Reproductive Anaesthesia

Question 1

What is the most likely reason for anaesthesia in SA?

Answer 1

• Neutering is one of the commonest elective SA surgical procedures you will perform – and anaesthesia is necessary
• Anaesthesia for C section & pyometra are commonest SA emergency procedures you will perform

Question 2

What are the aims of premedication?

Answer 2

–Sedation and anxiolysis facilitating handling of the animal

–Reduction of the stress for the animal

–Reduction the amount of other anaesthetic agents

–Provision of a balanced anaesthesia technique

–Provision of analgesia

–Counter the effects of other anaesthetic agents to be administered during the anaesthesia procedure e.g. atropine to prevent an opioid mediated bradycardia

–Contribute to a smooth, quiet recovery after anaesthesia

Question 3

What are some things you should consider and things you should do/not do with regards to premedication?

Answer 3

• Premedication is a vital component of most anaesthetics
• Premedication will affect the characteristics of the ensuing anaesthetic
• However the premed should always be tailored to the individual animal
• NB ‘Quad’ and ‘Triple’ cat combinations don’t have a ‘premed’ per se (all drugs given together)
• Do not premedicate all animals at the time of admission to the clinic – time premedication with expected peak drug effect relative to the estimated time of induction of anaesthesia
• Record the premedication drugs and dose on the animal’s anaesthesia record chart on the front of the cage
• Choose intramuscular administration of drugs over the subcutaneous route (except maybe rabbits?)
• Dose drugs based on lean bodyweight rather than obese weight
• Reduce drug dose in giant breed dogs to allow for the effects of metabolic body size
• Some premed type drugs in the total IM combinations and these have characteristics that make the surgery and anaesthesia more pleasant for patient and us!

Question 4

What kind of drugs are alpha 2 agonists?

Answer 4

Potent sedative and analgesic drugs

Question 5

Which alpha 2 agonists are used in SA mostly these days? What has superseded what?

Answer 5

•Xylazine was first a2 agonist to be used in practice – has been superseded by medetomidine and dexmedetomidine in SA

–Superseded by medetomidine & dexmedetomidine (cats & dogs)

•The superior selectivity of dexmedetomidine makes it the theoretical a2 agonist of choice for use in small animals…..?? EBM ??

–Dexmedetomidine – just have the active isomer present – medetomidine has an active and an inactive isomer present

Question 6

Which alpha 2 agonist are used in horses and cattle?

Answer 6

• Xylazine, detomidine and romifidine used in horses
• Xylazine and detomidine used in cattle (small rums sensitive)

Question 7

What other drugs can be used to mean that the dose of alpha 2 agonist can be reduced?

Answer 7

Synergism between a2 agonists and opioids or benzodiazepines means that the dose of the alpha 2 can be reduced

Question 8

Where do alpha 2 agonists provide good analgesia?

What is its duration of analgesia

Answer 8

• Alpha 2 agonists provide good analgesia through an agonist effect at spinal cord a2 receptors
• The duration of analgesia provided by a 10 µg/kg dose of dexmedetomidine is approximately 1 hour
• Intra-op analgesia improved

Question 9

What kind of effect do alpha 2 agonists have on ABP?

What about HR?

What about CO?

Answer 9

• a2 agonist cause biphasic effect on ABP (initial increase followed by a return to normal or slightly below normal values)
• HR is decreased throughout the period of a2 agonist admin (HR 45-60bpm dogs and 100-120 bpm cats)
• a2 agonist cause a reduction in cardiac output - not associated with a reduced oxygen delivery to CNS, heart, kidney & brain

Question 10

What effects does alpha 2 agonists have on respiratory systemi in healthy animals?

Answer 10

•Minimal effects on the resp system in healthy animals

–But if they are compromised, it can cause trouble!

Question 11

What happens to urine production when giving an animal alpha 2 agonists?

When do we need to be careful?

Answer 11

•Urine production is increased due to a reduction in vasopressin and renin secretion

–Can be a problem in a blocked cat – if we need to use an alpha 2, need to do cystocentesis straight away to relieve the bladder

–Can also be a problem with standing horses and skating on it and also sterility etc.

Question 12

What can reverse alpha 2 agonists with?

What does this mean?

Answer 12

a2 sedation and analgesia rapidly reversed by atipamezole,

Means analgesia is reversed also!!!

Question 13

What kind if reversal does IV and IM atipamezole give?

What should we remember to do?

Answer 13

• Reversal is advantageous because the recovery period is noted to be a high risk time for anaesthetic complications
• IM atipamezole produces smooth and good quality recoveries
• IV atipamezole produces a very rapid, excitable recovery from anaesthesia and this route of administration is not recommended
• It is important to ensure that analgesia is supplemented with different classes of drugs
• Atipamazole rarely used in horses and cattle

–Reserve it more for SA anaesthetics

–YOU DO NOT HAVE TO GIVE IT – YOU CAN LET THE ANIMAL BECOME CONSCIOUS AT A SLOWER RATE! DO NOT HAVE TO REVERSE AN ALPHA 2 AGONIST, THERE IS JUST THE OPTION

Question 14

Name the most common phenothiazine that is used?

Answer 14

Acepromazine commonest/only licensed one

Question 15

What effect does phenothiazines have? e.g Acepromazine

How can sedation be improved with this?

Answer 15

• Sedation and anxiolysis that is initially dose dependent
• With larger doses the duration of action is more prolonged
• The quality and reliability of sedation can be improved by combination with an opioid (neuroleptanalgesia)

Question 16

Is acepromazine (a phenothiazine) analgesic?

If yes, how long for and if not - what should we do?

Answer 16

Addition of an opioid also provides analgesia, advantageous since acepromazine itself is not analgesic

Question 17

How should we maximise sedation with phenothiazines?

Answer 17

• To maximise sedation the animal should be left undisturbed for 30-40 minutes after administration
• Less reliable sedation cf dexmedetomidine

Question 18

Which species and breeds should we avoid/be careful with useing phenothiazines in (e.g. acepromazine)?

Answer 18

• No evidence to suggest that acepromazine alters seizure threshold
• Giant breeds of dog may be “more sensitive” to the effects of acepromazine
• Some boxer dogs are sensitive to even small doses of acepromazine, which has been attributed to acepromazine induced orthostatic hypotension or vasovagal syncope in this breed

–Can make them faint

•Although acepromazine is not contraindicated in boxers, it is not the premedicant of choice in this breed - a very low dose (≤0.01 mg/kg) is recommended and animals should be monitored carefully after administration

Question 19

What kind of antagonist are phenothiazines (e.g. acepromazine)?

Answer 19

Acepromazine is a dopamine antagonist

Question 20

Which horses is phenothiazines (e.g. acepromazine) contraindicated in and why?

Answer 20

• Contraindicated in breeding stallions (see notes below)
• Do not administer to breeding stallions. Paralysis of the retractor penis muscle has been associated with the use of parenterally administered acepromazine in horses.

–Acepromazine has caused paraphimosis sometimes as a sequel to priapism. When extrusion of the penis occurs, the owner should be advised to inform his veterinary surgeon if retraction of the penis does not take place within 2–3 hours. Suitable treatments have been described in the veterinary literature e.g. manual compression during the period of general anaesthesia, penile support and manual compression, use of an Esmarch bandage, or drug reversal (e.g. slow intravenous administration of benztropine mesylate). When administered to male horses (geldings or stallions), use the lowest dose recommended to produce the required effect.

Question 21

Name some benzodiazepines?

Answer 21

Midazolam or diazepam (not licensed yet..)

Question 22

What kind of sedation do you get with benzodiazepines (midazolam or diazepam) in healthy cats and dogs?

Answer 22

• Benzodiazepines alone produce minimal or no sedation in healthy cats and dogs
• May even cause excitation due to loss of learned “inhibitory” behaviour
• Benzodiazepines are therefore given in combination with other sedatives

Question 23

What are benzodiazepines (midazolam or diazepam) often combined with in dogs?

What about cats?

Answer 23

• In dogs benzodiazepines often combined with opioids because both classes of drugs are cardiovascularly stable and the combination can provide reliable sedation
• In cats benzodiazepine and opioid is not very sedative, so benzodiazepine is most commonly combined with ketamine

Question 24

Name some options for drug combinations for premedication

Answer 24

• Acepromazine + opioid
• a2 agonist + opioid
• a2 agonist + BZD
• a2 agonist + Ketamine
• BZD + Ketamine
• Opioid + BZD
• a2 agonist + BZD + opioid

Question 25

Briefly describe the ASA categories

Answer 25

ASA 1: Healthy animal, elective procedure

ASA 2: Animal with systemic disease, not exhibiting clinical signs e.g. animal with a grade II heart murmur with no signs of exercise intolerance, change in pulse quality or rate

ASA 3: Animal with systemic disease causing mild clinical signs, or an animal with a systemic disease that is well stabilized on medication

ASA 4: Animal with systemic disease causing clinical signs e.g. a patient with an intestinal foreign body that is causing signs of sepsis

ASA 5: Animal that is not expected to survive e.g. a dog presented with a GDV that has severe haemodynamic compromise

ASA 6: Brain dead (organ harvest in humans)

Emergency procedures should also be noted (associated with increased anaesthetic risk)

Question 26

What premedication combinations are acceptible for an ASA 1 dog?

Answer 26

Usually determined by personality and the wellness of the animal

Question 27

What premedication combinations are acceptible for an ASA 2 dog?

Answer 27

ASA 2: Animal with systemic disease, not exhibiting clinical signs e.g. animal with a grade II heart murmur with no signs of exercise intolerance, change in pulse quality or rate

• Want to move away from reliance from alpha 2 agonist as they get sicker
• Acepromazine + Opioid combination
• It may be appropriate to use (dex)medetomidine
• Depends on the underlying reason for classification as ASA 2
• If ASA 2 is not assigned because of a disease that affects cardiovascular system or liver function-can use dexmedetomidine

Question 28

What premedication combinations are acceptible for an ASA 1 cat?

Answer 28

• The profound sedation caused by dexmedetomidine can be advantageous in cats
• IV access after light sedation e.g after acepromazine may be difficult to achieve
• Reversibility
• Alpha 2 very useful, great profound sedation – moving away in cats from acepromazine based protocols

Question 29

What premedication combinations are acceptible for an ASA 2 cat?

Answer 29

• Acepromazine + Opioid
• It may be appropriate to use dexmedetomidine
• Ask yourself what is the underlying reason for classification as ASA 2?
• If ASA 2 is not assigned because of a disease that affects cardiovascular system or liver function-can use dexmedetomidine

Question 30

Describe the time to peak sedation, duration of action, reversibilty and analgesic properties for all the well known premedicants in dogs and cats

Answer 30

Question 31

What are the 3 most commonly used induction agents?

Answer 31

–Propofol

–Alfaxalone

–Ketamine

Question 32

What kind of anaesthetic is ketamine?

Answer 32

Dissociative anaesthesia

Question 33

What is the benefi of using ketamine?

Answer 33

causes minimal cardiopulmonary depression

Question 34

What is ketamine often used with and why?

Answer 34

It can be used alone, although muscle relaxation is improved when it is combined with other sedative agents.

Question 35

What is the analgesia properties of ketamine?

Answer 35

Ketamine provide smild visceral analgesia and good somatic analgesia.

Question 36

How can we administer ketamine?

Answer 36

IV or IM

Question 37

What is zoletil?

Answer 37

tiletamine (ketamine derivative) and zolazepam (BZD)

Question 38

What is the anaesthesia properties of Zoletil (tiletamine (ketamine derivative) and zolazepam (BZD))?

Answer 38

•45-60 minute profound sedative anaesthesia

Question 39

When is zoletil used most?

Answer 39

In zoos

Question 40

What gases can we use to maintain anaesthesia in dogs and cats?

Answer 40

Isoflurane

Sevoflurance

Question 41

What are the possible IM combos for GA in CATS? (7)

Answer 41

Note: Ketamine alone is an old thing as it causes them to become rigid and twitch

Question 42

What are the IM combos for GA in DOGS? (3)

Answer 42

Note: Dogs tend to be more reliant on IV instead

Question 43

What is the problem of analgesia in horses?

Answer 43

Equine is a way behind in approving analgesia

Equine NSAIDs – renixin etc.

SA – more selective e.g. meloxicam etc.

Horses are hard to assess pain; they hide pain!

Horses have different distribution of pain receptors in brain and spinal cord so for example they don’t respond the same as dogs to methadone

Must give a multi modal approach!

Castrae – A2, reuce recumbency – ketamine, give LA, give NSAIDs

Still not doing as well as we could

Question 44

What are the problems of analgesia in cows?

Answer 44

Furthest behind!!!

We now have meloxicam… But some vets still are yet to use analgesia for castrates