Lecture 6: Inhalation Agents

Question 1

What was the earliest anesthetic?

Answer 1

Ether

Question 2

T/F: All inhalation agents have a low blood:gas solubility coefficient in common.

Answer 2

True.

This creates a favorable pharmacokinetic profile and promotes their clinical use today.

Question 3

A chemical bond that involves the sharing of electron pairs between atoms is called a _______.

Answer 3

Covalent Bond.

The stable balance of attractive and repulsive forces between atoms when they share electrons is known as covalent bonding. For many molecules, the sharing of electrons allows each atom to attain the equivalent of a full outer shell, corresponding to a stable electron configuration.

Question 4

Match the following Covalent Bonds with their names.

1. Alkane a. C=C
2. Alkene b. C-C
3. Alkyne c. CEC (E= 3 lines, or 3 bonds)

Answer 4

1. Alkane b. C-C
2. Alkene a.C=C
3. Alkyne c. CEC (E=3 lines, or 3 bonds)

simple way to remember. Ane, Ene, Yne follow alphabetical order. A=1 bond, E=2 bonds, Y=3 bonds.

Question 5

Chemical Structure and Agent Characteristics:

All commonly used inhalations are ethers or aliphatic hydrocarbons with no more than ___ carbon atoms.

Answer 5

4 (no more than 4 carbon atoms)

Question 6

Chemical Structure and Agent Characteristics:

Why is the length of the molecule significant?

Answer 6

Anesthetic effect of immobility is decreased or lost if carbon atom chain length exceeds a distance of 4-5 carbon atoms 5 angstroms.

Question 7

Chemical Structure and Agent Characteristics:

What is meant by “Halogenated” hydrocarbons?

Answer 7

Halogens are substituted for Hydrogen atoms in the chemical structure.

Question 8

Chemical Structure and Agent Characteristics:

What are the halogen gases are attached to the molecules? (hint: there are 4 of them)

Answer 8

F (Fluorine)
Cl (Chlorine)
Br (Bromine)
I (Iodine)

Question 9

Chemical Structure and Agent Characteristics:

The addition of F, Cl, Br, or I provide what characteristics to an anesthetic gas? (hint: 4 items)

Answer 9

• Potency
• Arrhythmogenic properties
• Flammability
• Chemical stability

Question 10

Halogenated gases:

How is potency impacted by halogenation?

Answer 10

Potency increases as the amu (atomic mass unit) of a halogen increases.
Bromine 80 amu vs. Fluorine 19 amu. Bromine will be more potent.

Potency of inhalation agent has been found to correlate with the physical property of lipid solubility. A decline in potency (increased MAC value) is not a perfect correlation.

Question 11

Halogenated gases:

How is Arrhythmogenesis impacted by halogenation?

Answer 11

INCREASING the number of halogen atoms within a volatile agent FAVORS the occurrence of arrhythmia.

Question 12

Halogenated gases:

How is Flammability and Chemical Stabilty impacted by halogenation?

Answer 12

Flammability is REDUCED and Chemical Stability is ENHANCED by substituting hydrogen atoms with halogens.

Question 13

What are Aliphatic Hydrocarbons?

Answer 13

a compound containing carbon and hydrogen joined together in straight chains, branched trains or non-aromatic rings.

Question 14

What are the halogens?

Answer 14

• Halogens are a group in the periodic table consisting of 5 chemically-related elements (F, Cl, Br, I and Astatine). Known as (vertical) group 17.
• It is the only group to contain elements in 3 states at standard temperature (gas F and Cl, liquid Br, and solid I).
• All are toxic.
• All of the halogens form acids when bonded to hydrogen.

Question 15

All modern inhaled anesthetics are halogenated hydrocarbons except_______?

Answer 15

Nitrous Oxide

Question 16

Metabolism:

Typically, increasing the number of _____atoms on an anesthetic molecule will ______ the rate biodegradation.

Answer 16

FLUORINE;

SLOW or DECREASE

Question 17

Anesthetic gases mostly excreted by the _____ and to a small extent metabolized by the _____.

Answer 17

• Excreted by the lungs unchanged.
• metabolized by the liver.

Halothane= 45% metabolized by liver (halothane hepatitis; rarely used)
Sevofluorane=5-8% metabolized by liver
Isofluorane=0.2% metabolized by the liver
Desflurane=0.02% metabolized by liver

Question 18

T/F: All anesthetic gases are non-ionized.

Answer 18

True.

• All are non-ionized (not charged, neutral molecular compounds), strong covalent bonding.
• All have low molecular weight.

Question 19

The goal of inhalation anesthesia is to produce the anesthetic state by creating a specific concentration of anesthetic molecules in the CNS. This is done by establishing a ____ _____ of an agent in the lungs, which then _______s with the brain and spinal cord.

Answer 19

Partial Pressure

Equilibrates

-with partial pressure equilibrium, the gas redistributes and is exhaled.

Question 20

The anesthetic gases ______ the effects of stress from surgical stimulus, and _______ the occurrences of arrhythmias.

Answer 20

Attenuate/decrease

increase.

Question 21

Pharmacodynamics:

Lipid solubility is directly proportional to ______. (Meyer-Overton rule)

Answer 21

Potency.

The potency of an anesthetic increases as the liposolubility increases.

Question 22

Pharmacodynamics:

T/F: Reversal of anesthetic can be achieved with the application of pressure.

Answer 22

True.

Question 23

Pharmacodynamics:

The exact mechanism of action is not well understood, however it is understood that the spinal cord and brain stem are effected and the _____ receptors are play a role in anesthesia effects.

Answer 23

GABA

Question 24

Define MAC

not monitored anesthesia care

Answer 24

Minimum Alveolar Concentration (at MAC value, 50% of people will NOT respond to surgical stimulation.)

Question 25

Blood:Gas solubility coefficient determines ______.

Answer 25

Speed of uptake and elimination.

HIGH solubility= SLOWER uptate and elimination
LOW solubility= FASTER uptake and elimination

Question 26

Oil:Gas partition coefficient determines_______.

Answer 26

Potency

HIGH oil:gas = HIGH potency

The potency of an anesthetic increases as it’s liposolubility increases. (Crosses the blood-brain barrier more easily)

Question 27

Cellular activity:
Inhaled anesthetics “probably” produce anesthesia by ENHANCING THE FUNCTION OF INHIBITORY ION CHANNELS AND BY BLOCKING FUNCTION OF THE EXCITATORY ION CHANNELS.

In what way does this occur and what receptors are involved?

Answer 27

Hyperpolarization of cells.

This results from an influx of chloride anions entering neurons through GABA receptors or glycine receptors and an efflux of potassium cations leaving the cell causing hyperpolarization and inhibiting an action potential from occurring.

Question 28

Immobility:

Immobility is mediated through what organ?

How is MAC value related to immobility?

Answer 28

Spinal cord mediated.

At 1 MAC, 50% of people don’t move in response to surgical stimulus.

The length of of an anesthetic molecule is significant that “immobility is lost” of a carbon atom chain length exceeds 4-5 carbon atoms (5 angstroms)

Question 29

The amygdala, hippocampus, and cortex are considered HIGHLY PROBABLE targets for the what effect of anesthetics?

Answer 29

AMNESIA (don’t forget)

Question 30

T/F: The BIS Monitor is the most reliable measure of anesthesia.

Answer 30

False. It is a piece of shit device, however is still commonly used and documented, however not relied upon for data of any clinical value. Used as adjunct to other clinical data.

Question 31

Do inhaled anesthetics have analgesic properties?

Answer 31

No. Intraoperative measures of pain suggest that inhaled anesthetics do not suppress the perception of painful stimuli. Increased HR and Increased BP are 2 indicators of intraoperative pain.

Question 32

At Equilibrium, CNS partial pressure will equal what other partial pressures. (hint: 2 different partial pressures)

Answer 32

Palveoli=Pblood=PCNS