Volatile Anesthetics

Question 1

Characteristics of volatile anesthetics (3)

Answer 1

1. Small molecular weight, volatile compounds
2. Administered as gases or vapors via inhalation
3. Most are fluoridated

Question 2

The goals of creating fluoridated anesthetics: (3)

Answer 2

1. Reduce or eliminate toxicity (metabolism)
2. Reduce or eliminate flammability
3. Allow more rapid induction and recovery from anesthesia
   * worry about toxicity to the kidney and the liver

Question 3

Fluoridated Anesthetics: Basic hydrocarbon structures most useful as fluoridated anesthetics: (3) structures

Answer 3

1. Ethane- early 60s= halothane. No ethane currently use. Two carbon molecules bound together
2. Methyl ethyl ethers= most common structure. (Example: iso, des)
3. Isopropyl methyl ether= small molecule weight compound. Addition of methyl group
   * only small molecules have the high valiantly required of inhaled anesthetics (cannot just add something to make it a better anesthestic)

Question 4

Nitrous Oxide

Answer 4

1. Very good add on anesthetic. Rapid onset- but won’t completely put patient to sleep. Good analgesia too. Once it is turned off it was dissipate quickly
2. Synthesized in 1776, deemed failure, then reintroduced in 1863
3. Currently used mostly ad adjunct to other agents to lower dose of other required anesthetics
4. Supports combustion- can serve as oxidant (instead of O2) to fuel a fire
5. Only anesthetic supplied in steel cylinders (BP= -88C) Stored as a liquid
   Note: N2O= one nitrogen must be charged

Question 5

Ether (Diethyl Ether)

Answer 5

1. Two ethyl groups bound by an oxygen. First complete anesthetic. Demonstrated publicly in 1846.
2. More potent than nitrous oxide minimal organ toxicity
3. FLAMMABLE* and patients very nauseous when waking up- very lipid soluble so induction and wake up was very slow*

Question 6

Chloroform

Answer 6

1. Introduced in 1847- predates civil war.
2. First halogenated anesthetist
3. Halogen odor- sweet- good for kids
4. Nonflammable (due to the high degree of halogenation). Chlorines hinder oxidation*
5. Used until early 1900s, patients dying from liver toxicity*

Question 7

Cyclopropane

Answer 7

1. Discovered in 1929. Tested at U of W, used for 30 years
2. Flammable*
3. Explosive under right conditions, ring strain increases instability (more susceptible to oxidation and flammability)
4. good anesthetic-rapid induction and recovery

Question 8

Methyl Ethyl Ether: Methoxyflurane (Penthrane)

Answer 8

1. Two chlorine and No halogens
2. More analgesia than other volatile anesthestics
3. Non flammable, no preservative.
4. Associated with renal toxicity (poly uric dysfunction- excess urine, release of inorganic fluoride- resulting from metabolism of this)
5. No longer used in US- but still is in Australia in a self administered handheld vaporizer for procedural analgesia

Question 9

Enflurane (Ethrane)

Answer 9

1. More highly fluoridated than methoxylfurane (added 3 fluorines)
2. More resistant to metabolism that occurs in liver by p450= less liver toxic (less fluorine released)
3. More stable and more volatile than methoxyflurane
4. Releases much less fluoride than methoxyflurane, but more than halothane and desflurane

Question 10

Isoflurane (Forane)

Answer 10

1. Structural isomer of enflurane
2. Widely used volatile anesthetic
3. Few problems of toxicity are associated with it
   * rather expensive

Question 11

Sevoflurane (Ultane)- isopropyl anesthetic

Answer 11

1. Metabolized more than iso, enflurane and desflurane
2. Least stable anesthetic to soda lime or other basic CO2 absorbents
3. Rapid onset and recovery from anesthesia- similar to desflurane, but slightly slower.
4. Pleasant to inhale= good for kids*** (only agent you can induce with)
   Early 1990s, trying to develop an anesthetic that was faster onset

Question 12

Desflurane

Answer 12

1. Always going to be more expensive because you first start with isoflurane and then add another fluorine (which makes it more stable). Differs from isoflurane by one atom, a fluorine for a chlorine
2. More volatile than all other fluoridated anesthetics
3. Very stable and inert to metabolism
4. Rapid onset and recovery from anesthesia
5. Heart irregularity is noted with this ****

Question 13

Halothane

Answer 13

1. Introduced in 1956
2. Only ethane anesthestic
3. Sweet odor, non pungent
4. Hepatoxicity associated with this*****
   (Renal issues were dismissed because it did not release fluorines)
5. Halothane hepatitis= 60s-70s noted in female, obese patients, never associated with kids so continued to use in kids*

Question 14

Halothane: the anesthetic preparation of Halothane (liquid) contains ____________ as an inhibitor or preservative?

Answer 14

1. Thymol
2. None of the other volatile anesthetics contain any other preservative- others are pure compounds.
   * propofol like in its antioxidant effects

Question 15

Halothane Liver Toxicity

Answer 15

1. Associated with liver toxicity more than any other volatile anesthetic
2. Fatal cases of halothane hepatitis occur at a rate of 1 in 30,000 patients anesthetize.
3. Toxicity is though to be related to halothane metabolism (does NOT release fluorine- it has a reactive metabolite from p450 enzyme oxidizing the molecule and creating a species which will react with macromolecules in the environment= acteyl chloride- bind with liver tissue can cause toxicity ***