Volatile Anesthetics

Question 1

What are the common contraindications of N2O use?

Answer 1

1: Concerns that expansion of air/gas-filled spaces can harm the patient, such as -
Emphysema
Pneumothorax
Middle ear surgery
Pneumocephalus
Air embolus
Bowel obstruction
Sulfur hexafluoride injected for intraocular surgery

2. Patients with critically elevated intracranial pressure
3. Recent craniotomy (within 3 weeks)
4. Known deficiency of enzyme or substrate in methionine synthase pathway

Question 2

Of note, N2O should not be used until _________ after sulfur hexafluoride has been injected into the eye during or after intraocular surgery

Answer 2

Three (3) months

Question 3

Relative contraindications to N2O use include:

Answer 3

1. Prolonged anesthesia >6 h
2. First trimester of pregnancy
3. Pulmonary hypertension
4. Very high risk of PONV, where TIVA would be more appropriate.

Question 4

T or F: BIS-guided anesthesia reduces the risk of intraoperative awareness and improves recovery time when compared to end-tidal anesthetic gas-guided anesthesia.

Answer 4

False

Question 5

Even though EEG-based monitoring is recommended with TIVA, age-adjusted MAC values of ____ - _____ are adequate to prevent awareness with recall.

Answer 5

0.7 - 1.0 MAC

Question 6

All commonly used inhalation agents are —?1— (R–O–R) or aliphatic —?2— (straight-chain or branched nonaromatic
hydrocarbons) with no more than —?3— carbon atoms

Answer 6

1. Ethers
2. Hydrocarbons
3. Four (The length of the anesthetic molecule is significant in that immobility (anesthetic effect) is attenuated or lost if the chain length exceeds four or five carbon atoms (5 angstroms [Å]).

Question 7

What is this?

Answer 7

The Lewis Structure of Isoflurane
1-chloro 2,2,2-trifluoroethyl difluroromethyl ether

Question 8

What is this?

Answer 8

The Lewis Structure of Sevoflurane
fluoromethyl 2,2,2,-trifuoro-1-(trifluoromethyl) ethyl ether

Question 9

What is this?

Answer 9

The Lewis Structure of Halothane
2-bromo-2-chloro-1,1,1-trifluroethane

(Note that without the halogen atoms on the carbons, it would be a simple hydrocarbon called Ethane)

Question 10

What is this?

Answer 10

The Lewis Structure of Desflurane
difluoromethyl, 1,2,2,2-tetrafluoroethyl ether

Question 11

Halothane is an example of a __________ .

Answer 11

Halogenated hydrocarbon

Question 12

Of primary importance to the development of inhalation agents was the discovery of the impact of _______ of organic compounds.

Answer 12

Halogenation

Question 13

Halogenation of hydrocarbons and ethers (the addition of ___1___ [F], __2__ [Cl], __3__ [Br], or __4__ [I]) influences anesthetic potency, arrhythmogenic properties, flammability, and chemical stability (e.g., oxidation during storage and reactions with bases).

Answer 13

Fluorine
Chlorine
Bromine
Iodine

Question 14

Anesthetic potency has been shown to increase when a halogen with a __1__ atomic mass unit (amu) is replaced by a __2__ halogen

Answer 14

1. Lower
2. Heavier (e.g., bromine at 80 amu substituted for fluorine at 19 amu). Nonetheless, a ceiling effect exists with halogenation of anesthetic compounds. For example, adding F atoms to ether results in a continuum in which the ether becomes more potent, then acts as a strong convulsant, and finally changes to an inert compound with full fluorination.

Question 15

In general, the potency of inhalation agents has also been found to correlate with the physical property of ________.

Answer 15

Lipid solubility
A decline in potency (meaning an increase in the minimum alveolar concentration [MAC] of inhalation agents) is associated with a proportional decrease in oil/gas partition coefficient values. Exceptions to this principle exist and demonstrate that the correlation between potency and lipid solubility is not perfect.

Question 16

With regard to arrhythmogenic properties, increasing the number of _________ within an inhalation agent favors the genesis of cardiac dysrhythmias.

Answer 16

Halogen atoms
Nevertheless, alkanes that contain five halogens (e.g., halothane) are more prone to induce arrhythmias than ethers
with six halogen atoms (e.g., isoflurane). This may be due to the lack of an oxygen molecule in halothane as compared to the ethers.

Question 17

Flammability of volatile anesthetics is reduced and chemical stability enhanced by substituting _____ with ____.

Answer 17

Hydrogen atoms with halogens
The epitome of this relationship is demonstrated with desflurane, a compound that contains fluorine as its only halogen and thus strongly resists biodegradation; desflurane is metabolized one tenth as much as isoflurane.

Question 18

What is an alkane?

Answer 18

Alkanes are the simplest of the organic compounds. Alkanes are characterized by carbon–carbon single bonds. Thus, alkanes are the carbon backbone for other functional groups. Methane (CH4) is the simplest alkane.

Question 19

If a hydrogen atom is removed from an alkane, it leaves an _________.

Answer 19

Alkyl group

Question 20

T or F: Alkyl groups are named by replacing “ane” on the alkane name with “yl.”

Answer 20

True
An alkyl group is a stickon group that is always connected to a molecular parent or to another group of atoms.

Question 21

Alkyl groups are generally symbolized by ____.

Answer 21

R.
So, when you see R in an organic structure, it means some generic alkyl group. It could be ethyl or methyl, and it really doesn’t matter. The R group is the carbon backbone of the molecule, and we can largely ignore it and focus on the functional groups.

This sort of generalization works in organic chemistry because the principal chemical and physical properties of a compound are determined by its functional groups, not the carbon backbone.

This is not to say, however, that the identity of the R group is absolutely irrelevant. As the R group becomes larger and bulkier, it does have an impact on the chemical and physical properties of the functional groups present. For example, since C–H and C–C bonds are essentially nonpolar, larger R groups increase the hydrophobic nature of the molecule. Also, as the R groups become bulkier and more congested (e.g., isopropyl compared to methyl), the R groups require more space and can prevent incoming reagent molecules from approaching or require incoming molecules to adopt a specific orientation. This is the key behind the remarkable specificity of enzymes.

Question 22

Inhalation anesthetics interact with the main repolarizing cardiac potassium channels (hERG) and IKs channels, as well as with calcium and sodium channels at slightly higher concentrations. Inhibition of these ion channels alters both action potential shape (triangulation) and electrical impulse conduction, which may facilitate arrhythmogenesis by inhalation anesthetics per se and is potentiated by catecholamines. Action potential triangulation by regionally heterogeneous inhibition of calcium (Ca2+) and potassium (K+) channels will facilitate catecholamine-induced afterdepolarizations, triggered activity, and enhanced automaticity. Inhibition of cardiac sodium channels will reduce conduction velocity and alter the refractory period; this is potentiated by catecholamines and promotes reentry arrhythmias.

Answer 22

Read again.