Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Anesthesia > Volatile Anesthetics > Flashcards

Volatile Anesthetics Flashcards

1
Q

What are the blood:gas coefficients for:

  1. Desflurane
  2. N2O
  3. Sevoflurane
  4. Isoflurane
  5. Halothane
A
  1. 0.42 (1ml of gas holds more than 1ml of blood)
  2. 0.47
  3. 0.65
  4. 1.4
  5. 2.4

1ml of blood holds 1.4x as much isoflurane as does 1ml of alveolar gas = “relatively soluble in blood”

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is a solubility or partition coefficient?

A

different physiologic mediums (mainly gas, blood, and tissue) have different capacities for carrying an anesthetic gas

difference b/w capacities of any two given mediums expressed as a ratio

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

How does anesthetic solubility effect agent equilibration b/w blood and alveolar gas?

A

a less soluble agent equalizes blood & gas partial pressures faster than a more soluble agent

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What coefficient determines speed of induction and what is the relationship b/w anesthetic solubility and induction speed?

A

Blood:Gas

less soluble = faster maximum is dissolved = faster CNS effect/induction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What 3 factors affect time needed for given type of tissue to reach anesthetic equilibrium

A

solubility
mass of tissue
perfusion rate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What partition coefficient has greatest effect on anesthetic emergence?

A

Fat:Blood > muscle:blood

Fat = large relative mass, low perfusion, anesthetics very soluble

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Is there more or less volatile anesthetic in vapor form if the vapor pressure is high?

A

More?

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What will happen when you fill a SEVO vaporizer (157mmHg) with ISO (238mmHg)

A

Higher % of ISO will be delivered

Lower vapor pressure –> lower amount of gas in vapor form –> more fresh gas flow needed

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is the second gas effect?

A

A large volume of alveolar gas absorption –> inc rate of uptake of companion gas

  • the impact that a high concentration of N2O has on the uptake of a volatile anesthetic
  • wash-in of a large volume of N2O across the alveolar membrane will reduce alveolar volume. Since the volume of the second gas has not changed, its concentration is increased. Subsequently fresh inspired gas will flow in to replace the lost volume. The net result is a higher alveolar fraction [FA] of the second gas.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the likely mechanism of N2O?

A

Antagonism of excitatory NMDA receptors

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is the effect of volatile anesthetics on CMRO2 and CBF, ICP?

A

dec CMRO2
(SEVO-ISO > DES&raquo_space;> HAL)

INC CBF, ICP
(HAL&raquo_space; DES > ISO > SEVO) from vasodilation

Mismatch = “luxury perfusion”

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What are some byproducts of volatile gases when CO2 absorbent is desiccated?

A

CO - Desflurane

Heat - Sevoflurane

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Why should total gas flow of Sevo be >2 l/min if given for prolonged periods?

A

Production of Compound A is increased

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

How can halothane, isoflurane and desflurane cause immune-mediated hepatic injury?

A

Trifluouroacetic acid byproducts - bind liver proteins –> haptens

ISO & DES very low hepatic metabolism = very rare

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What are the effects of volatile anesthetics on:

  1. Hepatic blood flow
  2. Renal blood flow
  3. Bronchi
A
  1. Dec hepatic BF (HAL - most)
  2. Dec RBF and GFR
  3. Potent bronchodilators except DES = irritant
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Describe the effects of N2O on:

  1. Cardiovascular system
  2. Pulmonary vascular resistance
  3. CMRO2
  4. CBF
  5. Muscle
  6. Renal BF
A
  1. Mildly depresses + stim SNS –> little if slight inc HR, BP, CO, SVR
  2. PVR INC
  3. CMRO2 INC
  4. CBF INC (no uncoupling)
  5. No muscle relaxation
  6. RBF dec
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Who may be at risk for neurologic injury with N2O use?

A

B12 deficiency, homocystinuria, folic acid metabolism

- oxidizes cobalt –> inactivates B12 functions (myelination)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What are the effects of N2O on a pneumothorax, tympanoplasty graft, intravitreal gas, ETT cuff?

A
  1. double size of ptx
  2. displace graft
  3. blindness w/ intravitreal gas
  4. inc pressure in ETT cuff
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

How does altitude affect DES delivery?

A

Its vaporizer delivers a constant % of gas

At high altitudes, the ambient pressure is lower = partial pressure of delivered DES will also be lower

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What variables augment the elimination of anesthetic gas?

A 
high fresh gas flows
low circuit volumes
decreased anesthetic solubility
high cerebral blood flow
increased ventilation
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What variables affect the rate of rise of FI of inhaled anesthetics?

A

fresh gas flow rate
volume of breathing circuit
gas absorption by machine/circuit

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What variables affect the rate of rise of FA of inhaled anesthetics?

A

blood:gas partition coefficient (solubility)
alveolar blood flow (cardiac output)
anesthetic partial pressure gradient between alveoli andvenous blood

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Define MAC

A

[alveolar] of an anesthetic at atmospheric pressure that prevents gross, purposeful movement in 50% of patients in response to surgical stimuli

End-tidal partial pressures ~= [alveolar]

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What do MAC and 1.3 MAC represent on a dose-response curve?

A

MAC = ED50

1.3 MAC = ED95

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What is MAC-awake?

A

0.3-0.4 MAC

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What is MAC intubation?

A

[alveolar] that would inhibit movement & coughing during intubation

> 1MAC b/w ED95 and MAC-BAR

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What is MAC-BAR?

A

[alveolar] prevents adrenergic response to skin incision

1.7-2.0x MAC

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What things increase MAC?

A
  • Hyperthermia
  • Hyperthyroidism (severe)
  • Alcoholism (chronic)***
  • Cocaine (acute intoxication)
  • Ephedrine (Based on studies in dogs with ephedrine infusions)
  • Younger age (i.e., children)***
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What decreases MAC?

A
  • Hypothermia***

* Severe hypotension (MAP

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

What factors have no effect on MAC?

A
  • Duration of anesthesia
  • Gender
  • Metabolic acid-base status
  • Hypercapnia and hypocapnia
  • Isovolemic anemia
  • Hypertension
  • Hypothyroidism
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

What is the MAC of Sevo?

A

2.0

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

What is the MAC of Halothane?

A

0.75

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

What is the MAC of Isoflurane?

A

1.2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

What is the MAC of Nitrous Oxide?

A

104

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

What is the MAC of Desflurane?

A

6.0

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

How do volatile anesthetics affect SSEPs, VEPs and MEPs?

A

INC cortical latency

dec cortical amplitude in dose dependent manner

Isoflurane&raquo_space; desflurane and sevoflurane

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

Under what circumstances is a volatile agent most damaging to EP monitoring?

A

High (>1 MAC) and changing anesthetic levels

[High] can eliminate EPs all together

50% dec in amplitude +10% inc latency is significant

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

How does N2O affect SSEPs and VEPs?

A

Profoundly depresses

39
Q

What EPs are most –> least sensitive to anesthetic effects?

A 
Most = Motor EPs
Middle = cortical EPs
Least =  brainstem auditory EPs
40
Q

What are thought to be the receptors at which volatile anesthetics produce amnesia, sedation, immobility?

A

GABA - excitatory

Lesser and significantly variable at NMDA receptors

41
Q

What is the primary difference between N2O and volatile gases in terms of receptor effects?

A

N2O = primarily NMDA

Activity assoc w/ learning, memory, pain (esp chronic)

42
Q

Describe the effects of isoflurane, sevoflurane and desflurane on MAP, SVR, HR and CO.

A

Dec MAP, SVR
Inc HR slightly (preserved baroreceptor reflex)
Preserved CO

May dec CO if LV function compromised

43
Q

What happens to HR and MAP with rapid rises in isoflurane and desflurance concentration?

A

HTN
Tachycardia

Induces sympathetic stimulation

44
Q

How do volatile anesthetics affect heart ionotropy?

A

Negative ionotropes

Dec LV contractility offset by dec after load from dec SVR

45
Q

How do volatile anesthetics affect cardiac electrophysiology (SA node, arrhythmias etc)?

A

Depress SA node activity
Prolong His-Purkinje conduction
Red VF
Prolong QTc (no reports of death however)

46
Q

How does N2O affect hemodynamics?

A

Sympathomimetic –> maintains CO with slight inc in HR, MAP

Inc pulmonary vascular resistance

Does not dec myocardial injury like other gases

47
Q

What effect do volatile anesthetics have on tidal volume and respiratory rate?

A

Dose-dependent decrease in tidal volume
INC in respiratory rate
Overall dec minute ventilation

Pulmonary stretch receptor sensitization
Inc CO2 tension enflurane >des = iso >sevo=halothane >Nitrous

48
Q

How do inhaled anesthetics affect the response to hypoxia and hypercarbia?

A

Dose-dependent depression (brainstem & carotid bodies)

49
Q

What concentration of volatile agent may attenuate hypercapnia-induced increases in ventilator drive?

A
50
Q

Where is the major site where volatile anesthetics attenuate the ventilator response to hypoxia?

A

Peripheral chemoreceptors

Halothane > enflurane> isoflurane >sevoflurane > desflurane

51
Q

Which inhaled anesthetic does not provide muscle relaxation?

A

N2O does NOT provide an muscle relaxation

52
Q

Which inhaled anestheics potentiate neuromuscular blockade and how do they do this?

A

ALL

Shift AChR from normal to desensitized –> weakens transmission
Spinal cord mediated - NMDA and glycine receptors

53
Q

What are the effects of volatile anesthetics on RBF, GFR and UOP?

A

Decrease

54
Q

What organ metabolizes methoxyflurane to an inorganic compound that causes renal failure?

A

Kidneys –> inorganic fluoride –> polyuric renal insufficiency

Propofol actually causes most cases of renal injury and failure (infusion syndrome)

55
Q

What catalyzes the breakdown of sevoflurane to compound A?

A

Base-catalyzed reaction w/ CO2 absorbents

56
Q

How does halothane cause auto-immune hepatits?

A

Dose-dependent
Metabolized –> trifluoroacylated molecules –> bind host proteins –> immunogenic complexes

Peds = 1:10,000
Adults = 1:200,000
57
Q

Describe how N2O –> reduction in DNA synthesis and megaloblastic anemia?

A

inactivation of methionine synthetase –> decreases methyltetrahydrofolate and homocysteine –> tetrahydrofolate and methionine

This –> a reduction in thymidine synthesis – a key component in DNA synthesis.

58
Q

What two clinical syndromes are characteristic of prolonged N2O exposure?

A
  1. Megaoblastic anemia (12-24hrs of 50%)

2. Subacute combined degeneration of the spinal cord (chronic daily use)

59
Q

What volatile anesthetics release inorganic fluoride when metabolized?

A

Methoxyflurane, enflurane and sevoflurane

60
Q

What factors increase production of Compound A nephrotoxicity?

A
  1. low fresh gas flows
  2. [higher] sevo
  3. higher absorbent temp
  4. absorbent dessication
61
Q

What clinically is seen in fluoride nephrotoxicity?

A

Polyuric renal insufficiency
Normal BUN
Normal Cr

62
Q

What 4 volatile anesthetic are likely to cause liver toxicity from most to least likely?

A

Halothane > enflurane > isoflurane > desflurane

63
Q

Define the concentration effect.

A

greater [inspired] of inhaled anesthetic –> more rapid equilibration between the concentrations of the inspired and alveolar gases

–> upward shift of the uptake curve (alveolar fraction [FA] / inspired fraction [Fi] over time).

64
Q

What are the two components of the concentration effect?

A

The concentrating effect - effect of lung volume on alveolar gas concentrations

  • Diffusion of anesthetic from the alveoli to the blood reduces the alveolar volume –> remaining anesthetic more concentrated
  • alveolar gas has a high fraction of anesthetic = more volume change, and a greater effect on overall gas concentrations.

Augmented tracheal inflow - gas absorbed from alveolar space is replaced by fresh gas that flows in from the proximal lung regions

  • actual inspired volume of gas&raquo_space;> if there is a [high] of anesthetic agent present due to this replacement
  • since the new gas will contain anesthetic agent at the inspired concentration [Fi], alveolar gas will have a higher [FA] than would be predicted by simply removing the absorbed gas from the alveolar gas.
65
Q

What is the clinical significance of the concentration effect?

A

only clinically significant when nitrous oxide is being administered in very high concentrations - it affects its own uptake

The concentrations of other modern volatile agents are not high enough for the concentration effect to play an important role in their uptake. This difference is why the increase in [FA]/[Fi] is more rapid for nitrous oxide than desflurane, even though they have similar solubility in blood.

66
Q

Name five properties that make nitrous oxide uniquely different to other inhaled anesthetics.

A
  1. not a halogenated hydrocarbon
  2. gas at ambient temperature
  3. MAC >100 = much less potent, NOT used as the sole anesthetic
  4. Much less soluble than all other inhaled anesthetics, except desflurane.
  5. only inhaled agent that provides analgesia
  6. only inhaled agent that does not cause significant uterine relaxation
  7. inactivates methionine synthase, which regulates vitamin B12 and folate metabolism and converts homocysteine to methionine –> worsen a pre-existing B12 deficiency
  8. may inc risk of PONV
67
Q

Name three phenomena that occur with the onset or discontinuation of nitrous oxide.

A
  1. rate of rise of inc in the [alveolar] of inhaled anesthetic relative to the inspired concentration (PA/Pi) plotted against time is steep during first few minutes
  2. A concentration effect with high inspired concentrations of N2O (e.g. 70%) - Initial uptake of N2O is so rapid –> concentrate the gases that remain in the alveoli = shrink the total lung volume = second gas effect when used with another gas (sevo)
  3. outpouring of large volumes of N2O –> diffusion hypoxia by directly oxygen in the alveoli. First 5-10 minutes after nitrous oxide is discontinued.
68
Q

Name 6 situations in which nitrous oxide is contraindicated

A
  1. venous air embolism and pneumothorax
  2. intracranial air (pneumocephalus following dural closure)
  3. pulmonary air cysts
  4. intraocular air or injected gas bubbles (i.e., SF6)
  5. tympanic membrane grafting
  6. obstructed bowel with air-fluid levels
  7. air embolism risk (e.g. posterior fossa craniotomy, laparoscopic surgery).
69
Q

How does a liquid differ from a gas in regards to compressibility?

A

liquid is not very compressible

70
Q

How is a gas different from a vapor?

A

A vapor may go from liquid to gas and can exist alongside its corresponding liquid

A vapor is a gas, but a gas is not necessarily a vapor
- some gases cannot be liquefied at room temperature; (nitrogen and oxygen)

A vapor is a gas below its critical temperature

71
Q

How does temperature affect equilibrium vapor pressure of a liquid?

A

Vapor pressure is directly proportional to temperature

72
Q

If the number of gas molecules and temperature are held constant, and the volume increases, what happens to the pressure?

A

PV = nRT

If the number of gas molecules and the temperature are held constant, and the pressure increased, then the volume must decrease by an inverse proportion

73
Q

Why does an E cylinder of N2O contain liquid and gas, whereas an E cylinder of oxygen contains only gas?

A

The critical temperature O2 = -116°C = gas at room temperature.

N2O critical temperature = 36.5°C
N2O may be liquefied if temperature is kept below 36.5°C = E-cylinder contains both liquid and gas forms

74
Q

What is a vapor’s critical temperature?

A

temperature above which further increasing the pressure is not effective in turning the vapor back into a liquid

75
Q

What does the vapor pressure associated with a liquid volatile agent depend on?

A

the agent itself and temperature

76
Q

Why does desflurane require its own special vaporizer?

A

its boiling point, which is near room temperature, is much lower than the other agents.

77
Q

How does barometric pressure affect boiling point of a liquid?

A

A decrease in barometric pressure will cause the liquid to boil at a lower temperature.

This is why liquids boil at lower temperatures at high altitudes, creating more vapor

78
Q

What is Volume %?

A

Vol % = (partial pressure due to vapor/ total ambient pressure) x 100 %

represents a relative ratio of gas molecules in a mixture, whereas partial pressure represents an absolute value measured in mmHg

Clinically, anesthetic potency and uptake are directly related to partial pressure, but only indirectly related to Vol %

79
Q

What is the definition of latent heat of vaporization?

A

energy required to transform a liquid –> vapor phase

80
Q

Why do vaporizers use materials of high thermal capacity?

A

allow for heat transfer to the liquid in order to compensate for the heat loss that occurs with vaporization (keep the liquid from cooling)

81
Q

What 2 basic types of vaporizers are there?

A

variable bypass and measured flow

82
Q

What is the splitting ratio in a variable bypass vaporizer?

A

The ratio of flow diverted into vaporizing chamber to become saturated with agent to the flow bypassing the chamber to dilute the saturated flow

controlled by adjusting the setting of the vaporizer’s concentration control dial to regulate the relative flow rates through the bypass and vaporizing chambers

83
Q

How do vaporizers automatically compensate for changes in ambient temperature?

A

increasing the amount of bypass flow (increasing the splitting ratio) as temperature increases

  1. gas-filled bellows that expands with rising temperatures
  2. temperature-sensitive bypass valves
  3. bimetallic strips made from 2 metals with different coefficients of expansion that bend according to temperature and regulate flow
84
Q

How can the hourly consumption of liquid volatile agent be approximated?

A

Liquid consumption in mL = 3 x Vaporizer setting in Vol % x FGF in L/min

85
Q

Does the output of a vaporizer, when expressed in terms of the partial pressure of inhaled anesthetics, change with changes in atmospheric pressure?

A

No

saturated vapor pressure (SVP) and fraction of gas diverted to vaporization chamber are NOT affected by the ambient pressure

output Vol % of a conventional variable-bypass vaporizer calibrated at sea level will INCREASE at high altitudes and the [anesthetic agent] will exceed the [dialed-in]

86
Q

How does adding air or N2O to O2 in the carrier gas affect vaporizer output in a vaporizer calibrated using 100% O2? Why?

A

Vaporizers calibrated using 100% O2 decrease their output slightly at low flow rates when air or N2O is added

Oxygen has a greater viscosity than air and N2O

87
Q

How does the vapor pressure of desflurane compare to sevoflurane or isoflurane?

A

DES = high vapor pressure (681 mmHg) and is virtually boiling at room temperature

SEVO and ISO are much lower at room temperature (160 and 240 mmHg respectively) resulting in much less agent in the vapor form

88
Q

What parameters are controlled in the Tec 6 vaporizer to compensate for desflurane’s unique properties?

A

electrically heated, pressurized device specifically designed to deliver desflurane over a wide range of environmental conditions

89
Q

How does the Tec 6 vaporizer adjust for changes in fresh gas flow rates?

A

increases its internal working pressure in proportion to an increased fresh gas flow while keeping a constant 39°C temperature

90
Q

Does fresh gas flow pass through the desflurane reservoir in a Tec 6 Vaporizer?

A

NO

A valve to the reservoir opens and allows pressurized vapor to leave

Using pressure as a surrogate measure of fresh gas flow rates, an electronic feedback system gathers pressure information from both limbs of this system in order to inject the proper concentration of DES into the fresh gas flow

91
Q

Can the Tec 6 vaporizer be used during its warm-up period?

A

NO

internal shutoff valve remains closed to prevent use of the vaporizer

92
Q

Why is the risk of anesthetic overdose decreased in the Tec 6 vaporizer when vaporizer is tilted?

A

An output valve prevents emptying of gas when powered off.

If the Tec 6 vaporizer is tilted for 10 seconds while the dial is ON and it is in operational mode, vapor delivery will be stopped, as indicated by the flashing NO OUTPUT light and auditory alarm.

93
Q

Does the difference in viscosity between O2 and N2O significantly affect the delivery of desflurane delivered by the Tec 6?

A

low viscosity of N2O, the desflurane output DECREASES when N2O is added to oxygen (O2), but remains within 20% of the dial setting. Therefore, the differences are not significant and should have little effect in clinical practice.

94
Q

What effect does high altitude have on the Tec 6 output of desflurane?

A

DES vaporizer dialed to 6% @ sea level and @ 10,000 feet (500 torr), the partial pressure of desflurane delivered to the patient is:

  1. 06 x 760 mm Hg = 45.6 mmHg DES @ sea level
  2. 06 x 500 mm Hg = 30 mmHg DES @ 10000 feet

Compensation is required: (Dial setting at sea level) x (760/ambient pressure torr) = the required dial setting at 10000 feet

At 10,000 feet the ambient pressure is 500 torr. 6% x (760/500) = 9% required on the dial to achieve the desired partial pressure

Setting a DES dial that has been calibrated at sea level to 6% –> lighter anesthesia at high altitude than it does at sea level

Anesthesia (25 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions