Inhalational Anaesthetics

Question 1

How are inhaled anaesthetics transported?

Answer 1

in carrier gasses

Question 2

Name 3 types of inhaled anaesthetics

Answer 2

• Halothane
• Isoflurane (MUST KNOW)
• Sevoflurane (MUST KNOW)
• Desflurane
• Enflurane
• Methoxyflurane

Question 3

What are these inhaled anaesthestics known as

Answer 3

Volatile anaesthetic agents

Question 4

How is the level of agent determined

Answer 4

by dial up vaporiser

Question 5

What do all inhaled anaesthetics cause some degree of

Answer 5

• respiratory depression

- cardiovascular depression

Question 6

Do inhaled anaesthetics provide analgesia?

Answer 6

no

Question 7

What are the two most commonly used inhaled anaesthetics

Answer 7

Isoflurane and Sevoflurane

Question 8

Name the two carrier gasses?

Answer 8

Oxygen, Nitrous oxide, Carbon dioxide

Question 9

What cylinder is oxygen kept in?

Answer 9

Black cylinders with white shoulders

Question 10

What are 3 uses of oxygen

Answer 10

• 100% given to animals with anaemia, pulmonary pathology, hypoventilation, animals recovering from N2O anaesthesia/ supplied during recovery if needed
• Used operatively routinely
• Used pre-operatively if you think intubation will be difficult e.g. brachycephalics
• Post operatively

Question 11

Name a benefit of oxygen?

Answer 11

• Does not depress ventilation
• Does not cause toxic nervous changes
• Does not cause toxic pulmonary changes
• Can be combined with nitrous oxide

Question 12

How is nitrous oxide delivered?

Answer 12

from compressed air tanks

Question 13

What is nitrous oxide combined with

Answer 13

oxygen

Question 14

What % of concentration will provide analgesic effects?

Answer 14

20%

Question 15

What % is nitrous oxide usually delivered at?

Answer 15

66% (33% oxygen)

Question 16

What is the ratio of nitrous oxide to oxygen in non-rebreathing circuits?

Answer 16

2:1

Question 17

What is the ratio of nitrous oxide to oxygen in rebreathing circuits?

Answer 17

1:1

Question 18

Why can the use of nitrous oxide cause the anaesthetic sparing effect

Answer 18

if delivered at 66% then lowers need for high volatile agent levels

Question 19

With what inhaled anaesthetic does nitrous oxide have a second gas effect?

Answer 19

Halothane

Question 20

What cylinders do N2O come in?

Answer 20

Blue

Question 21

What must you do once N20 is switched off?

Answer 21

oxygenate patient

Question 22

Name 3 negatives with nitrous oxide?

Answer 22

• not to use more than 80% (will lower oxygen below normal levels and patient will go hypoxic)
• Hypoxia
• N20 diffuses into gas-filled spaces and accumulates
• Do not use in bowel obstruction
• Do not use in middle ear disease
• Delivering nitrous oxide with pneumothorax can double the size of the pneumothorax in 10 minutes

Question 23

When might hypoxia occur? And how do you avoid it

Answer 23

if animal is breathing room air - as room air contains high levels of nitrogen
Avoid it by giving al patients 5-10 minutes of pure oxygen once N2O is switched off

Question 24

What piece of equipment should you use if concerned about hypoxia?

Answer 24

Pulse oximeter

Question 25

What cylinder is carbon dioxide in?

Answer 25

grey

Question 26

When is co2 used?

Answer 26

if patient is hypo-capnic

Question 27

At what level is co2 used?

Answer 27

4%

Question 28

Name 3 advantages of inhalational anaesthetics over injectable anaesthetics?

Answer 28

- depth of anaesthesia readily altered - Concentration of anaesthetic in blood or brain may be altered rapidly by changing vaporiser setting - Elimination of inhaled agents occurs mainly via the lungs therefore advantage of liver/kidney patient - Allows constant delivery of oxygen alongside agent - Most patients are intubated therefore IPPV may be performed and anaesthetic is 'safe' - Delivered to the lungs and then goes very quickly across the blood brain barrier to the brain and into the CNS

Question 29

Name 3 disadvantages of using inhaled anaesthesia over injectable anaesthesia?

Answer 29

- need for anaesthetic machine and range of equipment (costly) - Hazards, personnel risk, explosion risk - Knowledge required of circuits and machine - Induction and recover possibly delyaed due to lung pathology (not great induction agents) - Only alternative is IV total anaesthesia

Question 30

What is MAC

Answer 30

minimum alveolar concentration = measure of the anaesthetic potency

Question 31

How is MAC measured

Answer 31

it is the quantity of anaesthetic required to immobilize 50% of patients

Question 32

Are MAC's with a lower or higher number more potent?

Answer 32

lower MAC numbers are stronger and more potent

Question 33

What is blood gas solubility?

Answer 33

how soluble the gas is into the blood which then gets soaked up by blood and forms a reservoir in plasma - making it more difficult to pass through alveoli and pass the blood brain barrier

Question 34

Are more soluble or less blood gas soluble agents better? And why?

Answer 34

Low, they tend to have a more rapid induction and recovery

Question 35

Name an inhalational anaesthetic with low blood gas solubility

Answer 35

Sevoflurane

Question 36

Name an inhalation anaesthetic with high blood gas solubility

Answer 36

Halothane

Question 37

Which is more soluble: isoflurane or sevoflurane?

Answer 37

Isoflurane

Question 38

Which popular inhalational anaesthetic has a pungent smell?

Answer 38

Isoflurane

Question 39

Name 3 benefits of Isoflurane?

Answer 39

- relatively fast induction and recovery in comparison to Halothane - Good muscle relaxation - Fast recovery - Does not sensitise the heart to arrhythmias - Dose dependent - Licensed for variety of species - Greater safety margin than Halothane

Question 40

Name 3 negatives with Isoflurane?

Answer 40

- Not as fast induction or recovery as Sevoflurane - Transient excitability especially following painful surgery - Hypotension can occur due to CVS depression - Potent respiratory depressant - Poorly tolerated for mask induction due to smell - Not good analgesic on its own

Question 41

Name 4 characteristics of Sevoflurane

Answer 41

- Rapid induction and recovery in comparison to Isoflurane - Lower blood gas solubility than Iso - Odourless / pleasant non-irritant odour - Unstable in presence soda lime - More expensive than Iso - Can be used for mask induction - Non-irritant to airways - Can be used on exotics

Question 42

What happens when Sevoflurane is in the presence of soda lime

Answer 42

- Unstable - Degrades producing toxic metabolites (compound A which is proven to produce renal pathology in rats though not reported in small animals)