Induction

Question 1

Describe the ideal injectable induction agent

Answer 1

Water soluble
Long shelf life
Stable when exposed to light
Small volume required
No local toxicity
No effect on vital organ function
Minimal individual variation
Safe therapeutic ratio
Onset – one vein to brain circulation time
Short duration of action
Non toxic metabolites
No histamine release

Question 2

Describe the pharmacokinetics and dynamics of Propofol (include time and vd)

Answer 2

Rapid onset of action -rapid uptake by CNS
Short period of unconsciousness (5-8 mins)
Large volume of distribution (lipophilic)
Rapid smooth emergence due to redistribution & efficient metabolism (hepatic and extra hepatic) metabolites inactive

Question 3

Describe the actions of Propofol on the patient

Answer 3

Respiratory depression (apnoea) - IPPV – can be affected by speed of admin – go slowly
Cardiovascular depression
Rapid and smooth recovery
Suitable for top ups or TIVA
Muscle relaxation usually ok
Anticonvulsant

Question 4

When is the use of propofol contraindicated?

Answer 4

Avoid in shock or sepsis

Decrease dose in old dogs

Question 5

What are the side effects of propofol?

Answer 5

Rigidity, twitching

Apnoea- Profound bradycardia

Question 6

Describe the action of Thiopentone sodium

Answer 6

Highly protein bound & displaced by other drugs e.g flunixin, phenylbutazone
Unionized fraction of the drug penetrates cells so pH can affect response
Plasma protein concentration also important
Crosses placenta
Metabolised in liver

Question 7

Describe the use of alfaxalone

Answer 7

Alfaxalone has a short plasma elimination half life and is cleared from the body relatively quickly
Alfaxalone can be give as repeated boluses or as TotalIntraVenousAnaesthetic to maintain anaesthesia
Premedication is preferable/essential in order to ensure a smooth recovery
Anaesthesia induction is smooth, and the injection is given slowly over 60 seconds.

Question 8

Describe the effects of sterious anaesthetics (e.g. alfaxalone) on the patient

Answer 8

Apnoea (temporary cessation of breathing during sleep) may be seen and IPPV may be necessary
The drug has good cardiovascular stability, causes no histamine release and produces good muscle relaxation
Animals should not be disturbed during recovery as excitement can occur

Question 9

Name a dissociative agent

Answer 9

Ketamine

Question 10

Give the uses of ketamine

Answer 10

Can be combined with BZD, alpha 2 agonists, acepromaine, opioids
Versatile induction agent
Invariably needs to be combined with something

Question 11

Describe the properties of ketamine

Answer 11

Rapid induction
Respiratory effects are mixed – bronchodilation and RR usually preserved but may stop!
GOOD ANALGESIA
CVS effects depend on dose
Muscle tone ↑ and jerky movements
Salivation and lacrimation ↑
Ketamine can be diluted with sterile water or physiological saline

Question 12

Describe the problems of using ketamine

Answer 12

Stormy recovery if disturbed or not adequately premedicated
Depth assessment is different (eyes open)
Corneal drying - use ‘Lacrilube’ or similar tears
Vomiting common with alpha 2 combinations avoid in patients with GI obstruction
Avoid in patients with ↑ ICP, ocular surgery, fever, hyperthyroids

Question 13

Describe the process of induction in equine patients

Answer 13

Usually an intravenous agent is used
After an induction agent a horse becomes unconscious
The quality of induction is affected by the premedication
Anaesthesia is then maintained by incremental ‘top ups’ IV or by infusion (TIVA) or by inhalation agents
Anaesthesia can be induced with inhalants in foals

Question 14

What can be the problems with using ketamine with horses

Answer 14

Must not be used alone (seizures)
Eyes remain open and central, less cumulative than thiopentone
Can be used as ‘top ups’ (don’t exceed induction dose)

Question 15

Describe the intubation process with ruminants

Answer 15

Small ruminants are intubated by direct visualisation
Larger ruminants are intubated by palpation
Use cuffed tubes
Regurgitation

Question 16

Describe the induction of anaesthesia in pigs (include drugs and potential problems)

Answer 16

Can be achieved with drugs given im (deep) on the neck near the ear, iv or via mask with inhalant
Ketamine, alfaxalone, propofol
Ketamine combinations
Malignant hyperthermia (rare condition of pigs will manifest itself soon after exposure to inhalant usually), rapidly fatal, can be treated with dantrolene

Question 17

What differences are there in bird prep and GI?

Answer 17

Have a reputation for high GA mortality, they hide illness well, IPPV a good idea
They have a high metabolism meaning conditions will change quickly
Stabilise bird pre op, don’t fast for too long. Raptors and waterfowl should be fasted for 4-6 hours to ensure crop is empty
Care with body position (ventrolateral recumbency is best), IPPV, types of ET tubes (birds have complete tracheal rings, Cole tubes useful)

Question 18

Describe the process of induction in birds

Answer 18

Most inductions are performed using an inhalant (e.g. isoflurane in oxygen)
Apnoea common, so intubation strongly recommended
Air sac cannulation is possible – air sac just behind the thigh

Question 19

What is it about reptiles that make them hard to induce /maintain using gas?

Answer 19

Blood shunting (many can go through periods where send blood to the lungs or will send more blood to kidneys) can make gas induction and/or maintenance difficult or even impossible
Chelonia especially difficult to induce with gas (may just stop breathing)
Heart rate often does not change even from deep anaesthetic plane to very much awake!

Question 20

Describe the process of inducing reptiles

Answer 20

Gas induction i.e. isoflurane or sevoflurane
Injectable i.e. propofol or alfaxalone
TIVA with alfaxalone works well in chelonia
Giant or fractious patients can be sedated with ketamine/midazolam or ketamine/medetomidine
Analgesia butorphanol +/- NSAID (buprenorphine in some too)
Intubation generally straight forward  chelonia can be difficult due to large, fleshy tongue
Glottis remains closed when not breathing