Induction

Question 0

Which inhalational agents can be used to induce anaesthesia?

Answer 0

• isoflurane
• sevoflurane
• halothane
• desflurane (not licensed)
• N20 (nitrous oxide)
• xenon (new, expensive, specialised equipment needed)

Question 1

Which injectable agents can be used to induce anaesthesia?

Answer 1

• propofol
• alfaxalone
• ketamine
  > thiopentone/thiopental (old, can’t get vet form anymore)
  > etomidate (not licensed, human drug)

Question 2

What is the most common route of induction?

Answer 2

IV

Question 3

What do GA agents cause?

Answer 3

Dose dependant CNS depression

• continuum from sedation -> anaesthesia
  eg. use of propofol as a sedative (michael jackson!)

Question 4

How is CV and respiratory system affected by anaesthetic agents?

Answer 4

> CV
- v CO
- vasodilation
- reduced BP 
- bad for kidneys etc. 
> resp
- v RR
- v TV (tidal volume)
= reduced minute volume
*dose-dependant*

Question 5

Do GA drugs provide analgesia?

Answer 5

No - so must administer analgesics eg. opioids

Question 6

What does uptake of GA depend on?

Answer 6

• route of administration

Question 7

What does distribution into tissues depend on?

Answer 7

• blood flow (eg. injecting into sublumbar fat)
• may be influenced by disease
• lowers blood levels if injected into muscle etc.

Question 8

Which species are particularly sensitive to a2 agonists?

Answer 8

Goats

Question 9

What is metabolism of drugs influenced by?

Answer 9

• Species
• Disease state (esp. liver and kidneys, lungs for inhalation agents)
  > thiopental in a thin dog will maintain for a long time due to lack of body fat

Question 10

How does propofol’s action differ in cats?

Answer 10

take a long time to recover
- enzyme lacking to conjugate glucuronides
- problems metabolising triglyceride lipid carrier of drug
> cumulative effects of the drug, can be TOXIC if given repeatedly
> Oxidative injury, Heinz body production, anaemia and death

Question 11

Where does the induction agent ultimately act?

Answer 11

In the brain

Question 12

How does age affect amount of induction agent required?

Answer 12

• extremes of age require less

Question 13

Should doses of GA drugs be learnt?

Answer 13

NO NOT FOR EXAMS!!! Know where to find them

Question 14

WHat type of drug is propofol? What is it’s appearance and ROA?

Answer 14

• a phenol
• white opaque liquid (rich medium for bacterial growth)
• must be given IV (not IM)

Question 15

What can propofol be used for?

Answer 15

Induction AND maintainence eg. if cannot use inhalation agents (TIVA)

Question 16

Pharmacodynamics of propofol

Answer 16

• rapid onset after injection
• blood levels v by redisribution
• rapid metabolism (hepatic and extra-hepatic eg. lungs)

Question 17

Effects of propofol

Answer 17

• CV depression (vasodilation and v BP)
• respiratory depression
  > so give SLOWLY over one minute

Question 18

What is propclear?

Answer 18

Nanodroplet clear solution - no longer available

- caused extreme pain on injection

Question 19

What is propofol plus?

Answer 19

Preservative (benzyl alcohol) means can be used once opened (doesnt have to be discarded on the day)
> benzyl alcohol toxicity ->
- prolonged recovery and hyperkinesia in cats
- tremors in dogs
* DO NOT USE FOR TIVA*

Question 20

What type of drug is alfaxalone? What s it mixed with in preparations?

Answer 20

steroid - poorly soluable

- mixed with solubilising agent (cyclodextrin)

Question 21

ROA alfaxolone?

Answer 21

IV or IM

Question 22

How does alfaxolone differ to propofol?

Answer 22

• rapid onset of action, short duration

- less CV and respiratory depression than propofol

Question 23

Potential side effects and cons of alfaxolone?

Answer 23

More expensive

Can see excitement on recovery if not adequately sedated

Question 24

What type of drug is ketamine?

Answer 24

- Dissociative anaesthetic | - Analgesic actions at sub-anaesthetic doses (NMDA receptors)

Question 25

ROA ketamine

Answer 25

IM or IV

Question 26

What can ketamine be used for?

Answer 26

Inuction and maintainence of anaesthesia

Question 27

Why is ketamine NEVER GIVEN ALONE?

Answer 27

Excitation and muscle tension if given alone, always requires a sedative (benzodiazepine or a2 ag) - also need to lubricate eyes as will remain open

Question 28

What situations is ketamine useful for?

Answer 28

- angry cats | - brachycephalic breeds

Question 29

What is the triple combination? Which species is this commonly used in?

Answer 29

``` - Aggressive cats > Ketamine, medetomidine, opioid - IM - onset of action ~5 mins - single injection alone suitable for short procedures ```

Question 30

Which species if ketamine commonly used in following sedation with a n a2 agonist?

Answer 30

Horses after PROFOUND sedation with an a2 ag | - given IV combination with a benzodiazepine (diazepam or midazolam)

Question 31

How does ketamine affect the CNS, CB and resp systems?

Answer 31

> CNS reflexes are preserved (palpebral, jaw tone, swallowing) > CV: SNS stimulated -> hypertension and tachycardia mildly, but some direct CV depression also > resp: mild resp depression

Question 32

Where is thiopental usually used nowadays?

Answer 32

Horses - not licensed for vet use anymore - used for induction (to effect) and as top up during maintainence

Question 33

Effects and potential side effects of thiopental?

Answer 33

- irritant and necrosis if administered extravascualrly (alkaline) - CV and resp depression similar to propofol

Question 34

Can thiopental be used once vial is opened?

Answer 34

Yes for ~5d (pH so high nothing can grow)

Question 35

What drug or drug combination is best for high risk, sick patients? POtential problem with this drug?

Answer 35

*Etomidate - minimal CV and resp depression - problem: depresses adrenal gland function and cortisol production > NOT LICENSED * Fentanyl/midazolam combination - very potent opioid

Question 36

Which inhalational agents are used for induction? Why would these be used over injectables?

Answer 36

- sevoflurane or ioflurance delivered in oxygen | > aggressive patients if IV impossible

Question 37

What are the downsides to inhalational indcution?

Answer 37

- ^ risk pollution and personnel exposure | - may see excitement/stress during induction

Question 38

Which inhalational agent is more irritating to respiratory passages and what effect may this have?

Answer 38

Isoflurane -> breath holding (but is cheaper)

Question 39

How can the smell of isoflurane be disguised to prevent mask avoidance?

Answer 39

Smear food inside mask

Question 40

What concentration roughly approximates brain concentration of anaesthetic drug?

Answer 40

ALveolar concentration

Question 41

What does partial pressure mean?

Answer 41

Amount in blood

Question 42

If an agent is very soluble in blood how is the partial pressure or tension of gas in the brain affected?

Answer 42

Lower in brain (doesnt ant to leave blood!)

Question 43

What is the partition coefficient?

Answer 43

Blood:Gas partition coefficient = no. particles gas in blood vs. alveolus - high number means gas is very soluble in blood (and therefore induction and recovery will take longer, as moving agent from blood to brain and back takes long time) - eg. halothane 2.4 [long induction and recovery], N2O and desflurane ~0.4 [short induction and recovery]

Question 44

Why is endotracheal intubation advocated?

Answer 44

- o2 delivery - inhalational anaesthetic if required - protect airway from occlusion or aspiration - allow ventilation to be supported if depressed