Anesthesiology Lecture 5 Pharmacology Of Inhalant Anesthetic Agents

Front 1

What are 4 things to consider when selecting a drug?

Back 1

1) Half life
2) Duration of effect
3) Route of administration
4) Distribution

Front 2

Inhalant anesthetics exist as a ______, but are administered as a ______.

Back 2

Exist as a LIQUID, administered as a VAPOR

Front 3

What are 5 terms that describe the properties of an inhalant anesthetic?

Back 3

1) Boiling point
2) Vapor pressure
3) Blood/gas coefficient (lambda)
4) Oil/gas coefficient
5) Minimal alveolar concentration (MAC)

Front 4

What is the one inhalant anesthetic that doesn't exist as a liquid at room temperature?

Back 4

Desflurane (boiling point= 23.5 C)

Front 5

What term describes an agent's volatility?

Back 5

Vapor pressure

Front 6

What property of an inhalant anesthetic determines the type of vaporizer used?

Back 6

Vapor pressure

Front 7

What property of an inhalant determines the maximum amount of anesthetic that can be delivered?

Back 7

Vapor pressure

Front 8

What inhalant has the most vapor pressure?

Back 8

Desflurane=700 mmHg
-Isoflurane and halothane are about 240 mmHg

Front 9

What's the equation to determine the maximum concentration of an inhalant anesthetic?

Back 9

(Vapor pressure/atmospheric pressure) x 100
e.g. 238/760 x100=31% (isoflurane)

Front 10

What does it mean that desflurane has a maximum concentration of 92%?

Back 10

Means it's a very volatile anesthetic

Front 11

What does blood/gas solubility give an indication of? (2)

Back 11

-The body's ability to "store" the drug and how effectively those depots compete with the brain for it
-indicator of speed of induction & recovery & transition b/w planes
-indication of body's capacity to "release" the drug during recovery

Front 12

Why do lipid soluble inhalants anesthetic have a longer recovery time?

Back 12

More widely distributed and stores will hold more anesthetic agent

Front 13

What determines how long the recovery of an inhalant anesthetic is going to take?

Back 13

Blood/gas solubility - if body can't store very much agent, then blood and brain concentration decreases quickly after stopping administration

Front 14

Put the inhalant anesthetics in order from lowest blood/gas solubility to highest.

Back 14

Nitrous oxide
Desflurane>NO>Sevoflurane> isoflurane> halothane > methoxyflurane

Front 15

What is the oil/gas solubility an indicator of? Why?

Back 15

Potency
-olive oil is used to determine lipid solubility, an indication of ease of penetration into the brain

Front 16

What does a higher oil/gas solubility mean?

Back 16

Higher the solubility, greater the penetration and thus analgesia obtained w/ equal doses

Front 17

Rank the potency of the 6 inhalant anesthetics.

Back 17

Methoxyflurane > halothane> isoflurane> sevoflurane> desflurane> NO

Front 18

Minimum alveolar concentration allows quantification of ______ and _________.

Back 18

quantification of dose
Comparison of agents

Front 19

What is the minimum alveolar concentration?

Back 19

Point where 50% of patients move in response to a painful stimulus (determined w/ tail clamp in many species)

Front 20

What are 3 ways the MAC can be increased?

Back 20

1) Hyperthermia
2) Hypernatremia
3) Drugs causing CNS stimulation

Front 21

What are 8 ways the MAC is decreased?

Back 21

1) Drugs causing CNS depression
-e.g. analgesics, sedatives
2) Pregnancy
3) Hypoxemia (PaO2<40 torr)
4) Hypercarbia (PaCO2>90 torr)
5) Hypothermia
6) Hypotension (Mean BP <50 mmHg)
7) Increasing adult age
8) Hyponatremia

Front 22

Does duration of anesthesia affect the MAC?

Back 22

No, as long as normothermic

Front 23

Does hypertension affect MAC? Hypotension?

Back 23

Hypotension: Yes
Hypertension: No

Front 24

Why isn't NO used as a sole agent under any conditions?

Back 24

because the minimum alveolar concentration is > 188 (isoflurane is 1.3-1.5%)

Front 25

Where does metabolism of inhalant anesthetics occur in the body?

Back 25

Primarily in liver, also lung, kidney & GI tract

Front 26

What 3 systems are depressed by inhalation agents?

Back 26

1) CNS
2) Respiratory
-Initially tidal volume, then rate, can vary by agent
3) Cardiovascular system

Front 27

What aspects of the cardiovascular system are affected by inhalation agents?

Back 27

Decreased CO, SV, HR, peripheral vascular resistance

Front 28

Inhalation agents decrease renal ________.

Back 28

Blood flow

Front 29

How is the liver affected by inhalation agents? Why?

Back 29

Hepatocellular injury may occur
-decreased blood flow & oxygen delivery or by direct injury (halothane)

Front 30

What animal is methoxyflurane cleared for use in?

Back 30

Dogs
-No longer manufactured in US

Front 31

Describe the potency, solubility and volatility of methoxyflurane.

Back 31

Very potent, highly soluble, not very volatile

Front 32

Methoxyflurane is a ______ dependent respiratory depressant.

Back 32

Dose dependent

Front 33

True or false. Methoxyflurane does not provide very good analgesia.

Back 33

False, very good analgesia

Front 34

True or false. Methoxyflurane is arrhythmogenic.

Back 34

False, not as arrhythmogenic

Front 35

True or false. Methoxyflurane provides good muscle relaxation.

Back 35

True

Front 36

Why is methoxyflurane the most nephrotoxic agent?

Back 36

Production of fluoride and oxalate production

Front 37

Methoxyflurane can cause severe _______ disease.

Back 37

Liver

Front 38

What is the induction, recovery and transition b/w planes like with methoxyflurane?

Back 38

Slow induction, recovery and transition b/w planes

Front 39

Is methoxyflurane a good choice for mask induction?

Back 39

No, poor choice

Front 40

Is methoxyflurane a good choice for animals with prexisting liver or renal disease?

Back 40

No, poor choice

Front 41

Methoxyflurane should be induced at ___-____% in small animals and maintained at ____-____%.

Back 41

Induce: 2-3%
Maintain: .2-1%

Front 42

Halothane is cleared for use in what animals?

Back 42

Dogs, cats, horses

Front 43

Is halothane available in the US?

Back 43

No, recently discontinued

Front 44

Describe the potency, solubility and volatility of halothane.

Back 44

Potent, insoluble, volatile

Front 45

True or false. Halothane is a dose dependent respiratory depressant.

Back 45

True

Front 46

What are the effects of halothane on the cardiovascular system?

Back 46

-more severe cardiovascular effect
-arrhythmogenic

Front 47

Does halothane provide muscle relaxation?

Back 47

Yes, moderate muscle relaxation

Front 48

What are 2 possible side effects of halothane?

Back 48

1) Malignant hyperthermia
2) Severe liver disease

Front 49

What is halothane a good choice for?

Back 49

Mask Induction

Front 50

What are 3 situations where you don't want to use halothane?

Back 50

Lesser choice for animals w/ prexisting liver disease, trauma, or when multiple anesthesia episodes are anticipated

Front 51

Describe the induction, recovery and transition b/w planes.

Back 51

Quick induction, recovery & transition b/w planes

Front 52

You want to induce a small animal with ____-____% of halothane and _____-____% in large animals.

Back 52

SA: 2.5-3%
LA: 4-5%

Front 53

What animals is isoflurane cleared for use in?

Back 53

Dogs, cats, horses

Front 54

Describe the potency, solubility and volatility of isoflurane.

Back 54

Less potent, insoluble, and volatile

Front 55

Describe the respiratory depression of isoflurane.

Back 55

Causes more severe respiratory depression

Front 56

Describe the cardiovascular effects of isoflurane.

Back 56

Less severe cardiovascular effects

Front 57

Is isoflurane or halothane more arrhythmogenic?

Back 57

Halothane is more arrhythmogenic

Front 58

Describe the muscle relaxation properties of isoflurane.

Back 58

Adequate muscle relaxation

Front 59

True or false. Isoflurane causes liver disease.

Back 59

False. Isoflurane doesn't cause liver or renal disease

Front 60

When is isoflurane a good choice for an anesthetic?

Back 60

Good for animals with liver or renal disease, trauma
Good choice for mask induction

Front 61

Describe the induction, recovery and transition b/w planes.

Back 61

Quick induction, recovery, and transition b/w planes

Front 62

What level do you want to induce a small animal at with isoflurane? LA?

Back 62

SA: 2-3%
LA: 4-5%

Front 63

What level do you want to maintain a small animal at? LA?

Back 63

SA: 1.5-2.5%
LA: 2-3%

Front 64

Describe the recovery from isoflurane.

Back 64

Quick, abrupt recovery
-additinoal sedative almost always given to adult horses at extubation

Front 65

Sevoflurane is cleared for use in what animals?

Back 65

Dogs, horses

Front 66

Describe the potency, solubility and volatility of sevoflurane.

Back 66

Less potent, very insoluble, less volatile

Front 67

Describe the respiratory depression of sevoflurane.

Back 67

More severe respiratory depressant

Front 68

The cardiovascular effects of sevoflurane are very similar to ______.

Back 68

Isoflurane

Front 69

Describe the muscle relaxation of sevoflurane.

Back 69

Adequate

Front 70

Does sevoflurane cause liver or renal disease?

Back 70

No

Front 71

What species is desflurane cleared to use in?

Back 71

None, not cleared for vet species

Front 72

Describe the potency, solubility and volatility of desflurane.

Back 72

Least potent, very insoluble, very volatile

Front 73

Desflurane causes respiratory depression similar to ______.

Back 73

Isoflurane

Front 74

The respiratory depression of desflurane is similar to that of ______.

Back 74

Isoflurane

Front 75

Describe the cardiovascular effects of desflurane.

Back 75

Similar to isoflurane

Front 76

Describe the muscle relaxation of desflurane.

Back 76

Adequate

Front 77

Does desflurane cause liver or renal disease?

Back 77

No, preserves hepatic & renal blood flow

Front 78

Why does desflurane require a very specialized vaporizer?

Back 78

Very stable compound

Front 79

Describe the induction, recovery and transition b/w planes when using desflurane.

Back 79

Very quick induction, recovery and transition

Front 80

When is desflurane an excellent choice for an anesthetic agent?

Back 80

Mask induction
Very long cases

Front 81

Is desflurane a good choice for animals with prexisting liver or renal disease?

Back 81

yes

Front 82

What level do you want to use to induce small animals with desflurane? LA?

Back 82

SA: 10-12%
LA:12-18%

Front 83

What level do you want to maintain SAs with desflurane? LAs?

Back 83

SA: 8-10%
LA: 8-20%

Front 84

Describe the recovery of desflurane.

Back 84

Abrupt recovery

Front 85

Nitrous oxide produces _______ and mild analgesia in animals.

Back 85

Mild cortical depression

Front 86

Describe the cardiovascular effects of nitrous oxide.

Back 86

Very minimal

Front 87

Nitrous oxide is a stable compound that is not ______.

Back 87

Metabolized

Front 88

Is nitrous oxide toxic to the liver or kidneys?

Back 88

No

Front 89

Describe the muscle relaxation of nitrous oxide?

Back 89

NO muscle relaxation

Front 90

Nitrous oxide will accumulate in what organs?

Back 90

Closed viscus
-e.g. pneumothorax, gastric dilatation-volvulus, GI obstruction, rumen, large colon)

Front 91

What do we use nitrous oxide for in anesthesiology?

Back 91

Used to supplement anesthesia by allowing a decrease in primary agent concentration
-speeds up induction

Front 92

Nitrous oxide can speed up induction through the ______ effect.

Back 92

Second gas effect

Front 93

True or false. When using nitrous oxide it is substituted for oxygen.

Back 93

False, added to oxygen, not substituted
-Used at 50-67% of total flow

Front 94

How long should you keep patients on oxygen when recovering from nitrous oxide and another inhalant anesthetic?

Back 94

At least 5 minutes

Front 95

True or false. Using nitrous oxide decreases the cost of anesthesia.

Back 95

false, increases anesthesia costs

Front 96

Normally we would use 2% isoflurane at 1 LPM and oxygen at 20 mL/min of isoflurane vapor, if you use nitrous oxide how does this change?

Back 96

1.5% isoflurane at 1 LPM, oxygen & 1 LPM nitrous oxide= 30 mL/min of isoflurane vapor

Front 97

With regards to anesthetic uptake and distribution, with anesthesia we assume that the concentration of anesthesia in the brain= what 3 things?

Back 97

[brain]=[arterial]=[alveolar]=[end tidal]

Front 98

The uptake and distribution of an anesthesia depends on what 5 things?

Back 98

1) Agent solubility
2) Vaporizer setting
3) Flow rate
4) Cardiac output
5) Ventilation

Front 99

What are the effects of higher solubility of an anesthetic agent?

Back 99

the alveolar concentration will become equal to (closer to) the concentration of the inspired gas
e.g. nitrous oxide is highly soluble and the alveolar concentration rapidly reaches the inspired concentration

Front 100

What are the effects of increasing flow rate w/ regards to Finspired/Fdelivered?

Back 100

The higher the flow rate the more rapidly the inspired concentration approaches the concentration of the anesthetic delivered

Front 101

How does the cardiac output affect Falveolar/Finspired?

Back 101

As the cardiac output increases the ratio of alveolar to inspired decreases

Front 102

How is the Falveolar/Finspired affected by increase in ventilation?

Back 102

Increase ventilation then increase the ratio

Front 103

What is the path of the anesthetic after it leaves the vaporizer?

Back 103

Pdelivered---> Pcircuit--->Pinspired---->Palveolar---> Parterial---> Pbrain---> Parterial--->Palveolar-->exhaust

Front 104

What are the 7 factors that affect the recovery of an animal from anesthesia?

Back 104

1) Agent solubility
2) Oxygen flow rate
3) Cardiac output
4) Ventilation
5) Body temperature
6) Background medications
7) Duration of anesthesia (to a point)