Exam 3 Flashcards
Boyle’s law states that given a constant temperature, pressure and volume of gas are…
inversely proportional
Applying Boyle’s law:
1. As PPV begins, the bellows ______
2. _____ increases within ventilator and circuit
3. Anesthetic gases flow from __ pressure to __ pressure, aka into the _____
- contract
- pressure
- High to low, the lungs
What influences the pharmacokinetics of volatile anesthetics?
(old) Aging!
So…
* decreased lean body mass
* increased fat
* increased Vd for drugs (especially for more fat soluble)
*Decreased clearance if pulmonary exhange is impaired
*Increased time constraints due to lower CO
What is the main effector site for volatiles?
The brain!
Diffusion depends on 3 things. List them
- Partial pressure gradient of the gas
- Solubility of the gas (diffusion)
- Thickness of the membrane
Fick’s diffusion law
Once the molecules get to the alveoli, they move around randomly and begin to diffuse into the pulmonary capillary
Graham’s law of effusion states that smaller molecules effuse ____ dependent on _____
fast, solubility (diffusion)
Although Oxygen is smaller than Carbon dioxide, carbon dioxide is 20x more diffusible. Why?
Carbon dioxide is very soluble!
This is the process by which molecules diffuse through pores and channels without colliding
Effusion
Alveolar pressure is an indicator of these two things
-Depth of anesthesia
-Recovery from anesthesia
What four things are included in the partial pressure gradients between the anesthetic machine to alveoli (aka input)
-Inspired partial pressure
-Alveolar ventilation
-Anesthetic breathing system (is there a lot of rebreathing?)
-FRC
What three things are included in the partial pressure gradients between the alveoli to blood?
-Blood: gas partition coefficent
-Cardiac output
-A-v partial pressure difference
What 3 things are included in the partial pressure gradients between the arterial blood to brain?
-Brain: blood partition coefficent
-Cerebral blood flow
-a-v partial pressure difference
Which two partial pressure gradients make up “uptake”?
Alveoli to blood
Arterial blood to brain
The impact of PI on the rate & rise of PA is known as the…
concentration effect!
The higher the PI of a volatile, the more rapidly ____ approaches ____
PA approaches PI
The impact of the inhaled concentration of an anesthetic on the rate at which the alveolar concentration increased toward the inspired (FE/FI) is known as the
concentration effect
Explain over pressurization..
What happens with sustained delivery?
Explain the second gas effect
The uptake of a high volume gas (N2O) accelerates a concurrently administered companion gas (volatile)
Explain what is happening here
This is the second gas effect! Halothane with 70% nitrous approaches FE/FI faster than halothane with 10% nitrous
How much and how fast does nitrous diffuse into air-filled cavities?
Up to 10L in the first 10-15 minutes
1 hour of nitrous for retinal repair results in
-Increased intraocular pressure during retinal repair
-Retinal artery vision loss
Explain how respiratory rate impacts PA and PI
Increased RR speeds PA towards PI and therefore speeds the induction of anesthesia
How does decreased PACO2 impact the speed of induction
Decreased PACO2 decreases CBF and limits speed of induction
What is solubility?
A ratio of how the inhaled anesthetic distributes between two compartments at equilibrium (when partial pressures are equal)
How does temperature impact solubulity?
If the temperature of blood increases, solubility decreases
How does solubility of an anesthetic impact induction/emergence?
The more soluble, the more it likes to stay in blood. Slower to sleep, slower to wake
Blood:gas partition coefficent of halothane
2.54
Blood:gas partition coefficent of enflurane
1.90
Blood:gas partition coefficent of isoflurane
1.46
Blood:gas partition coefficent of nitrous oxide
0.46
Blood:gas partition coefficent of desflurane
0.42
Blood:gas partition coefficent of sevoflurane
0.69
Which three volatiles are intermediately soluble
Halothane, enflurane, isofulrane
Which three volatiles are poorly soluble
Nitrous oxide, desflurane, sevoflurane
What is 1 MAC?
The concentration at 1 atm that prevents skeletal muscle movement in response to supramaximal, painful stimulation in 50% of patients
1.3 MAC prevents ___% of patients from moving
99%
At what MAC will patients wake?
0.3-0.5 MAC
What is MACBAR
What is the # for this?
1.7-2.0 MAC
What patient population are MAC values based on?
30-55 years old (at 37 degrees and 1 atm)
MAC % Nitrous oxide
104
MAC % Halothane
0.75
MAC % enflurane
1.63
MAC % isoflurane
1.17
MAC % desflurane
6.6
MAC % sevoflurane
1.8
What are the two biggest factors that alter MAC?
-Body temperature
-Age
At what age does MAC peak?
1 year old
Explain how MAC changes per decade..
MAC goes up or down 6% per decade
Example:
10 years old - up 12%
20 years old - up 6%
30-55 - no change
60 - down 6%
70 - down 12%
80 - down 18%
90 - down 24%
4 things that cause increases in MAC?
-Hyperthermia
-Excess pheomelanin production (redheads)
-Drug-induced increase in catecholamine levels
-Hypernatremia
11 things that cause decreases in MAC
Hyponatremia, hypothermia, hypoxia (PAO2 <38), hypotension (<40 mmHg)
Pregnancy, postpartum
Lidocaine
Cardio pulm. Bypass
Acute alcohol
Alpha 2 agonist
Synergistic meds
8 things that do NOT change MAC
How do volatiles cause spinal immbolity (3 ways)?
-Depress excitatory AMPA and NMDA
-Enhance inhibitory glycine receptors
-Acts on sodium channels (blocks presynaptic release of glutamate)
How do volatiles cause loss of consciousness?
-GABA
-Potentiation of glycine activation in the brainstem
-NO effect of volatiles on AMPA, NMDA, or kainate
Daltons law
The sum of the partial pressures equals the total pressure
P Total = P gas 1 + P gas 2 + P gas 3
The pressure at which vapor and liquid are at equilibrium
Vapor pressure
aka evaporation = condensation
How does heat impact vapor pressure?
Heat increases vapor pressure
This is because it is evaporating quicker
How does cooling impact vapor pressure?
Cold decreases vapor pressure
The higher the vapor pressure, the more likely to ____
Evaporate!
Considered more volatile!
Desflurane has a high vapor pressure
Vapor pressure of halothane
243
Vapor pressure of enflurane
175
Vapor pressure of isoflurane
238
Vapor pressure of desflurane
669
Almost at sea level vapor pressure, vaporizes quicker
Vapor pressure of sevoflurane
157
How to get volumes %
Partial pressure / total pressure
What do vaporizers do?
Change liquid to vapor
Explain variable bypass
Explain flow-over
3 types of gas delivery systems
-Rebreathing (Bain)
-Non-breathing (self-inflating BVM)
-Circle systems (our machines!)
BVM is not a great way to give volatiles
A non-rebreathing system must have a bag that….
self-inflates
The circle systems contain a ____ ____ while the Bain and BVM do NOT
CO2 absorbent!
In high flow anesthesia, fresh gas flow exceeds..
Minute ventilation
2 big uses for high flow fresh gas flow
-Denitrogenate patient
-Build up O2 reservoir
Also speeds up changes in anesthetic
Cons of high flow anesthesia
-Wasteful
-Cools/dries delivered volume
Pros of high flow anesthesia
-Allows you to make rapid changes in anesthetic
-Prevents rebreathing
Pros of low flow inhalation anesthesia
-Low cost
-Less cooling/drying
Cons of low flow inhalation anesthesia
-VERY slow changes in anesthetic
-Concern with compound A production?
The price of anesthetics depends on these 3 things
-Cost of liquid/mL
-Volume % of anesthetic delivered (potency)
-FGF rate
How do volatiles relax airway smooth muscle?
What does this require your patient to have?
-Block voltage gated Calcium channels
-Deplete Ca++ in SR
Requires: an intact epithelium!
Which is better at causing bronchodilation: sevo or iso?
SEVO!
This anesthetic may worsen bronchospasm in smokers due to pungency/irritation
Desflurane
This volatile is best for kids. Why?
Sevo!
Least irritating to airwats and better at causing bronchodilation
Does nitrous oxide have a relaxant effect on skeletal muscles?
NO
How do volatiles impact skeletal muscle relaxation?
They have a dose dependent impact on skeletal muscle relaxation mediated via the spinal cord
How do volatiles potentiate NMBDs (both depolarizing and non-depolarizing)?
-nAch receptors at NMJ
-Enhance glycine at spinal cord
