Inhalational Agents

Question 1

List the volatile AA.

Answer 1

Halothane
Isoflurane
Desflurane
Enflurane
Sevoflurane

Question 2

How is N20 (nitrous oxide) controlled and administered?

Answer 2

Flow meter

Question 3

How are the volatile agents controlled and administered?

Answer 3

Vapourisers

Question 4

What are the safety features of the vapourisers?

Answer 4

Colour coded

Specific colour coded keyed fillers with individual shapes (like puzzled pieces)

Question 5

Which volatile gas has a different vapouriser design to the others, and why?

Answer 5

Enflurane

Boiling point near room temperature

Question 6

Features of the ideal inhalational AA?

Answer 6

Cheap
Stable
No metabolism (fewer toxic effects)
Potent
No LT effects
Non irritant odour
No respiratory or cardiovascular depression
Hypnotic and analgesic
Readily reversible, neuroprotective and non-excitatory

Question 7

Which inhalational agents are suitable for a gas induction?

Answer 7

Halothane

Sevoflurane

Question 8

In which patients are gas inductions mostly used?

Answer 8

Children

Patients with compromised airways where patient continues to breathe spontaenously

Question 9

Factors affecting fiAA?

Answer 9

Volume of the breathing circuit
Fresh gas flow rate
Absorption of inhalational agent by breathing circuit

Question 10

Factors affecting alveolar concentration of AA (fA-AA)?

Answer 10

Inspired concentration
Uptake of the agent from the alveoli into the blood
Alveolar ventilation (RR)

Question 11

The inhalational AA uptake depends on…

Answer 11

Solubility of the agent in blood (blood to gas partition coefficient - BGPC)
Cardiac output
Alveolar to mixed venous partial pressure difference

Question 12

Factors affecting arterial concentration of AA (faAA)?

Answer 12

Shunting of blood

e.g. intrapulmonary (atelectasis, bronchial intubation) or intracardiac (ASD, VSD)

Question 13

Poorly soluble inhalational AA?

Answer 13

Desflurane
Sevoflurane
N20

Question 14

Highly soluble inhalational AA?

Answer 14

Halothane

Question 15

How do you assess the potency of an inhalational AA?

Answer 15

Looking at MAC (minimum alveolar concentration)

Question 16

Definition of MAC?

Answer 16

The steady-state minimum alveolar concentration (at sea level) that prevents movement to a standard surgical stimulus in 50% of non-premedicated adults.
MAC50

Question 17

Which is the most potent inhalational AA, and why?

Answer 17

Halothane

Highest fat solubility (brain is a fatty tissue)

Question 18

MACbar?

Answer 18

MAC-blocks autonomic response

Higher than MAC-50

Question 19

Factors that increase MAC (patient requires higher alveolar concentration to have ideal effect)?

Answer 19

Infancy
Hyperthermia
Hyperthyroidism
Catechloamines and sympathomimetics
Chronic opioid use
Chronic alcohol intake
Acute amphetamine intake
Hypernatraemia

Question 20

Factors that decrease MAC (patient requires lower alveolar concentration to have ideal effect)?

Answer 20

Neonates
Elderly
Pregnancy
Hypotension
Hypothermia
Hypothyroidism
Alpha-2 agonists
Sedatives
Acute opioid use
Acute alcohol intake
Chronic amphetamine intake
Lithium

Question 21

Factors that DO NOT affect MAC?

Answer 21

Gender
Duration of anesthesia
Time of day
Hypocarbia

Question 22

Inhalational AA vapouriser colours?

Answer 22

N20 - Blue (cylinder and pipeline)
Isoflurane - Purple
Sevoflurane - Yellow
Halothane - Red
Desflurane - Sky blue
Enflurane - Orange

Question 23

MAC of inhalational AA?

Answer 23

N20 - 105%
Isoflurane - 1,2%
Sevoflurane - 2%
Halothane - 0,75%
Desflurane - 6%
Enflurane - 1,7%

Question 24

N20 is also known as…

Answer 24

Laughing Gas

Question 25

Uses of N20 in anaesthesia?

Answer 25

Potent analgesic (but poor anaesthetic)
Used as carrier gas to deliver volatile agents
Used in reducing concentrations of volatile agents needed
Speeds up inhalational induction with another volatile agent ("second gas effect")

Question 26

What is Etonox?

Answer 26

Mixture of 50% N20 and 50% O2

Used for analgesia in lanour and minor ER procedures

Question 27

Toxic effects of N20?

Answer 27

PONV
Bone marrow depression is given for long periods
Addictive
3rd most abundant greenhouse gas

Question 28

Organ effects of Halothane?

Answer 28

Potent
Increases cerebral blood flow and ICP quite markedly compared to other agents
Slow recovery with hangover effect
Hypotension
Dysrythmias
Increased RR, decreases TV
Some muscle relaxation, including uterine
Mild elevation in liver enzymes post-op (Halothane hepatitis is a rare complication)

Question 29

Describe Halothane hepatitis?

Answer 29

Rare (1:35000)
Allergic phenomenon
Fulminant hepatic necrosis
50-75% mortality

Question 30

Organ effects of Isoflurane?

Answer 30

Less potent than Halothane
Least CNS effects (agent of choice in neuro-anesthesia)
Rapid recovery compared to Halothane
Good peripheral vasodilator - hypotension
Irritant to airways (not suitable for induction)
Isolated reports of liver enzyme elevation
Reduces total hepatic blood flow, while preserving hepatic arterial blood flow (best agent for patients with liver disease)
Relaxant

Question 31

Organ effects of Sevoflurane?

Answer 31

Relatively weak agent
Low solubility - fast induction
Mildly decreases SVR
May prolong QT interval
Does NOT induce arrythmias
Agent of choice for cardiac patients
Non-irritant (can be used for induction)
Used with caution in renal failure patients

Question 32

Characteristics of Desflurane?

Answer 32

Newest volatile agent
Expensive
Very small toxic potential
Rapid acting, but highly irritant and unpleasant (not suited for induction)
Most insoluble agent with the most rapid recovery
Rapid increases can lead to transient marked elevated HR, BP and catechloamine levels

Question 33

Characteristics of Enflurane?

Answer 33

Expensive
Practically obsolete
Unacceptable side effects
High concentrations may provide epileptiform EEG activity (avoid in epileptics)
Contraindicated in neurosurgery and renal problems