Inhalant Anesthetic Agents

Front 1

What are the 5 most common Inhalant Anesthetic Agents?

Back 1

1. Isoflurane
2. Halothane
3. Nitrous Oxide
4. Methoxyflurane (not used)
5. Sevoflurane (newest)

Front 2

What characteristics would the "Ideal" inhalation agent have?

Back 2

a) Minimal toxicity (cardio, respir, hepatic, renal, nervous)
b) Minimal toxicity of waste gas vapors to personnel
c) Ease of administration
d) Rapid & gentle induction and recovery
e) Anesthetic depth easily controlled and altered
f) Good muscle relaxation & postoperative analgesia
g) Low cost
h) Adequate potency to achieve surgical anesthesia
i) Nonflammable & nonexplosive (safe to handle)
j) No need for expensive equipment

Front 3

Is there an "Ideal" Inhalant agent?

Back 3

There is NO ideal agent!

Front 4

What is commonly considered when selecting an inhalation anesthetic agent?

Back 4

5 Things to consider when selecting an inhalation agent:
1. Availablity
2. Cost
3. Preference of anesthetist & surgeon
4. Special needs of the patient
5. Procedure being performed

Front 5

What are the 3 Classes of Inhalent Anesthetic Agents?

Back 5

1. DIETHYL ETHER
2. NITROUS OXIDE
3. CHOROFLUOROCARBONS

Front 6

What are the characteristics of Diethyl ether?

Back 6

a) Maintains realtivley stable cardiac output
b) No sensitization of heard arrhythmias
c) Good muscle relaxation
d) Good analgesia
e) VERY irritating to trachebronchial mucosa
f) Prolonged recovery
g) HIGHLY flamable and explosive

Front 7

Mechanism of action

Back 7

Unknown but appear to inhibit GABA breakdown allowing increased inhibition of nervous system tissues

Front 8

What is occuring in the body during the induction phase?

Back 8

a) Transferred via air passages to the alveoli
b) Diffuses into the blood stream via the alveolar capillaries
c) Readily leave circulation and enter the bloodstream due to their HIGH LIPID SOLUBLILTY leading to anesthesia

Front 9

Describe vapor pressure and its importance.

Back 9

The percentage of inhalation anesthetic that will evaporate at 20 Degrees C. HIGH VAPOR PRESSURE ARE LABLED VOLATILE. Vapor pressure determines to what concentration an anesthetic gas can be present in the patient and effects how it may be delivered.

Front 10

What is solubility coefficiant?

Back 10

A measure of the distribution of the inhalation agent between the liquid (blood) and gas (alveoli) phases in the body.

Front 11

Does high or low solubility coeffiecient produce a rapid induction? Why?

Back 11

Low solubility coefficient. Tends to remain in the gas phase and do not solubilize in the blood easily; increases concentration in the alveoli, enter the bloodstream rapidly then rapidly exits into brain; this leads to rapid induction & recovery.

Front 12

What is lipid solubility?
How does that effect "Hangover Time"?

Back 12

The affinity of the gas for solubilization in lipids.
High lipid solubility - attracted to fats (sponge effect, increased hangover)
Low lipid solubility - Drug will be exhaled (decreased hangover time)*Easier to eliminate-Better*

Front 13

What is Minimum Alveolar Concentration (MAC)?
Does high or low MAC indicate increased potency

Back 13

The lowest concentration of anesthetic gas that will yield no response to a painful stimulus in 50% of patients, Indicates the potency of an anesthetic.
Low MAC= increased potency

Front 14

MAC-Minimum Alveolar Concentration

Back 14

Low MAC= increased potency
High MAC= decreased potency
1. Dial setting of 1 X MAC=
Light anesthesia
2. Setting of 1.5 X MAC=
Surgical anesthesia
3. Setting of 2 X MAC=
Deep anesthesia

Front 15

Whats occuring during the Maintenance phase of anesthesia:

Back 15

By keeping the inhaled anesthetic concentration at a maintaned level, an equilibrium is established between alveoli, blood, & brain, keeping animal anesthetized.

Front 16

Whats occuring during the Recovery phase:

Back 16

By decreasing the anesthetic level in the alveoli, concemtration gradients causing the gas to leave the bloodstream and be exhaled, causing the gas to exit the brain and animal to recover.

Front 17

Methoxyflurane:
What type of vaporizer is used?

Back 17

Wick Vaporizer
-due to low vapor pressure

Front 18

Methoxyflurane:
How potent is it?

Back 18

-**Most potent of commonly used drugs!
-High solubility coefficient causes the longest induction, longest recovery (although smooth recovery), and slow changes in anesthetic depth.

Front 19

Methoxyflurane:
How much is metabloized?
Why?

Back 19

*50% is metabolized
-High lipid solubility leads to a great amount of metabolism

Front 20

Methoxyflurane:
What type of disease should it NOT be used in?

Back 20

**Do NOT use in patients with known renal problems!
-May cause renal problems

Front 21

Methoxyflurane:
How does it effect the Cardiovascular/Respiratory Systems?

Back 21

Cardio/Respiratory effect:
1. *Most potent respiratory depressant.
2. No sensitization to arrhythmias
3. Decreases contractility of the heart up to 40% causing severe decreases in cardiac output.
(marked muscle relaxation)

Front 22

Methoxyflurane:
How much Analgesia does it produce?

Back 22

*Profound Analgesia, intra & post operatively

Front 23

Halothane:
What type of vaporizer is required?

Back 23

-*Precision Anesthetic Vaporizer
(due to high vapor pressure)

Front 24

Halothane:
What type of Induction/Recovery time does it have?
Why?

Back 24

-Intermediate Induction
**(due to moderate solubility coefficient)
-Intermediate Recovery time
-Moderately fast changes in anesthetic depth

Front 25

Halothane:
How much is Metabolized?

Back 25

10-20% metabolized

Front 26

Halothane:
What disease should it NOT be used in?

Back 26

Avoid use in Hepatic Disease!

Front 27

Halothane:
What are the effects on the Cardiovascular/Respiratory Systems?

Back 27

Cardio/Respiratory effects:
1. Some respiratory depression
2. Sensitizes the heart to catecholamines causing arrhythmias (catecholamines released from pain, adequate anesthetic depth will solve problem)
3. Increases vagal tone & decreases cardiac output causing lowered blood pressure
(adequate muscle relaxation)

Front 28

Halothane:
How much Analgesia does it produce?

Back 28

-Moderate analgesia
-Moderate post-surgical analgesia
(can cause hypothermia due to vasodilation & an increase in cranial pressure)

Front 29

Halothane:
*Associated w/ Malignant Hyperthermia

Back 29

Malignant Hyperthermia: a rare condition where animals show increased temperature, muscle rigidity, cardiac arrhytmias and possible death! (Greyhounds & Pigs)

Front 30

Isoflurane:
*Most Common Drug Used*
What type of vaporizer should be used?

Back 30

A Precision Anesthetic Vaporizer
(due to a high vapor pressure)

Front 31

Isoflurane:
What types of Induction is it commonly used for?

Back 31

Mask and Chamber Inductions
-Low solubility coefficient allows rapid changes of anesthetic depth
-Rapid Induction and Recovery

Front 32

Isoflurane:
How much is metabolized?

Back 32

0.25% metabolized

Front 33

Isoflurane:
What disease should it NOT be used in?

Back 33

Absolute contraindications: family history of Malignant Hyperthermia

Front 34

Isoflurane:
What effects does it have on Cardiovascular/Respiratory Systems?
Muscle relaxation?

Back 34

Cardiovascular effect:
1. Heart rate, rhythm, blood pressure
2. No sensitization to arrhythmias
3. Depresses respiration (more than halothane, but less than methoxyflurane)
4. Decreased blood pressure
-Good muscle relaxation

Front 35

Isoflurane:
How much Analgesia does it produce?
What are undesirable effects?

Back 35

-Good Analgesia
-Poor Post-Operative Analgesia (due to low metabolism)
-* Chance of increased intracranial pressure

Front 36

Nitrous Oxide:
Can this be used alone to produce anesthesia?
Why or Why not?

Back 36

-Unachievable concentrations for anesthetic as a gas by itself* (high MAC)
-Must be used an adjunct to anesthesia w/ other gases
-Used w/ other agents allows decreased concentration of other agents used (MAC of other agent decreased 20-30%)

Front 37

Nitrous Oxide:
What is "Second Gas Effect"?

Back 37

Speeds induction & recovery when used at high concentrations (50-70%)
-Extremely low solubility coefficient (enhances uptake of other gases)

Front 38

Nitrous Oxide:
What are the dangers due to its solubility coefficient?

Back 38

Dangers:
1. Diffusion into Air Pockets: poor choice w/ intestinal obstruction, GDV, pneumothorax, diaphragmatic hernia, any Ruminant
2. Diffusion Hypoxia: speedy exit at end of anesthesia causes oxygen in alveoli to be replaced by notrous oxide, to avoid, maintain high oxygen flow for 5 min after nitrous turned off.

Front 39

Nitrous Oxide:
How does it effect muscle relaxation?
What type of Analgesia does it produce?

Back 39

-Good muscle relaxation
-Good Analgesia

Front 40

Nitrous Oxide:
What are the undesirable effects?

Back 40

Undesirable Effects: increased intracranial pressure, reduced liver blood flow, bone marrow suppression w/ chronic exposure, combustable fire hazard, not absorbed by activated charcoal scavenging devices

Front 41

Nitrous Oxide:
What are its Contraindications?

Back 41

Patients with or at risk of Cardiac Arrhythmias, AVIAN Anesthesia, Pulmonary Disfunction, patients w/ Increased Intracranial Pressure, Pneumothorax, GDV, Exploratory Laparotomy, Intra-Ocular procedures, Pre-Existing Bone Marrow disease, Unregulated Hyperthyroidism

Front 42

Nitrous Oxide:
Other Precautions that must be taken

Back 42

-Mixing Nitrous Oxide w/ Oxygen causes increased risk of *Hypoxia
-Do NOT use in Closed Systems: Oxygen is removed, Nitrous Oxide is not, therefore increasing levels of nitrous oxide will occur w/ prolonged anesthesia

Front 43

Sevoflurane:
What type of Vaporizer is needed?

Back 43

*Newest anesthetic agent-requires vaporizer Made for Sevoflurane

Front 44

Sevoflurane:
How potent is it?
Any reported Toxicity?

Back 44

-*Least potent of ALL except Nitrous Oxide, Higher concentrations will be necessary (due to Higher MAC)
-*No reported Toxicity*
(Low % Metabolized)

Front 45

Sevoflurane:
How does it effect Cranial Pressure?
What type of Analgesia produced?

Back 45

-Slight chance of Increased Cranial Pressure
-Poor Analgesic

Front 46

Sevoflurane:
What are the Contraindications?

Back 46

Family history of
Malignant Hyperthermia

Front 47

Sevoflurane:
How does it effect the Cardiovascular/Respiratory System?

Back 47

Cardio Respiratory effects:
1. Severe Respiratory Depression
2. Dose Dependent Depression of Cardiac Contractility
3. Vasodilation