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Anesthesia Pharmacology > Lecture 11 (Exam 3 Inhaled Anesthetics Part 1) > Flashcards

Lecture 11 (Exam 3 Inhaled Anesthetics Part 1) Flashcards

1
Q

Pharmacokinetics describes these four things in inhaled anesthetics.

A
  1. Uptake from the alveoli into the pulmonary capillary blood.
  2. Distribution
  3. Metabolism
  4. Elimination via Lungs
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2
Q

The pharmacokinetics of inhaled anesthetics are influenced by ________.

A

Aging

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3
Q

What factors does aging contribute to the pharmacokinetics of inhaled anesthetics?

A

Decreased body mass

Increase fat mass, increase Vd for lipid-soluble drugs

Decrease clearance if the pulmonary exchange is impaired (COPD, atelectasis)

Increase time constraints d/t lower cardiac output

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4
Q

Boyle’s Law states that at a constant temperature, pressure and volume of a gas are __________ ___________.

As PPV begins, bellows _____. This will cause pressure to ______ within circuit. Anesthetic gases will flow from ____ to _____

A

Inversely proportional.

Application:
As positive pressure ventilation begins, the bellows contract. This will cause pressure to increase within the ventilator and circuit resulting in anesthetic gases flowing from high pressure to low pressure (lungs).

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5
Q

What is Fick’s law of diffusion?

A

It describes the rate at which molecules move from an area of high concentration to an area of low concentration.

Application:
Once the molecules get to the alveoli, they move around randomly and begin to diffuse into the pulmonary capillary.

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6
Q

What three things does diffusion depend on?

A
  1. Partial pressure gradient of the gas (high to low)
  2. Solubility of the gas (diffusion)
  3. Thickness of the membrane
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7
Q

According to Graham’s Law of Effusion,____ molecules effuse faster dependent on _________.

A

Smaller
Solubility** (Not just based on size alone)

Example:
Carbon dioxide, molecular wt 44 g
Oxygen, molecular wt 32 g
Carbon dioxide is 20x more diffusible because it is more soluble than O2.

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8
Q

An inhaled anesthetic will travel from the alveolus to the pulmonary artery and to the ___________ in one or two circulation times to exert its effect.

A

brain

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9
Q

What is alveolar pressure an indicator of?

How is alveolar pressure measured?

A

Depth of anesthesia (“Is patient asleep enough?”)
Recovery of anesthesia (“Is the patient waking up?”)

Pulmonary alveolar pressure can be measured through end-tidal gas.

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10
Q

If the amount of anesthetic gas is greater in the alveolus (PA) than in the brain (PBr) what does that mean?

If the amount of anesthetic gas is greater in the PBr than in PA, what does that mean?

A

The patient is still awake, there is still room in the brain for anesthetic gas.

Gas is leaving from the brain (vessel-rich) to the alveolus where the patient will eventually wake up.

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11
Q

What are the 3 partial pressure gradients that affect the induction process?

A
  1. Anesthetic machine to alveoli
  2. Alveoli to blood
  3. Arterial blood to the brain
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12
Q

What is a partition coefficient?

A

The partition coefficient refers to the relative solubility of the anesthetic gas between two compartments.

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13
Q

What four factors will affect the input of the volatile anesthetic from the anesthetic machine to the alveoli?

A
  1. Inspired partial pressure
  2. Alveolar ventilation
  3. FRC
  4. Anesthetic breathing system (Is there a lot of breathing?)
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14
Q

What 3 factors will affect the uptake of volatile anesthetics from the alveoli to the blood?

A
  1. Blood: gas partition coefficient
  2. Cardiac output
  3. Alveolar-to-Venous partial pressure differences
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15
Q

What 3 factors will affect the uptake of volatile anesthetics from the arterial blood to the brain?

A
  1. Brain: blood partition coefficient
  2. Cerebral blood flow (dependent on CO)
  3. Aterial-to-Venous partial pressure difference
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16
Q

What factor contributes to how rapidly PA (pressure of the alveolus) approaches PI (Pressure of Inspired Volatile)?

A

Concentration Effect (concentration gradient)

6% desflurane will get a patient sedated faster than 1% desflurane.

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17
Q

How would you offset a slow induction from highly soluble volatiles?

A

Over pressurization, a large increase in inspired pressure (PI).

Get the patient asleep in a couple of breaths, but sustained delivery will result in an overdose.

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18
Q

1 _________ breath of high concentration of Sevoflurane (7%) will result in loss of eyelash reflex (stage 2).

A

vital capacity

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19
Q

The second gas effect is the use of high-volume gas (________) concurrently with a volatile (sevoflurane, isoflurane, desflurane).

A

Nitrous (N2O)

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20
Q

Why is Nitrous always used in the second gas effect?

A

Nitrous creates a concentration effect.

The high volume of N2O uptake into the pulmonary capillary (very diffusable) will increase the concentration of the 2nd gas (ie: desflurane). This will increase the uptake of 2nd gas due to the gradient.

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21
Q

Nitrous oxide likes to diffuse into ___________ cavities.

A

air-filed cavities (lungs, bowels, ear canals)

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22
Q

What are some procedures where you want to avoid using nitrous oxide?

A

Open belly (compliant space)
Ear Cases (non-compliant space)
Eye Cases (non-compliant space)

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23
Q

What happens if you give N2O to patients with a pneumothorax?

A

It will increase the size of the pneumothorax by 250% when compared to giving supplemental oxygen.

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24
Q

If nitrous oxide was administered during intraocular retinal repair, what will happen?

A

The patient will have retinal artery vision loss within one hour.

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25
Q

By ________ alveolar ventilation, you can increase the speed of induction.

A

increasing
(Increasing respiration rate from 10 bpm to 20 bpm).

This will work to an extent..

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26
Q

Hyperventilation will cause a decrease in __________ which will____ cerebral blood flow (vasoconstriction) and limit the speed of induction.

A

PaCO2

decrease

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27
Q

Differentiate between spontaneous ventilation and mechanical ventilation.

A

Spontaneous ventilation has a dose-dependent depressant effect on alveolar ventilation (negative feedback loop). As input decreases d/t decreased ventilation the volatile redistributes from tissue w/ high concentration (brain) to tissues w/ low concentration (fat). As brain concentration decreases, ventilation increases.

When mechanical ventilation, the body is not able to provide a negative feedback loop. The ventilator will continue to administer molecules at a set rate.

28
Q

Solubility is defined as a ________ of how the inhaled anesthetic distributes between 2 compartments at _________ when partial pressures are equal.

A

Solubility is defined as a ratio of how the inhaled anesthetic distributes between 2 compartments at equilibrium when partial pressures are equal.

29
Q

Solubility is temperature dependent. If the temperature of the blood increases, solubility _________.

A

Decreases
The volatile anesthetic agent does not want to stay in the blood, it will want to go into the brain. Faster induction

30
Q

If blood solubility is high, a large amount of volatile anesthetics must be dissolved. How will this affect induction?

A

The anesthetic agent wants to stay in the blood and induction is prolonged.

31
Q

Which one has the lowest solubility?

A. Desflurane
B. Sevoflurane
C. Isoflurane

A

Desflurane will have the lowest solubility followed by Sevo and then Iso.

This means that people will go to sleep and wake up faster from desflurane.

32
Q

Halothane has a Blood: Gas Partition Coefficient of___. What does that mean?

A

When the relative ratio is the same (when solubility equals out). There is 2.54 times more Halothane in the blood than in the gas compartment. This means that halothane is VERY soluble, it likes to stay in the blood. The blood will hold a lot of halothane. Slow induction and slow emergence.

33
Q

What is the Blood: Gas Partition Coefficient of Desflurane?

A

0.42

This means that desflurane is not very soluble and does not want to stay in the blood. Fast induction, fast emergence.

34
Q

What is the Blood: Gas Partition Coefficient of Halothane?

A

2.54

35
Q

What is the Blood: Gas Partition Coefficient of Isoflurane?

A

1.46

36
Q

What is the Blood: Gas Partition Coefficient of Nitrous Oxide?

A

0.46

37
Q

What is the Blood: Gas Partition Coefficient of Sevoflurane?

A

0.69

sexy sevo

38
Q

Emergence depends on the rate of decrease in ______.
This process begins when the inspired partial pressure of volatile gas is _______ mmHg

A

Pbr
0 mmHg

39
Q

How _________ the gas is determines how soon the gas will be turned off for emergence.

A

soluble.

Less soluble turn gas (desflurane) will be turned off toward the end of surgery. More soluble gas (isoflurane) will be turned off sooner.

40
Q

What are the colors associated with the following volatile gasses?
Isoflurane:
Sevoflurane:
Desflurane:

A

Isoflurane: Purple
Sevoflurane: Yellow
Desflurane: Blue

41
Q

What is the definition of MAC?

A

The minimum alveolar concentration (MAC) is the concentration at 1 atm that prevents skeletal muscle movement in response to supramaximal, painful stimulation in 50% of patients.

42
Q

The MAC required to prevent skeletal muscle movement in response to supramaximal, painful stimulation in 99% of patients will be ________.

A

1.3 MAC

43
Q

What is the value for MACawake

A

0.3 - 0.5 MAC

Patient will be able to respond to touch and sound, there will be protective airway reflexes.

44
Q

What is the value for MACbar

A

1.7 - 2.0 MAC

BAR- Blunt Autonomic (Adrenergic) Responses.

At MACbar there will be no SNS response to intubation.

45
Q

Based on 30-55 y/o average, 37 degrees, C; 760 mmHg (1 atm) what is the MAC value of Nitrous?

A

104%

Unable to give a MAC of nitrous unless you are in a hyperbaric chamber. Nitrous is never given alone as a general anesthetic. Nitrous is used as a supplement (second gas effect).

46
Q

Based on 30-55 y/o average, 37 degrees, C; 760 mmHg (1 atm) what is the MAC value of Halothane?

A

0.75%

47
Q

Based on 30-55 y/o average, 37 degrees, C; 760 mmHg (1 atm) what is the MAC value of Isoflurane?

A

1.17%

48
Q

Based on 30-55 y/o average, 37 degrees, C; 760 mmHg (1 atm) what is the MAC value of Desflurane?

A

6.6%

49
Q

Based on 30-55 y/o average, 37 degrees, C; 760 mmHg (1 atm) what is the MAC value of Sevoflurane?

A

1.8%

50
Q

What are the two biggest factors that alter MAC?

A

Body Temperature
Age- 6% per decade (under 30, above 50)

51
Q

Factors that increase MAC. 4

A

Hyperthermia
Excess pheomelanin production (red-heads)
Drug-induced increase in catecholamine levels
Hypernatremia

52
Q

Factors that decrease MAC. 10

A

Hypothermia
Pre-op Meds (BZD), intraop opioids
Alpha-2 agonist (precedex, clonidine)
Acute EtOH ingestion
Pregnancy
Post partum (12-72 hours)
Lidocaine
PaO2 < 38 mmHg
Mean BP < 40 mmHg
Cardiopulmonary Bypass
Hyponatremia

53
Q

Factors that do not affect MAC. 8

A

Chronic EtOH abuse
Gender
Duration of anesthesia
PaCO2 15-95 mmHg
PaO2 > 38 mmHg
Hyper/hypokalemia
Thyroid gland dysfunction

54
Q

Anesthesia affects spinal immobility by depressing excitatory _________ and _________ receptors.

Spinal immobility is also affected by enhancing inhibitory ________ and acts on sodium channels to block the release of __________.

A

AMPA
NMDA
glutamate receptors

Spinal immobility is also affected by enhancing inhibitory glycine and acts on sodium channels to block the release of glutamate.

55
Q

There will be a loss of consciousness by the inhibitory transmission of GABA in the _________ and especially the _______.

A

Brain and RAS

There will be potentiation of glycine activation in the brainstem.

56
Q

What is the pressure that would be exerted by one of the gases in a mixture if it occupied the same volume on its own?

A

Partial Pressure

Sum of the partial pressures will equal total pressure (Dalton’s Law)

57
Q

The pressure at which the vapor and liquid are at equilibrium.

A

Vapor Pressure

58
Q

What is Henry’s Law?

A

The amount of dissolved gas in a liquid is proportional to its partial pressure above the liquid.

The more dissolved gas that is in the liquid, the more partial pressure in the vaporizer. -This is how over-pressurizing works.

59
Q

________ increases vapor pressure.
________ decreases vapor pressure.

A

Heat increases vapor pressure.
Cold decreases vapor pressure.

60
Q

The greater the vapor pressure the more likely to ______ and be considered more _________.

A

The greater the vapor pressure the more likely to evaporate and be considered more volatile.

Ie: Desflurane

61
Q

What is the vapor pressure of Halothane?

A

243 torr

62
Q

What is the vapor pressure of Isoflurane?

A

238 torr

63
Q

What is the vapor pressure of Desflurane?

A

669 torr

64
Q

What is the vapor pressure of Sevoflurane?

A

157 torr

65
Q

What is one way the vaporizer dilutes saturated gas

A

Splitting Ratio

• fresh gas flow comes in vaporizer. control dial by changes in opening to let some fresh gas go past the vaporizer “by pass pathway and goes back to tubing and to patient

66
Q

What kind of vaporizer increases the gas-liquid interface and improves the efficiency of vaporization?

___ improve vaporization

A

Flow-over vaporizer
Wicks

67
Q

Magnitude of pressure exerted by nitrous depends on 3 factors.

A

PP of nitrous
Blood flow to cavity
Duration of nitrous administration

Anesthesia Pharmacology (20 decks)

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