Anesthesia

Question 1

Classic aims of premedication: (4)

Answer 1

To relieve anxiety, apprehension, fear and resistance to anesthesia.

To counteract unwanted side effects of agents used in anesthesia.

To reduce the dose of anesthetic.

To contribute to perioperative analgesia.

Question 2

The main purpose for use of Anticholinergic agents: (3)

Answer 2

To reduce salivation and bronchial secretions.

To block the effects of impulses in the vagus nerves.

To block certain effects produced by drugs that stimulate the parasympathetic system.

Question 3

Atropine inhibits transmission of

Answer 3

postganglionic cholinergic nerve impulses to effector cells but inhibition is not equally effective all over the body.

Certain cerebral and medullary functions are initially stimulated then later depressed, the final outcome depends on the dose used and the route of administration.

Clinical doses may produce an initial slowing of the heart due to stimulation of vagal centers in the brain before its peripheral anticholinergic effects occur.

Question 4

Atropine has less effect upon? than upon what?

Answer 4

less effect upon the urinary bladder and intestines than upon the heart and salivary glands.

Question 5

Atropine effects on the heart rate:

Answer 5

initial slowing due to central action, after that increase (main effect) due to peripheral inhibition of the cardiac nervus vagus.

Question 6

Atropine effects on the pupil

Answer 6

mydriasis

Question 7

Atropine effect on the GI tract

Answer 7

Reduction of muscle tone in the gastrointestinal tract.

In horses, incidence of post-anesthetic colic may be increased.

Question 8

What should you note in regard to atropine and ketamine interaction?

Answer 8

Combined with ketamine, too high HR and heart rate! Use with care.

Question 9

Describe Glycopyrrolate’s effects.

Answer 9

Anticholinergic agent: Diminishes the flow of saliva, five times as potent as atropine.

Due to parasympatholytic properties, increases blood pressure.

A slower onset of action than atropine.

Dose in vet practice 0.01-0.02 mg/kg, no species-related pharmacokinetic disadvantages.

Might have less effect on vision, but still causes pupillary dilation in the cat (mydriasis).

Question 10

What group does acepromazine belong to?

Answer 10

belongs to tranquilizers,
phenothiazine group

Question 11

Name 2 anticholinergic premedications/intraoperative meds.

Answer 11

atropine
glycopyrrolate

Question 12

With increased doses of acepromazine, what occurs?

Answer 12

With low doses, there are effects on behavior.

With the increased dose sedation occurs, but the dose-response curve rapidly reaches a plateau.

Higher doses do not increase, but only lengthen sedation and increase side effects.

Further increase in doses may cause excitement and extrapyramidal signs (impaired motor control).

Question 13

In many animals, sedation with acepromazine IM may be achieved with doses of

Answer 13

IM doses 0.03mg/kg.

Although the acepromazine can be used at 10 times this dose for producing prolonged effect.

A calming effect can be seen even doses below 0.03 mg/kg.

Question 14

Central effects of acepromazine besides sedation: (3)

Answer 14

Hypothermia
Moderate antiemetic effect, especially against opioid-induced vomiting.
Causes a dose-related fall in blood pressure – vasodilation (Caution in hypovolemic animals!).

Clinical doses have little effect on respiration.
The effects on heart rate generally minimal, mostly a slight rise.

Question 15

Acepromazine effect on smooth muscle?

Answer 15

Acepromazine has a powerful spasmolytic effect on the gut (as well as vascular smooth muscle - vasodilation), is effective in treatment of equine spasmodic colic.

Question 16

Acepromazine effects on the heart:

Answer 16

Antiarrhythmic effects, protects against epinephrine-induced fibrillation.

The effects on heart rate generally minimal, mostly a slight rise.

In horses and dogs it significantly reduces the incidence of death associated with anesthesia and surgery.

It has been shown to be a free radical scavenger.

Question 17

Relative contraindications to the use of acepromazine: (6)

Answer 17

Hypovolemia (cause vasodilation)
Liver damage (increased duration of action)

Renal hypertension
Boxer dogs

Stallions, because of danger of priapism (prolonged erection)
Anemia (hypoxia risk)

Question 18

Time of onset of effects of acepromazine.

Answer 18

Sedation is obvious within 5 minutes, but 15-20 minutes should be allowed to elapse before general anesthetic agents are given.

Maximal effects are seen after 30-45 minutes after IM or SC injection.

Question 19

alfa2-adrenomimetics analgesic properties

Answer 19

They are potent analgesics both spinal and central actions.

Question 20

Alfa 2 Adrenomimetics’ Actions with clinical significance:
Central:
Analgesic:
Pituitary:
Central and peripheral:
Peripheral:

Answer 20

Central: sedation, depression of cardiovascular center, „late“ vasodilation (after peripheral vasoconstriction - biphasic response).

Analgesia: central and spinal.

Pituitary: reduced ADH (increased urination), reduced ACTH (decreased cortisol).

Central and peripheral: bradycardia

Peripheral: cardiovascular (vasoconstriction), intestinal relaxation, uterine stimulation, reduced renin and insulin secretion (hyperglycemia), platelet aggregation.

Question 21

Alfa2 receptor subtypes: (3)

Answer 21

alpha-2A,
alpha-2B,
alpha-2C

Question 22

Besides analgesia; the alpha-2A receptor promotes (5)

Answer 22

hypnosis, sedation,
inhibition of insulin secretion, neuroprotection, and sympatholysis.

Question 23

Alpha-2B receptors are involved in

Answer 23

spinal analgesia and vasoconstriction of peripheral arteries.

Question 24

Alpha-2C receptors are involved in

Answer 24

pain modulation, mood- and stimulant-induced locomotor activity, regulation of epinephrine outflow from the adrenal medulla, and modulation of cognition.

Question 25

Xylazine differences from the newer agents:

Answer 25

1. no imidazole ring in the structure, not active to imidazole receptors.
2. Horses, dogs and cats require 10 times the dose needed in cattle. Pigs are even more resistant.
3. Increased uterine contractions at equi-sedative doses, greater than for the newer agents. (contraindicated in late pregnancy?)

Used in IV, IM, rarely SC routes.

Question 26

Xylazine analgesic properties.

Answer 26

Potent analgesic, but additional analgesia must be used to support the effect.

Relatively safe, unless some serious collapses and deaths have been reported.

Question 27

Xylazine is particularly used in combination with

Answer 27

ketamine – it helps to reduce muscle rigididy caused by the dissociative agent.

Question 28

Describe detomidine.

Answer 28

An imidazole derivative, sedative/analgesic.
Can be given in IM, IV routes.

Used widely as a sedative and premedicant in horses, also in cattle, no big difference in doses, very often 10-30 microg/kg.

Effective analgesic in equine colic.

Difference from xylazine – in lower doses slows electrical activity in pregnant bovine uterus, in higher doses will increase it.

Question 29

Two advantages of detomidine over xylazine:

Answer 29

less stimulation of uterus, decreased likelihood of recumbency.

Question 30

Describe medetomidine.

Answer 30

An imidazole derivative, used mainly in small animals, but can be used in variety of species.

Induces sedation, hypnosis and analgesia, also bradycardia, arterial hypertension followed by hypotension and reduced cardiac output (biphasic response).

In most animals slows respiration.

Question 31

Medetomidine effects on uterine musculature.

Answer 31

In bitches, in lower doses (20 microg/kg) the electrical activity of uterine muscle is depressed, in higher (40-60 microg/kg ) doses increased.

Question 32

Medetomidine combinations with what are are more effective than the sedative alone? (2)

Answer 32

opioids or ketamine

Question 33

In wild animals, higher doses of medetomidine are required, usually in combination with

Answer 33

ketamine, administered by dart gun.

Medetomidine – ketamine combinations provide excellent immobilization and relaxation in a wide range of animal species.

Question 34

Describe dexmedetomidine.

Answer 34

S-enantiomer of medetomidine.

The most potent and specific alfa2-agonist available.

Used in dogs and cats in dose rates half of those used with medetomidine.

Less side effects? Many studies have found no clinically significant differences other than lower dose.

Question 35

Which is more potent medetomidine or dex?

Answer 35

dex is Used in dogs and cats in dose rates half of those used with medetomidine.

Question 36

New Alfa2-agonist, but not used for premedication:

Answer 36

tasipimidine, “Tessie”

Target species: dogs.

Short term alleviation of situational anxiety and fear in dogs triggered by noise or owner departure.

Question 37

Main opioid receptors: (3)

Answer 37

Main receptors are mu, kappa and delta.

Endogenous ligands endorphins, dynorphins and enkephalins are found in CNS and bind to opioid receptors.

Question 38

mu is found throughout..?

Answer 38

the CNS.

Question 39

The mu receptor is the main receptor responsible for

Answer 39

the analgesic action of opioids, but binding to mu is also responsible for the majority of opioid side effects, including euphoria and addiction in humans.

Question 40

Kappa receptors mediate

Answer 40

analgesia in addition to mu receptors, but kappa agonists are relatively weak analgesics.

Kappa may be responsible of dysphoria, it may also antagonize some side effects induced by mu.

Question 41

The delta receptor may modify the actions of

Answer 41

opioids at other receptors.

Question 42

Describe Opioids for premedication:

Answer 42

they have synergistic action with most sedatives and analgesic agents.

Opioids have anesthetic sparing effects (except in horses), allowing lower doses of injectable and inhalational agents, thus reducing side effects of these agents.

Question 43

Side effects of opioids: (4+)

Answer 43

vary with species and drug.

Respiratory depression is most common, mediated by mu receptor.

Vomiting in dogs and cats, caused by morphine.

Other possible side effects: bradycardia, hyperthermia, mydriasis or miosis dependent on species, pruritus, urinary retention, histamine release.

Question 44

Opioid Respiratory depression is most common side effect, mediated by what receptor.

Answer 44

mu

Question 45

Name 3 full mu-agonists.

Answer 45

morphine
fentanyl
methadone

Question 46

Describe morphine.

Answer 46

The „gold standard“ opioid, produces profound analgesia mediated via mu (and possibly kappa) agonist activity.

Produces euphoria and is addictive in humans.

Question 47

What is Etorphine?

Answer 47

very potent derivative of morphine (dangerous, even 1 drop transcutaneously!).

Not used in clinical practice, maybe in research in some countries.

Strong respiratory depressant.

Small volumes can be used in dart gun for immobilizing large wild animals. Extremely long-acting.

Antidote: diprenorphine, in humans naloxone.

Question 48

Describe fentanyl.

Answer 48

Pure mu agonist, potency around 100 times greater than morphine – can be used in small doses to produce profound analgesia.

Relatively potent respiratory depressant.

Bradycardia may occur with the use of high doses, but is rapidly reversible by reduction of the infusion rate or treatment with anticholinergics.

Question 49

Fentanyl onset and duration of action.

Answer 49

After IV injection rapid onset of action (1-2 minutes), but a single dose will only last around 20 min.

Question 50

Morphine onset and duration of action.

Answer 50

Onset time around 10-15 min after IV and up to 30 min after IM administration.

Most commonly administered every 4 hours in dogs and horses and every 4-6 hours in cats.

Question 51

Describe Methadone

Answer 51

Full mu agonist

Much less likely to induce vomiting and histamine release, safer for IV injection.

Used in cats and dogs.

Question 52

Methadone onset and duration of action.

Answer 52

approx. 30 min onset from IM injection?

Duration of action in dogs and cats 3-4 hours, in horses 4-8 hours.

Question 53

Name 2 partial mu agonists.

Answer 53

buprenorphine
butorphanol

Question 54

Describe buprenorphine dose-response curve.

Answer 54

has a „bell-shaped“ dose-response curve, initially, increasing the dose increases the analgesic effect until a threshold is reached, after which further dosing results in a decreasing analgesic effect.

Does not normally occur with clinical doses.

Question 55

Describe buprenorphine onset and duration of action.

Answer 55

Long onset of action, around 45 min, long duration of up to 6-8 hours.

Question 56

What receptors does butorphanol act on?

Answer 56

is a kappa-agonist and mu-antagonist

Does not produce profound analgesia, can be used in case of mild to moderate pain (debated by data!).

Question 57

Butorphanol onset and duration of action.

Answer 57

Onset time around 5-15 min, duration of action controversial, about 2 hours.

Question 58

Butorphanol can antagonize what full mu agonist?

Answer 58

morphine

Question 59

Name 2 mu antagonists.

Answer 59

naltrexone
naloxone

Question 60

Naloxone acts on what receptors?

Answer 60

antagonist at all opioid receptors, but less effective against partial agonists.

Question 61

Naltrexone is a

Answer 61

a mu-opioid receptor antagonist

long-acting derivative of naloxone

useful against long-acting pure agonist.

Question 62

Describe diazepam in vet med.

Answer 62

Major role in vet practice to control convulsions of any origin, but can cause paradoxical excitement.

For induction of anesthesia, its combination with opioids provides good cardiovascular stability.

Particularly useful prior to or in combination with ketamine to reduce hallucinations.

The sedative and hypnotic effects of diazepam alone appear to be minimal.

Used IV and rectally, many injection solutions irritant.

Question 63

Describe midazolam effects in adult healthy animals.

Answer 63

In adult healthy animals does not induce sedation, is an anxiolytic, however excitement reactions can occur.

In sick animals and in combination with opioids or ketamine good hypnosis can be achieved.

Amnesia.

Question 64

Which metabolizes propofol more slowly, dogs or cats?

Answer 64

cats

because of the inability to conjugate phenols, metabolizes propofol more slowly.

Question 65

Cardiac effects of propofol.

Answer 65

Propofol causes dose-dependent respiratory and cardiovascular depression.

decreases risk for catecholamine-induced cardiac arrhythmias.

Question 66

Do not use alfaxalone with

Answer 66

propofol!

Administration together with other injectable anesthetic agent is contraindicated.

Question 67

What portion of Ketamine binds in general

Answer 67

Binds to protein by approximately 50% (dogs and horses).

This makes ketamine a drug of choice for hypoproteinemic patients (with burns or blood loss).

Question 68

Ketamine is usually combined with

Answer 68

benzodiazepines and/or
alfa2-agonists in order to counteract the unwanted „dissociative“ side effects.

Question 69

Describe how tiletamine differs from ketamine.

Answer 69

twice as potent and much longer lasting.

Question 70

Buprenorphine affinity to what receptors

Answer 70

High affinity to mu receptors.

A large dose of morphine can displace buprenorphine from the mu receptors if more profound analgesia is required.

And, buprenorphine can displace the previously administered mu- opioid from the receptor, thus reducing the side effects (sedation and respiratory depression), but still produce opioid-related analgesia.