Clinical Inhalation Anaesthesia

Question 1

Inhalation anaesthetic agents are administered and removed via

Answer 1

the lungs by the ETT/face mask

Question 2

inhalation anaesthetics are distributed to

Answer 2

other tissues like the lungs, then to the brain where significant effects may occur

Question 3

inhalation anaesthetics produce

Answer 3

controlled, reversible intoxication of CNS

Question 4

inhalation anaesthetics have variable

Answer 4

metabolism in the body

Question 5

inhalation anaesthetics is used for

Answer 5

maintenance of anaesthesia

Question 6

What is MAC

Answer 6

• method of comparing potency of inhalational anaesthetics
• lower MAC of agent, the more potent it is
• lower dose needed to achieve similar effect
• minimum alveolar concentration at which 50% of patients do not respond to a supramaximal noxious stimuli (minimum conc in the alveoli of the anaesthetic that 50% of animals will NOT move during a painful procedure)

Question 7

What is the MAC of Isoflurane in a dog with no other drugs on board?

Answer 7

1.3%

Question 8

What is the MAC of sevoflurane in a dog with no other drugs on board?

Answer 8

2.3%

Question 9

MAC does NOT correlate with…

Answer 9

the vaporiser setting

Question 10

If the Et value is at MAC…

Answer 10

50% of patients will be too light

Question 11

if the ET value is > MAC

Answer 11

less likely the P is too light BUT some may be too deep & have negative effects of anesthetic agent (overdose)

Question 12

If the Et value is <MAC

Answer 12

many p’s will be too light OR other drugs used have a MAC sparing effect

Question 13

What factors impact MAC?

Answer 13

• sedatives/opioids/CRIs
• pregnancy
• PIVA, N2O
• BODY TEMP
• AGE
• severe anaemia
• hypo- or hypernatraemia
• species

Question 14

What are considered volatile inhaled anaesthetic agents?

Answer 14

isoflurane, sevoflurane, desflurane
Halothane

Question 15

What inhalant anaesthetic agents are gaseous?

Answer 15

Nitrous oxide

Question 16

What are some advantages of sevoflurane over isoflurane?

Answer 16

• faster speed of induction & less pungent than Isoflurane
• faster speed of recovery
• neuroanaesthesia (MRI, CSF tap, Brain Sx)

Question 17

What are MAC-sparing techniques?

Answer 17

Analgesia –> Local blocks, CRI

Question 18

CRI requires…

Answer 18

a syringe driver or infusion pump

Question 19

CRI may be used intra-op as part of …

Answer 19

maintenance technique to balance anaesthesia

Question 20

CRI may be continued Post-op

Answer 20

to provide analgesia for 24-72 hours

Question 21

CRI can also be used as an

Answer 21

intermittent bolus with plasma peaks & troughs in the plasma levels

Question 22

In CRI’s, often a loading dose is required because…

Answer 22

depending on the half-life of the drugs, it could take days to achieve steady plasma levels

Question 23

(Dex)medetomidine CRI intra-op is used to

Answer 23

reduce inhalant requirements & need sedation

Question 24

(Dex)medetomidine is used as a CRI post-op when…

Answer 24

mild sedation is required

Question 25

Ketamine CRI can be used in what species?

Answer 25

All species

Question 26

Ketamine CRI works at

Answer 26

the NMDA receptor to prevent/treat ‘wind-up’

Question 27

Ketamine CRI can be used for..

Answer 27

• pain poorly responsive to conventional techniques
• neuropathic pain
• chronic pain
• ketamine reduces opioid requirements

Question 28

What patients should you avoid ketamine CRI?

Answer 28

patients w/ head trauma

Question 29

Morphine & methadone CRI is used for…

Answer 29

intra-op instead of repeated bolus injections
for post-op analgesia

Question 30

Fentanyl CRI is used intra-op…

Answer 30

to provide efficient analgesia & reduce inhalant requirements

Question 31

what is one thing of note for a fentanyl CRI?

Answer 31

• Stop CRI at least 15-20 mins before end of anaesthesia, otherwise P will not recover quickly or breath normally

Question 32

A fentanyl CRI can be restarted if…

Answer 32

severe pain w/ careful consideration of dosing or if a local block was not possible or failed

Question 33

Lidocaine CRI reduces… and augments…

Answer 33

• reduces inhalant requirements
• augments analgesia produced by opioids

Question 34

Lidocaine CRI can be used in what species?

Answer 34

dogs & horses
NO CATS

Question 35

Lidocaine CRI can cause

Answer 35

CVS depression/hypotension
- in recovery, may result in mild sedation & nausea

Question 36

What are the options for maintenance of anaesthesia during major Sx?

Answer 36

• inhalant anaesthesia delivered in oxygen
• +/- opioids & other analgesics
• +/- local block PRN
• +/- CRI during Sx +/- post-op

Question 37

What are important points of Induction of analgesia w/ inhalant agents with a face mask or induction box?

Answer 37

• considerable atmospheric pollution
• poor control of anaesthetic depth
• no airway protection
• can be prolonged due to breath holding
• avoid if possible

Question 38

What is the process of using inhalation anaesthesia?

Answer 38

1. pre-anaesthetic assessment
2. premedication (IM/IV)
3. IV induction of anaesthesia
4. Intubate the trachea w/ ETT
5. secure ETT
6. turn on appropriate O2 flow
7. inflate cuff of ETT & leak test
8. turn on vaporizer
9. monitor depth of anaesthesia continually

After Sx:
10. turn vaporizer to zero, but leave O2 on for at least 5 mins
11. if circle: increase O2 flow
12. allow P to breathe 100% O2 for 5-10 mins
13. untie ETT
14. deflate cuff & extubate trachea only when swallowing reflex returns
15. provide O2 by face mask to prevent hypoxaemia until awake & normothermic