Inhalation Agents

Question 1

Name two anaesthetics that were discovered first.

Answer 1

Ether and chloroform

Question 2

What is the commonest application of inhalation agents as anaesthetics?

Answer 2

As maintenance of anaesthesia
Can also be used in paediatrics as induction agents as they are more anxious

Question 3

Name 5 commonly used inhalation anaesthetics.

Answer 3

Halothane
Nitrous oxide
Sevoflurane
Isoflurane
Desflurane

Question 4

Explain what minimum alveolar concentration is.

Answer 4

The alveolar concentration of inhaled anaesthetic that prevent movement in 50% of patients in response to a stimulus(such as a surgical stimulation)

Note: It is considered an anaesthetic’s ED50

Question 5

Is the administration goal for inhalation anaesthetic the minimum alveolar concentration?

Answer 5

Nope, since 50 % of patients move in response to a stimulus at the minimum alveolar concentration(remember MAC is the alveolar concentration of inhalation anesthetic that prevents movement in 50% of patients in response to a stimulus)

Question 6

List 12 desirable properties of an Inhaled anaesthetic.(Even more than that)

Answer 6

1. Involving the anaesthesia machine and breathing circuit
   -Lack of flammability
   -Easy to vaporise at room temperature
   -Chemically stable
2. Involving the lungs and breathing
   -Rapid induction and emergence
   -lack of airway irritation
   -Bronchodilator
   -Lack of respiratory depression
3. Involving cardiovascular system
   -Maintenance of mean arterial pressure
   -Suppression of sympathetic nervous system activity
   -Maintenance of heart rate
4. Involving other organ systems
   -Low solubility to skeletal muscles and fat
   -lead to direct muscle relaxation
   -Should not be a trigger of malignant Hyperthermia
   -Low hepatic metabolism
   -Lack of organ toxicity
5. Involving central nervous system
   -Analgesia
   -High potency

Question 7

Is nitrous oxide flammable?

Answer 7

Yes

Note: It is of concern in procedures using lasers or cautery in air spaceswhich could contain the drug.

Question 8

Is nitrous oxide volatile?

Answer 8

Nope, it is typically supplied from the wall outlet

Question 9

Name an anaesthetic gas that requires specialized and pressurised vaporiser and state why.

Answer 9

Desflurane
Why: Its boiling point is close to the room temperature

Question 10

Name a substance found in the canister of the anaesthesia machine that absorbs carbon dioxide.

Answer 10

Soda lime

Question 11

Name a byproduct formed when sevoflurane reacts with the soda lime.

Answer 11

Vinyl compound that is nephrotoxic

Question 12

Name a byproduct of desflurane that forms after it reacts to soda lime.

Answer 12

Carbon monoxide

Note: To a lesser extent Isoflurane forms carbon monoxide as well

Question 13

How is the chemical stability of the newer anesthetic gases as compared to the older ones?

Answer 13

They are more stable than the older agents (meaning they produce a low quantity of toxic substance after reacting to soda lime)

Question 15

What is the relationship between solubility or an anesthetic gas in blood and speed of induction?

Answer 15

Inverse relationship: Soluble gases have a slower speed of induction

Question 16

Outline the order of anaesthetic gases based on:
1. Solubility in blood(Start with insoluble substance)
2. Lipid solubility(More soluble first)

Answer 16

1. Desflurane=>Nitrous oxide==>Sevoflurane===>Isoflurane====>Halothane
2. Sevoflurane=>Isoflurane==>Desflurane===>Nitrous oxide(It is not lipid soluble)

Question 17

Why is the lipid solubility of an anesthetic gas considered a double edge sword?

Answer 17

If an anesthetic is soluble in fat, then body fat can act as a depot in which the anesthetic can accumulate, thus slowing emergence

However it can penetrate the brain more easily.

Note: Since the fat cells have little blood flow, accumulation in fat occurs over a long period of time.

Question 18

Name two anesthetic gases that have limited airway irritation.

Answer 18

Sevoflurane
Nitrous oxide

Question 19

Outline the anaesthetic gases in order of potency.

Answer 19

Isoflurane(MAC:1.15%)==>Sevoflurane(MAC:2.04%)==>Desflurane(MAC:6%)==>Nitrous oxide(MAC:104%)

Question 20

Is desflurane more potent than sevoflurane?

Answer 20

Nope, sevoflurane MAC is 2.04% while desflurane MAC is 6%

Question 21

Can desflurane be used as an induction agent? Why or why not?

Answer 21

Nope only maintenance as it is an airway irritant and has a very strong smell. Thus can trigger coughing and laryngospasm

Question 23

What is the effect of desflurane on the airway in smokers?

Answer 23

Bronchoconstriction

Note: No effects on non smokers

Question 24

Name two anaesthetic gases that are bronchodilators as well.

Answer 24

Sevoflurane and Isoflurane

Question 25

Does nitrous oxide have an effect on airway resistance?

Answer 25

No effect Note: Also desflurane in non smokers

Question 26

Are all inhaled anaesthetics respiratory depressants?

Answer 26

Yes Summary of their effect: 3Rs

Question 27

List three effects of all inhaled anaesthetics on the respiratory system.

Answer 27

Causes: Rapid respiration Reduction in tidal volume Loss of the awake respiratory variability

Question 28

Do inhaled anaesthetics increase arterial carbon dioxide? Also list associated effects as well.

Answer 28

Yes(except for nitrous oxide) Other effects: Depress the ventilatory response to hypercarbia in anesthetic concentrations, and most importantly, Depress the ventilatory response to hypoxia even in sub-anesthetic concentrations.

Question 29

Do inhaled anaesthetics increase or depress the ventilatory response to hypoxia and Hypercarbia?

Answer 29

Yes: Hypoxia: In sub anaesthetic concentration in addition to anesthetic concentration Hypercarbia: Only in anaesthetic concentration

Question 30

Name an Inhaled anaesthetic that does not drop blood pressure.

Answer 30

Nitrous oxide Others drop blood pressure.

Question 31

Name three inhaled anaesthetics that increase sympathetic activity.

Answer 31

Desflurane, Isoflurane and nitrous oxide Note: This is dose dependant

Question 32

Does inhaled anaesthetics have an infection on muscle?

Answer 32

Yes they cause muscle relaxation (only nitrous oxide has little effect on the muscles) Order: Desflurane, Sevoflurane then isoflurane

Question 33

Name three inhaled anaesthetics that trigger Malignant Hyperthermia.

Answer 33

Desflurane, Isoflurane and sevoflurane

Question 34

Summarise the rule of 2s of herpetic metabolism of inhaled anaesthetics

Answer 34

Halothane 20% Sevoflurane 4% (2x2) Enflurane 2% Isoflurane 0.2% Desflurane 0.02% Note: Nitrous oxide metabolism is negligible

Question 35

Name three inhaled anaesthetics associated with hepatic toxicity.

Answer 35

Halothane Desflurane Isoflurane

Question 36

Name one inhaled commonly associated to ith renal toxicity.

Answer 36

Sevoflurane which forms compound A.

Question 37

Name an Inhaled anaesthetic associated with bone toxicity.

Answer 37

Nitrous oxide

Question 38

Name four volatiles to avoid if someone has a history of hepatitis.

Answer 38

Halothane Sevoflurane Isoflurane Desflurane

Question 39

Name the only inhaled anaesthetic that is a potent analgesic.

Answer 39

Nitrous oxide Effect can be blocked by naloxone

Question 40

List 6 advantages of nitrous oxide.

Answer 40

Analgesia Fast induction and emergence Negligible hepatic metabolism Not pungent Less cardiovascular effects Less respiratory depression

Question 41

State 6 disadvantages of nitrous oxide.

Answer 41

Triggers nausea and vomiting Low potency Lead to sympathetic activation Bone marrow toxicity Expands air filled cavities Support combustion

Question 42

State four advantages of Isoflurane.

Answer 42

High potency Bronchodilator Low hepatic metabolism Cheap

Question 43

List 5 disadvantages of Isoflurane

Answer 43

Slower induction and emergence Highly soluble in fat and muscle Pungent odor Strong vasodilator Trigger Malignant Hyperthermia

Question 44

List three advantages of desflurane.

Answer 44

Fastest induction and emergence Low blood solubility Very low hepatic metabolism

Question 45

List 7 disadvantages of desflurane.

Answer 45

Very purulent odor Need specialized vaporisers Triggers malignant hyperthermia Forms carbon monoxide Activate the sympathetic nervous system Triggers bronchoconstriction in smokers Cause hypotension

Question 46

List 7 disadvantages of sevoflurane

Answer 46

High hepatic metabolism (about 4%) High inorganic fluoride ion levels Compound A formed in CO2 absorbent Bronchodilator Potential renal toxicity Most soluble in fat and muscle Hypotension (vasodilator) Trigger for malignant hyperthermia

Question 47

State 4 advantages of sevoflurane.

Answer 47

Faster induction and emergence Pleasant odor (not pungent) Suitable for mask induction (in children) Bronchodilator

Question 48

A 30-year-old man presents for open reduction and internal fixation of a left radius fracture as an outpatient. He has smoked 1 pack of cigarettes per day for 12 years. The plan is general anesthesia with endotracheal intubation. Which one of the following agents is most appropriate for him? A. Isoflurane B. Sevoflurane C. Desflurane D. Nitrous oxide

Answer 48

B. Sevoflurane Why Isoflurane is wrong: It is more soluble in blood which causes it to have slower induction and emergence. Why desflurane is wrong: It triggers bronchoconstriction in smokers and it is highly irritating to the airway Why not nitrous oxide: It has the lowest potency and is never used alone.

Question 49

A 42-year-old woman presents for laparoscopic gastric bypass. She weighs 191 kg (420 lb) and is 165 cm (5 ft and 5 in) tall. She has a history of hypertension, diabetes mellitus, obstructive sleep apnea, and acid reflux. Because of the sleep apnea, there is concern about mild pulmonary hypertension. Which of the following agents is most likely to produce the most rapid emergence in this patient? A. Isoflurane B. Sevoflurane C. Desflurane D. Nitrous oxide

Answer 49

C. Desflurane. Why are others wrong Isoflurane and sevoflurane: This patient is morbidly obese and they have the highest fat solubility meaning most of the gas will be taken up by the fat reducing the induction and emergence speed. Nitrous oxide is never used alone and is contraindicated in pulmonary hypertension

Question 50

A 38-year-old man presents for ventral hernia repair. He had a malignant hyperthermia crisis during a prior surgery. Which of the following inhaled anesthetics would be appropriate for this patient? A. Isoflurane B. Sevoflurane C. Desflurane D. Nitrous oxide

Answer 50

D. Nitrous oxide Why: Others trigger Malignant Hyperthermia

Question 51

Name four drugs used in anaesthesia tha trigger Malignant Hyperthermia.

Answer 51

Sevoflurane Isoflurane Desflurane Suxamethonium(Succinylcholine)

Question 52

What is the mainstay treatment for malignant hyperthermia?

Answer 52

IV dantrolene