*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
What does a low blood solubility mean for induction?
Less gas has to be dissolved = PA → Pa is rapid = rapid induction.
S20
What does a high blood solubility mean for induction?
More gas has to be dissolved = PA → Pa is slow = slow induction.
S20
What is being described in the graph below?
How quickly the inspired concentration of a gas equals the alveolar concentration of said gas.
S21
What volatile gases are intermediately soluble?
- Halothane
- Isoflurane
S21
What is the blood:gas partition coefficient of Halothane?
Halothane = 2.54 : 1
S22
What is the blood:gas partition coefficient of Isoflurane?
Isoflurane = 1.46 : 1
S22
What volatile gasses are poorly soluble (in order)?
- Desflurane
- N₂O
- Sevoflurane
S22
What is the blood:gas partition coefficient of Desflurane?
Desflurane = 0.42 : 1
S22
What is the blood:gas partition coefficient of N₂O?
Nitrous = 0.46 : 1
S22
What is the blood:gas partition coefficient of Sevoflurane?
Sevoflurane = 0.69 : 1
S22
What are the blood:gas solubilities of all the gasses we have to know for anesthesia pharm?
S22
Differentiate between Blood:Gas partition coefficient vs Fat:Blood partition coefficient (accoriding to lecture).
What is an anesthetic implication due to the difference?
Blood:Gas Coefficient = affects going to sleep
Fat: Blood Coefficient = affects waking up
You can do any combination of gases based on solubility coefficient and comorbidity.
S22
What occurs (in regards to our partial pressure gradients) during emergence from anesthesia?
Concentration gradient reverses.
PA ← Pa ← PBrain
S24
Emergence
What causes rapid washout of Inhaled Anesthetics from brain?
- High cardiac output
- Inhaled anesthetics not highly soluble in brain
Check dictation
S24
What is emergence dependent on and why?
Length of anesthetic
due to:
* PI is zero (inhaled agent is turned off)
* Muscle/fat maybe not at equilibrium
* Muscle/fat continue to take up anesthetic (helps decrease PA and PBr)
-Remember VRG…
S24
What helps decrease concentration of volatile anesthetic in PA and PBrain on emergence?
Continued uptake by Muscle/Fat if not already at equilibrium.
S24
What color coding does Isoflurane have?
Purple
S25
What color coding does Sevoflurane have?
Yellow
S25
What color coding does Desflurane have?
Blue
S25
Which anesthetic would you anticipate as having the quickest recovery?
Slowest?
Fastest recovery = Desflurane
Slowest recovery = Halothane
S26
What is 1 MAC?
Concentration at 1atm that prevents skeletal muscle movement in response to surgical stimulation in 50% of patients.
If I cut you, ur not gon’ move in 50% of the patients;
enough for others
S27
What is 1.3 MAC?
Concentration at 1atm that prevents skeletal muscle movement in response to supramaximal, painful stimulation in 99% of patients.
S28
What would ED99 be equivalent to in regards to MAC?
ED99 ≈ 1.3 MAC
S28
What is MACawake?
0.3 - 0.5 MAC: partial awakeness and responsiveness.
S28
What is MACBAR?
1.7 - 2.0 MAC
Blunts autonomic responses.
No SNS response at all, essentially an overdose.
S28
What factors are standardized MAC values based on?
30 - 55 y/o at 37°C at 1atm
REMEMBER THIS!!!!!
S28
What is the MAC of N₂O?
What does this mean?
N₂O MAC = 104%.
Can’t be used as sole anesthetic agent.
S29
What is the MAC of Halothane?
0.75%
S29
What is the MAC of Isoflurane?
1.17%
S29
What is the MAC of Desflurane?
6.6
S29
What is the MAC of Sevoflurane?
1.8%
S29
What are the two biggest factors that affect MAC?
- Body temperature
- Age
S30
At what age does MAC peak?
1 y/o
S30
How much does MAC need decrease as one gets older?
6% per decade.
S30
What is the formula to determine how much MAC to give your patient?
1.3 x MAC % of the Inhaled Agent
If pt. > 55 y/o multiple # with 6% then subtract new number with OG #
If pt. < 30 y/o multiple # with 6% then add new number with OG #
discussed in lecture; S29
What factors will increase MAC?
- Hyperthermia
- Excess Pheomelanin (redheads)
- Drug-induced ↑ catecholamines
- Hypernatremia
S31 - MEMORIZE THIS
What factors will decrease MAC?
Extensive list
Essentially anything that slows metabolism
- Hypothermia
- Pre-op meds
- Intra-op opioids (Fentany + derivatives)
- α-2 agonists (Dex, clonidine)
- Acute EtOH
- Pregnancy
- Early post-partum
- Lidocaine
- PaO₂ < 38 mmHg
- Mean BP < 40mmHg
- Cardiac Bypass
- Hyponatremia
S32
What factors does not change MAC?
- Chronic alcohol abuse
- Gender
- Duration of anesthesia
- PaCO2 15-95 mm Hg
- PaO2 > 38 mm Hg
- Blood pressure > 40 mm Hg
- Hyper/hypokalemia
- Thyroid gland dysfunction
S33 - MEMORIZE THIS
Spinal immobility is caused by 3 pathways
- Depress excitatory AMPA and NMDA (glutamate receptors)
- Enhance inhibitory glycine receptors
- Act on sodium channels
Check
S35
How does loss of consciousness occur with the use of volatile anesthetics?
- Potentiation of GABAA in the brain.
- Potentiation of glycine in the brainstem.
S36
What is Partial Pressure?
A mixture of gases in a closed container exert a pressure on the walls
S38
What is Dalton’s law?
- The sum of all partial pressures will equal the total pressure.
- Ptotal = Pgas1 + Pgas2…
S38
What is Vapor Pressure
Pressure at which vapor and liquid are at equilibrium
S39
Which of these two liquids in enclosed containers has the higher vapor pressure?
Liquid B: more evaporative.
Vapor pressure is the pressure at which vapor and liquid are at equilibirum.
S39
What is Henry’s Law?
The amount of dissolved gas in a liquid is proportional to its partial pressure above the liquid.
S40
What does Henry’s law mean in practice?
Henry’s Law is pertinent to overpressurization.
If partial pressure of a volatile doubles, then double the molecules will interact with Pa from the alveoli.
Heat will _____ vapor pressure.
increase
S41
Cold temperatures will _____ vapor pressure.
decrease.
S41
A lower vapor pressure gas is inherently more volatile. T/F ?
False. ↑vapor pressure = ↑volatility
S41
What is the vapor pressure of Halothane?
243
S41
What is the vapor pressure of Enflurane?
175
S41
What is the vapor pressure of Isoflurane?
238 torr (mmHg)
S41
What is the vapor pressure of Desflurane?
669 torr
S42
What is the vapor pressure of Sevoflurane?
157 torr (or mmHg)
S42
What do the numbers on the right, bottom area show on the monitor?
The End Tidal and Fraction of Inspiration of a volatile gas (according to lecture)?
S43
What is the variable bypass on the anesthetic machine?
A way to dilute/concentrate the amount of anesthetic gas reaching the patient.
S44
What is the splitting ratio?
How much gas is being sent into the vaporizer
S44
What is the purpose of the wicks found in the vaporizing chamber below?
The wicks increase gas-liquid interface and improve vaporization.
S45
