5: Inhalation Anesthetics 1 Flashcards by Bianca Zayas

Most modern inhalational anesthetics are _____, not _____.

vapor, gas

How well did you know this?

Not at all

Perfectly

When does gas exist in a gaseous form?

At room temp and at sea level

How well did you know this?

Not at all

Perfectly

When does a vapor exist in a liquid form?

At room temp and at sea level

How well did you know this?

Not at all

Perfectly

Most inhalants we use are _____.

vapors

How well did you know this?

Not at all

Perfectly

What is the critical temperature?

Temp at and above which a vapor cannot be liquified, no matter how much pressure is applied

How well did you know this?

Not at all

Perfectly

A vapor can be liquefied _____ the critical temp when enough _____ is applied.

below, pressure

How well did you know this?

Not at all

Perfectly

What is the critical temp of isoflurane? Nitrous oxide?

Iso = ~200ºC

N₂O = ~36.4ºC

How well did you know this?

Not at all

Perfectly

What is the only gas that is routinely used?

Nitrous oxide

How well did you know this?

Not at all

Perfectly

Maximal [] of a vapor is determined by saturated _____ _____.

vapor pressure

How well did you know this?

Not at all

Perfectly

What is needed for delivery of a vapor?

vaporizer

How well did you know this?

Not at all

Perfectly

What is saturated vapor pressure?

Max [] of molecules in the vapor phase that exists for a given liquid at a given temp; it is specific for each agent.

How well did you know this?

Not at all

Perfectly

Saturated vapor pressure depends only on _____.

temperature

How well did you know this?

Not at all

Perfectly

What is the saturated vapor pressure of sevoflurane?

What is its max [] at sea level?

SVP = 157 mmHg

Max [] = 21%

How well did you know this?

Not at all

Perfectly

What is the saturated vapor pressure of halothane?

What is its max [] at sea level?

SVP = 243 mmHg

Max [] = 32%

How well did you know this?

Not at all

Perfectly

What is the saturated vapor pressure of isoflurane?

What is its max [] at sea level?

SVP = 236 mmHg

Max [] = 31%

How well did you know this?

Not at all

Perfectly

What is the saturated vapor pressure of desflurane?

What is its max [] at sea level?

SVP = 664 mmHg

Max [] = 87%

How well did you know this?

Not at all

Perfectly

What is the saturated vapor pressure of nitrous oxide?

What is its max [] at sea level?

SVP = 38,000

Max [] = 100%

How well did you know this?

Not at all

Perfectly

What is the formula for max [] at sea level?

Max [] = (SVP/barometric P) * 100%

How well did you know this?

Not at all

Perfectly

How did the Morton Etherizer (1846) work?

Piece of gauze was soaked in liquid ether and placed in the chamber, liquid starts to turn to gas

How well did you know this?

Not at all

Perfectly

What is the [] of iso in the vaporizing chamber of the vaporizer?

31%

How well did you know this?

Not at all

Perfectly

What is the Minimum Alveolar Concentration (MAC)?

Alveolar [] at which 50% of animals do not move in response to a noxious stimulus (EX: clamping base of tail or on the toe).

How well did you know this?

Not at all

Perfectly

T/F: A noxious stimulus for an animal when determining MAC can be making an incision.

False

How well did you know this?

Not at all

Perfectly

How is MAC determined (6 steps)?

An individual is anesthetized with the study drug
The end tidal [] is measured and kept constant for at least 15 min
A supramaximal noxious stimulus is applied
If “no purposeful movement”, then the [] is decreased and kept constant for another 15 min
Give the stimulus again, and if movement is seen, then the [] is increased
[] value between response and no response = MAC

How well did you know this?

Not at all

Perfectly

T/F: MAC does not vary much between spp

True

How well did you know this?

Not at all

Perfectly

At steady state, P\_\_\_\_\_ inhalant = P\_\_\_\_\_ inhalant

P_alveolar, P_brain

What are advantages of MAC?

1. Does not vary much between spp 2. At steady state, P_alveolar inhalant = P_brain inhalant

What are 3 disadvantages of MAC?

1. MAC determination is quantal - animal is either anesthetized or not 2. MAC is determined on a population level only 3. MAC definition depends on the end-point measurement (purposeful movement)

What is MAC for iso? What is the oil:gas PC?

MAC = 1.3% Oil:gas PC = 98

What is the MAC for sevo? Oil:gas PC?

MAC = 2.4% Oil:gas PC = 55

What is the MAC for desflurane? Oil:gas PC?

MAC = 7.2% Oil:gas PC = 18.7

What is the MAC for nitrous oxide? Oil:gas PC?

MAC = 188% Oil:gas PC = 1.4

What does a high oil:gas PC mean?

Drug is more fat-soluble, and therefore more potent

What gas is the most potent and why?

Isoflurane; has the highest oil:gas PC and the lowest MAC

What is surgical MAC?

[] needed for 95% of patients not to move = 1.3-1.5x MAC

What is surgical MAC of iso?

1.95%

What is surgical MAC of sevo?

3.6%

What is surgical MAC of desflurane?

10.8%

Why is there no surgical MAC for nitrous oxide?

It is not possible to give normal MAC (188%), so not possible to give 1.5x MAC because you can only give 100% of a gas; If you have 188% N₂O you would kill your patient every time.

What is the effect of other concurrent drugs on MAC? Give some examples.

They can decrease it; Ace = decreases by up to 40% Dexmedetomidine/opioids = decreases by 30-50% N₂O = decreases by 25-30%

What are the effects of temperature on MAC?

Hyperthermia increases it to a point; Hypothermia decreases it

What is the effect of pregnancy on MAC?

It decreases it

What is the effect of age on MAC?

It decreases it as age increases

What is the effect of thyroid function on MAC?

Hyperthyroidism increases MAC

Partial pressure of a drug in the _____ determines the partial pressure of the drug in the _____ and \_\_\_\_\_.

alveoli, blood, brain

What are the steps of uptake and distribution of a drug/inhalant?

1. Patient awake, vaporizer turned on 2. Anesthetic delivered into trachea and lungs 3. High [] of agent enters alveoli 4. Agent diffuses across alveolar cell membrane --\> blood 5. [] of agent in blood increases 6. Agent enters brain due to high lipid solubility and high blood flow to the brain 7. Patient anesthetized

When does anesthetic pressure in the alveoli first increase?

When the vaporizer is turned on

The higher the _____ of anesthetic, the _____ the induction.

uptake, induction

Inhalant uptake is affected by the agent \_\_\_\_\_.

solubility

What does a blood:gas ratio of 0.5 mean?

Anesthetic is half as soluble in blood as in gas

What does a blood:gas of 2.0 mean?

Anesthetic is twice as soluble in blood as in gas

The _____ the solubility in blood, the _____ the agent is taken up by pumonary circulation, the _____ the induction.

higher, more, slower

What is the B:G of halothane?

2.4

What is the B:G of iso?

1.4

What is the B:G of sevo?

0.65

What is the B:G of nitrous oxide?

0.47

What is the B:G of desflurane?

0.42

What is the speed of induction and recovery of common inhalants, from slowest to fastest?

Halothane \< Iso \< Sevo \< Nitrous oxide \< Desflurane

Rate of change at any time is proportional to the \_\_\_\_\_.

quantity at that time

When does equilibrium occur?

When input = output

How is time constant calculated and what does it mean?

= volume / flow Describes speed at which a system can respond to change

What is this?

Wash-in curve

What is this?

Wash-out curve

Your anesthesia machine has a rebreathing circuit with a 5 L volume. If your oxygen flow rate is set to 1 L/min and iso is set at 2%, how long will it take to accumulate 2% iso in the breathing circuit?

TC = volume/flow TC = 5 L / 1 L/min = 5 min Need 5 TC to reach new [] so 5 min x 5 = **25 min**

What is the Meyer-Overton rule?

Potency is related to oil solubility, so the lipid bilayer must be the site of action; BUT not all lipid soluble drugs are general anesthetics

What is the membrane protein theory?

Anesthetics bind proteins and modulate their functions; Inhibitory vs. excitatory

What receptor are anesthetics thought to bind to?

GABA - potentiates effect of GABA to increase flow of Cl ## Footnote **\*This is a hypothesis, we are not 100% sure\***

Where are anesthetics thought to work to produce unconsiousness?

Cerebral cortex

Where are anesthetics thought to work to produce analgesia?

Supra-spinal, dorsal horn

Where are anesthetics thought to work to produce amnesia?

Hippocampus, amygdala

Where are anesthetics thought to work to produce immobility?

Spinal cord

What is the most important route of elimination?

via the lungs

How is consciousness regained when an anesthetic is eliminated?

Regained as P_brain anesthetic decreases

Factors that speed _____ also speed elimination.

induction

What type of inhalants will get eliminated faster?

Those with a low B:G coefficient (EX: Desflurane)

What % of halothane is metabolized by the liver?

25%

What % of iso is metabolized by the liver?

0.2%

What % of sevo is metabolized by the liver?

2-5%

What % of desflurane is metabolized by the liver?

0.02%

What % of nitrous oxide is metabolized by the liver?

0.004%

In order from best to worst, what are the anesthetics that can be used in patients with decreased liver function?

Nitrous oxide \> Desflurane \> Iso \> Sevo \> Halothane