activity of a highly vs. minimally soluble IA:
Highly soluble: low brain activity Minimally soluble: high brain activity
Effect of solubility on emergence
Less soluble = faster induction/emergence More soluble = slower induction/emergence
Five partial pressure gradients between vaporizer and end-target tissue:
Vaporizer and inflow, Inflow and circuit, Circuit and alveoli, Alveoli and blood, Blood and tissues
Impact of HCT on B/G coefficient:
↓ HCT = ↓ B/G coefficient Dropping HCT from 21 --> 43 drops B/G coefficient by 20% D/t less binding sites in the blood
FA vs. FI:
FA = alveolar concentration FI = inspired concentration
FD = FI when:
High flow rate with no re-breathing
Make these changes to ventilation to ↑ uptake:
↓ TV, ↑ rate
PA of volatile anesthetic is determined by (4):
1. PI (inhaled partial pressure) 2. Alveolar ventilation 3. Breathing circuit 4. FRC
Normal alveolar ventilation, minute ventilation and deadspace:
Alveolar Ventilation = 4 L/min Minute ventilation = 6 L/min Dead space = 2L/min
Solubility's effect on the rate at which FA approaches FI:
Less soluble agents will reach equilibrium faster They have a faster rate of rise
Describe the FA/FI curve:
First rise: VRG uptake First knee: VRG at equilibrium Second rise: MG uptake Second knee: MG at equilibrium Third rise: FG/VPG uptake (very slow)
With lower solubility (
1. Gas phase 2. Blood phase
What determines which direction the gas will move
How long does it take the fat compartment to reach equilibrium?
Rate of induction/emergence of an anemic patient
Faster induction and emergence
What determines how quickly FA= FI ?
Solubility - less soluble = faster equilibrium
Partial Pressure that represents anesthetic going to the brain
FA (fraction of alveolar concentration)
What do we as anesthetists control
FI (fraction of inspired concentration) - the % dials
What is out overall goal with induction
Get the FA/FI ratio to 1:1 quickly - the faster to equilibrium - the faster the induction
PA (alveolar pressure ) is used to estimate 3 things
1. Depth of anesthesia 2. Recovery from anesthesia 3. Anesthetic Potency (dose) or MAC (ED50)
Exhaled gas readings during induction and emergence. During induction readings will be ____________ than what is set on the dial d/t ________________. During emergence the readings will be higher than what is set on the dial d/t ___________.
Induction - lower; Uptake occurring in the tissues Emergence - higher; tissue giving up previously absorbed IA
What has a faster induction, iso or des?
des- it is less soluble and has a faster rate of rise and therefore reaches equilibrium much faster.
Why does nitrous have a faster rate of rise than desflurane?
Despite des being less soluble nitrous will rise faster because of the concentration effect.
What opposes the effect of ventilation?
A increase in CO will cause a ____________ in the FA/FI ratio. this means that the patient will be induced ___________.
A decrease in CO will cause a ____________ in the FA/FI ratio. this means that the patient will be induced ___________.
Changes in CO will have a greater effect on the ____________ soluble agents. Why?
More soluble. They have more time to equilibrate with the passing blood.
Changes in ventilation will have greater effects on ______________ agents. Why?
More Soluble. Alveolar pressure will build up much faster in both, but the rate of rise will increase more for the highly soluble agents.