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*Barash > Volatile Anesthetics > Flashcards

Volatile Anesthetics Flashcards

1
Q

The CNS partial pressure of inhaled anesthetics equals what pressure, which in turn equals alveolar pressure if cardiopulmonary function is normal.

A

Arterial partial pressure

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2
Q

What determine the speed of induction of the inhaled anesthetics?

A

Concentration of blood:gas solubility

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3
Q

What determines the rate of elimination of inhaled anesthetics?

A

Solubility

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4
Q

What is the most potent volatile anesthetics?
What is the least soluble?
What is the least irritating?

A

Isofourane
Desflurane
Sevoflurane

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5
Q

This volatile anesthetics can double or triple its size in 10 to 30 minutes

A

Nitrous oxide

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6
Q

Is the alveolar concentration of an inhaled anesthetic at one atmosphere that can prevent movement in response to a surgical stimulus in 50% of patients.

A

Minimum alveolar concentration

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7
Q

Concentrations of inhaled anesthetics that provide loss of awareness and recall are about?

A

0.4 to 0.5 MAC

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8
Q

MAC decreases approximately how many percent per decade?

A

6%

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9
Q

True or false

Volatile anesthetics decrease ventilatory response to hypercarbia and hypoxia and INCREASE respiratory rate.

A

True

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10
Q

CO2 absorbente degrade, sevoflurane, isoflurane and desflurane to CO when the normal water content of the absorbent (13 to 15%) is markedly decreased to?

A

< 5%

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11
Q

Who was the first to examine the pharmacokinetics of inhaled anesthetics in a systematic fashion?

A

Kety

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12
Q

What is the lowering of one concentration in one compartment by delivery into another compartment?

A

Reistribution

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13
Q

What are the only 2 true gases?

A
  1. N2O

2. Xenon

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14
Q

Are volatile anesthetics ionized or non ionized?

A

Nonionized

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15
Q

Potent volatile anesthetics are LIQUIDS at ambient temperature and pressure except for?

A

Desflurane

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16
Q

At equilibrium, the pressure exerted by molecular collisions of the gas against the container walls is referred to as?

A

Vapor pressure

As long as any liquid remains in the container, the vapor pressure is independent of the volume of that liquid.

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17
Q

Is the temperature at which its vapor pressure exceeds atmospheric pressure in an open container.

A

Boiling point

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18
Q

This volatile anesthetic is bottled in a special container because of its boiling point.

What is its boiling point?

A

Desflurane

23.5 C

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19
Q

For any mixture of gases in a closed container, each gas exerts a pressure proportional to?

A

Fractional mass called partial pressure

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20
Q

Refers to the pressure of gas in the gas phase in equilibrium with the liquid,

A

Partial pressure

Gas equilibriate based on PARTIAL PRESSURES, not concentrations.

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21
Q

Is the tendency of gas to equilibrate with a solution.

A

Solubility

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22
Q

Read

A

For any gas in equilibrium with a liquid, a certain volume of that gas dissolves in a given volume of liquid.

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23
Q

The concentration of any one gas in a mixture of gases in solution depends on two factors

A
  1. Partial pressure
  2. Solubility

Anesthetic gases administered via the lungs diffuse into blood until the partial pressures in alveoli and blood are equal.

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24
Q

Read

A

The partial pressure of a gas in solution represents the pressure that the gas in equilibrium with the liquid would have if a gas phase existed in contact with the liquid phase.

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25
Q

The concentration of anesthetic in target tissue depend on 2 factors

A
  1. Partial pressure at equilibrium

2. Target tissue solubility

26
Q

Summary

A
  1. Inhaled anesthetics equilibrate based on their partial pressures in each tissue, not based on their concentrations.
  2. The partial pressure of a gas in solution is defined by the partial pressure in the gas phase with which it is in equilibrium. When there is no gas phase the partial pressure reflects a force to move out of solution.
  3. The concentration of anesthetic in a tissue depends on its partial pressure and the tissue solubility of the anesthetic.
27
Q

Partial pressure is expressed in mmHg or Torr or kilopascals

1 Torr = 1 mmHg

A

Fractional volume = partial pressure / atmospheric pressure

28
Q

The fractional concentration of anesthetic leaving the circuit is designated as?

The fractional concentration of anesthetic present in the alveoli is called?

A

Fraction inspired (Fi)

Fraction alveolar (Fa)

29
Q

Vessel rich group organs

A
  1. Brain
  2. Heart
  3. Kidney
  4. Liver
  5. GIT
  6. Glandular tissue
30
Q

The CNS tissues of the VRG are referred to as?

A

Tissue of desired effect

31
Q

The tissues of the muscle and fat are called?

A

Tissues of accumulation

32
Q

Is the ratio of dissolved gas (by volume) in two-tissue compartment at equilibrium

A

Partition coefficient

33
Q

Read

A 
FA = PA (FA = PA / P barometric)
PA = P blood = P CNS

F FGO is the fraction of inspired anesthetics in the gas leaving the fresh gas outlet (vaporizer setting)

The time constant is simply the volume or capacity of the circuit divided by FGF

Example, if the bag, tubing, absorbent canister, and piping comprise 8L, and the FGF is 2L, the time constant is 8/2 = 4.

One of the characteristics of first order kinetics is that 95% of maximum is reached AFTER THREE TIME CONSTANTS. (3x4 = 12 mins).

34
Q

What is the most important factor in incresing FI?

A

High flow FGF

35
Q

There are two ways to speed the equilibration of FA with FI, that is to decrease time constant.

A
  1. Increase minute ventilation

2. Decrease FRC

36
Q

What is the reason that pediatric inductions by spontaneous breathing of inhaled anesthetics are so much quicker than adults is?

A

Low FRC relative to VA of children makes for a low time constant

37
Q

Read

A

The more soluble the inhaled anesthetic, the larger the capacity of the blood and tissues for that anesthetic, and the longer it takes to saturate at any given delivery rate.

38
Q

Less soluble to more soluble inhaled anesthetics (5)

A 
Nitrous oxide
Desflurane
Sevoflurane
Isoflurane
Halothane
39
Q

What is the most important factor in the rate of rise of FA/FI?

A

Uptake of anesthetic from the alveoli into the bloodstream

Since uptake is proportional to tissue solubility, the less soluble the anesthetic, the lesser its uptake and the faster it reaches equilibrium.

40
Q

Read (Fick equation)

A

The greater the value of VB, the greater the uptake from alveoli to blood, and the slower the rise in FA/FI.

41
Q

The muscle partition coefficient is approximately double that for the VRG except for what inhaled anesthetic?

A

Nitrous oxide

42
Q

Perfusion of

  1. VRG
  2. Muscle
A
  1. 75 mL/min/100 g of tissue

2. 3 mL/min/100 g of tissue

43
Q

Fat equilibrates far more slowly with the blood and does NOT play a significant role in determining speed of induction. After long anesthetic exposure, the high saturation of fatty tissue may play a role in delaying emergence. How long is this.

What inhaled anesthetic is an exception as its partition coefficient is similar in each tissue.

A

> 4 hours

Nitrous oxide

44
Q

Loss of inhaled anesthetic via the skin is greatest with what anesthetic?

A

N2O

45
Q

Recovery from anesthesia depends on 3 factors

A
  1. Solubility
  2. Cardiac output
  3. Minute ventilation
46
Q

Read (emergence)

A

The more soluble anesthetics are eliminated more slowly than less soluble agents

47
Q 
Halogenated methyl ether
NON-flammable
MOST POTENT
Has greatest physical stability (can be stored for 5 years)
Gold standard anesthetic
CORONARY STEAL
A

Isoflurane

48
Q

Fluorinated methyl ether
Differs my isoflurane by 1 atom (fluorine atom substitutes chlorine atom)
Decreases blood tissue solubility (x5 more potent than isoflurane)
Makes hepatitis a rare occurence
MOST PUNGENT
Degrades to form CO
LOWEST BLOOD GAS SOLUBILITY
Requires kess downward titration to achieve rapid emergence
Ideal for OBESE
TACHYCARDIA and HYPERTENSION

A

Deflurane

49
Q 
Completely fluorinated
2nd blood gas solubility to desflurane
Ideal for facemask induction
Does not form antibodies to cause hepatitis
Can cause high heat and fire
A

Sevoflurane

50
Q

Quick onset and offset
Not a trigger for malignant hyperthermia
NMDA receptor inhibition

A

Xenon

51
Q

Insoluble in blood
At room temperature it is a gas (boiling point = -88.48C)
Pressure: 745 psi
Reliable indicator of volume : cylinder weight
Side effect: PONV, Vit B12 inactivation, expansion of air filled spaces, disrupts embryonic devt

A

Nitrous oxide

52
Q

Concentrations of inhaled anesthetics that provide loss of self-awareness and recall

A

0.4 to 0.5 MAC

53
Q

Is the alveolar concentration of anesthetic at which a patient opens his or her eyes to command

What is the value?

A

MAC-awake

0.15 to 0.5 MAC

54
Q

Is the alveolar concentration of anesthetic that blunts adrenergic responses to noxious stimuli

What is the value?

A

MAC-BAR

50% higher than standard MAC

55
Q

Factors that increase MAC (4)

A
  1. MAOIs, dextroamphetamine, cocaine, ephedrine, levodopa
  2. Hyperthermia
  3. CHRONIC alcoholism
  4. HYPERnatremia
56
Q

Factors that does not alter MAC

A
  1. Duration of adminstration
  2. Gender
  3. Type of surg stimulation
  4. Thyroid function
  5. Hypo hypercarbia
  6. Metabolic alkalosis
  7. Mg
57
Q

How much decrease in MAC at the age of 40 to 80

How about age 1 to 40 years old?

A

22%

27%

58
Q

Desflurane and sevoflurane both influence CBF in a manner similar to isoflurane, with minimal changes in CBF at concentrations less than how much MAC?

A

1.5

59
Q

The increase in CBF with increasing anesthetic dose occurs despite decreases in CMRO2. This phenomenon is referred to as?

A

Uncoupling

60
Q

Sevoflurane preserves autoregulation up to approximately how much MAC?

A

1 MAC

*Barash (16 decks)

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