premedication

Question 1

What is premedication?

Answer 1

the provision of sedation & anxiolysis before induction of anaesthesia

Question 2

What are the benefits of premedication?

Answer 2

Reduction of dose of induction agent
Reduction of dose of maintenance agent
Provide pre-emptive analgesia & preventive analgesia
Ensure a smooth recovery
Prevent side effects associated with other anaesthetic drugs
Premedication/sedation can start at home (anxious/fearful animals)

Question 3

What is pre-emptive analgesia?

Answer 3

the administration of analgesic drugs prior to the onset of noxious stimulation which has the potential to be more efficacious

Question 4

What is the function of pre-emptive analgesia?

Answer 4

Reduced immediate post-op pain
Lowers the intensity and duration of subsequent pain
makes pain easier to control because it helps prevent the nervous system from becoming overly sensitive to pain (reduces peripheral and central sensitisation to pain)

Question 5

What is multimodal analgesia?

Answer 5

combining different analgesics acting by different mechanisms or at different sites in the nervous system

Question 6

What is the purpose of multimodal analgesia?

Answer 6

Additive and improved analgesia
minimises overall side effects by reducing dose of each drug

Question 7

What is preventive analgesia?

Answer 7

combines multimodal and pre-emptive concepts but continues into the early post-operative period

Question 8

What species is acepromazine (a phenothiazine) used as a premed for?

Answer 8

dogs
cats
horses

Question 9

What is neuroleptanalgesia?

Answer 9

a state of sedation and analgesia induced by combining neuroleptic and opioid analgesics

Question 10

What are the common drugs used to produce neuroleptanalgesia?

Answer 10

Phenothiazine agents
a2-adrenoceptor agonists
opioid analgesics

Question 11

How does acepromazine provide sedation?

Answer 11

interferes with dopamine transmission

Question 12

What are the contraindications of acepromazine?

Answer 12

Acepromazine causes a reduction in oxygen delivery to tissues via a reduction in haemoglobin concentration, caused by splenic sequestration of red blood cells therefore, it is not advised to administer acepromazine to patients with anaemia.

Question 13

Why must acepromazine be used in conjunction with other drugs?

Answer 13

does not have antinociceptive or analgesic properties

Question 14

What are the routes of administration of acepromazine?

Answer 14

SC
IM
IV
oral

Question 15

What are the adverse effects of acepromazine?

Answer 15

reduced BP
reduced oxygen delivery to tissues

Question 16

Give examples of alpha 2 agonists used as premedication in small animals

Answer 16

Medetomidine
dexmedetomidine (preferred)

Question 17

Give examples of alpha 2 agonists used as premedication in horses

Answer 17

Xylazine
detomidine
romifidine

Question 18

Give examples of alpha 2 agonists used as premedication in cattle

Answer 18

Xylazine
detomidine

Question 19

How do alpha 2 agonists cause sedation?

Answer 19

Inhibit adenylyl cyclase => reduces levels of cyclic adenosine monophosphate => hyperpolarisation of noradrenergic neurons
As cyclic adenosine monophosphate is inhibited, potassium efflux through calcium-activated channels prevents Ca ions from entering the nerve terminal => suppressed neural firing => inhibit norepinephrine release => reduces activity of ascending noradrenergic pathways => hypnosis and sedation

Question 20

How do alpha 2 agonists cause analgesia?

Answer 20

Stimulation of a-2 receptors in the dorsal horn of the spinal column => inhibits nociceptive neurons and reduces the release of substance P => analgesia

Question 21

What are the side effects of alpha 2 agonists?

Answer 21

profound cardiovascular effects and reduced cardiac output
Increased urine output
miosis (pupil constriction), decreased intraocular pressure and decreased ciliary body perfusion
vomiting

Question 22

What drug is the antagonist of alpha 2 agonists?

Answer 22

atipamezole

Question 23

Give examples of benzodiazepines used as premeds

Answer 23

Midazolam
diazepam
zolazepam
alprazolam

Question 24

What are the effects of benzodiazepines?

Answer 24

anxiolytic (reduces anxiety)
Muscle relaxation
Cardiovascular system stability
No analgesia

Question 25

What animals should benzodiazepines be used in?

Answer 25

ASA 3-5 Not healthy animals (causes excitement)

Question 26

What is the antagonist of benzodiazepines?

Answer 26

flumazenil

Question 27

What drugs should benzodiazepines be combined with for premedication?

Answer 27

opioids or ketamine or alfaxalone

Question 28

What is the drawback of using alfaxalone in large animals?

Answer 28

Large volume given IM can be painful

Question 29

What is the function of opioids in premedication?

Answer 29

provide pre-emptive (and preventive) analgesia synergism with sedatives

Question 30

Describe the sedative effects of opioids

Answer 30

ASA 1+2 - mild sedation when given alone ASA 3-5 - more profound

Question 31

Give examples of different opioids

Answer 31

Butorphanol, buprenorphine (partial agonists - lower analgesic effect) Methadone, fentanyl, morphine, pethidine (pure agonists)

Question 32

Describe the regulation of opioids

Answer 32

Schedule 2 controlled drugs

Question 33

What species can morphine be used in?

Answer 33

horse cat dog

Question 34

What is the route of administration of morphine?

Answer 34

IM SC Slow IV

Question 35

What is the duration of effect of morphine?

Answer 35

dog - 4hrs cat - 6-8hrs

Question 36

What receptors does morphine act on?

Answer 36

Full MOR agonist

Question 37

What are the side effects/considerations of morphine?

Answer 37

Vomiting Histamine release

Question 38

What are the target species of methadone?

Answer 38

horse cat dog

Question 39

What are the routes of administration of methadone?

Answer 39

IM SC Slow IV

Question 40

What is the duration of effect of methadone?

Answer 40

~4hrs

Question 41

What type of receptors does methadone act on?

Answer 41

Full MOR agonist NMDA antagonist NRI (noradrenaline uptake inhibitor)

Question 42

What are the considerations of methadone?

Answer 42

high licensed doses

Question 43

What are the target species for fentanyl?

Answer 43

dog cat

Question 44

What are the routes of administration of fentanyl?

Answer 44

IV IM

Question 45

What is the duration of effect of fentanyl?

Answer 45

0.3hrs

Question 46

What type of receptor does fentanyl act on?

Answer 46

Full MOR agonist

Question 47

What are the side effects of fentanyl?

Answer 47

Decreased HR Decreased RR

Question 48

What are the target species of butorphanol?

Answer 48

horse dog cat

Question 49

What are the routes of administration of butorphanol?

Answer 49

IM IV SC

Question 50

What is the duration of effect of butorphanol?

Answer 50

0.75-1hrs

Question 51

What receptors does butorphanol act on?

Answer 51

KOR agonist MOR antagonist

Question 52

What are the relative effects of butorphanol?

Answer 52

limited analgesia Good sedation

Question 53

What are the target species of buprenorphine?

Answer 53

horse cat dog

Question 54

What are the routes of administration of buprenorphine?

Answer 54

IM IV SC

Question 55

What is the duration of effect of buprenorphine?

Answer 55

6-8hrs Slow onset

Question 56

What types of receptors does buprenorphine act on?

Answer 56

Partial MOR agonist KOR antagonist

Question 57

Where are opioid receptors found?

Answer 57

Throughout the CNS in somatic and visceral sensory neurons (throughout the brain and dorsal horn of the spinal cord) and in the periphery (especially after inflammation)

Question 58

What types of opioid receptors are there?

Answer 58

MOR - mu opioid receptors KOR - kappa opioid receptors beta-receptors

Question 59

What is the effect of activation of MORs?

Answer 59

produces supraspinal and spinal analgesia euphoria sedation miosis (e.g. dogs) mydriasis (e.g. cats) respiratory depression decreased gastrointestinal motility due to inhibition of acetylcholine (ACh).

Question 60

What is the effect of KOR activation?

Answer 60

spinal and supraspinal analgesia mild sedation dysphoria diuresis miosis

Question 61

What is the effect of beta opioid receptor activation?

Answer 61

spinal and supraspinal analgesia cardiovascular depression.

Question 62

Give examples of other drugs possibly given before anaesthesia

Answer 62

anticholinergics antihistamines H2 receptor antagonists + gastroprotectants (brachy?) Anti-nausea/vomiting medication and NK1 antagonism Lidocaine Steroids or NSAIDs Antibiotics

Question 63

What premedication should be given to a ASA1 animal?

Answer 63

Acepromazine or alpha 2 agonist + opioid

Question 64

Describe premedication of ASA 2 animals

Answer 64

Low dose ACP/alpha 2 and opioid usually tolerated Care with ACP in liver disease Care with alpha 2 agonists in CVS disease - ACP may be a better option Alpha 2 agonists may be of use in HCM - hypertrophic cardiomyopathy (low dose)

Question 65

Describe pre-medication of ASA 3-5 animals

Answer 65

Avoid the alpha 2 agonists in compromised animals V low doses of alpha 2 agonist may be used if animal very distressed Opioid alone may be sufficient to sedate patient (but patients are often quiet/compromised) e.g. methadone or butorphanol Fentanyl and midazolam (IV) useful Ketamine and midazolam (IM or IV) cats (not in HCM) Alfaxalone and opioid is an option (volume of injectate is disadvantage), can add BZD too if necessary

Question 66

Describe the premedication of aggressive patients

Answer 66

Alpha 2 agonists alone (even high doses) often insufficient to sedate these animals Alpha 2 + ketamine + opioid (+/- acepromazine) combination IM

Question 67

What premedication can be given at home for aggressive patients?

Answer 67

‘Chill’ protocol (Gabapentin + trazodone or melatonin oral day before and morning of consult, and oral (injectable ACP) or oral transmucosal alpha 2 on arrival) Alprazolam or diazepam