Injectable Drugs Used in Anesthesia: Preanesthetic Medications

Question 1

Please read the first scenario in the questions.
You are going to administer the alpha-2 adrenergic agonist, xylazine, to this colt as a premed. Which of the following scenarios regarding this drug is the most accurate?
A. The drug will cause peripheral vasoconstriction and bradycardia.
B. The drug’s beta receptor activity will increase blood pressure by improving cardiac contractility and heart rate.
C. Xylazine is a DEA Class II controlled substance.
D. Alpha-2 adrenergic agonists are safe drugs to use on emergency cases because they have minimal cardiovascular adverse effects and they are reversible.
E. All of the above statements are accurate.

Answer 1

The drug will cause peripheral vasoconstriction and bradycardia

Question 2

Please read the first scenario in the questions.
After your preanesthetic medication produces adequate sedation, the owner mentions she read on the internet that inducing the colt to anesthesia using isoflurane and a face mask is the safest anesthesia for Arabian colts. Is this a good idea?

Answer 2

No, isoflurane is very pungent, so animals do not tolerate its odor well for mask induction

Question 3

You need to anesthetize a very active and nervous 6-month old Italian greyhound for an elective castration. Physical examination and lab data reveal a healthy dog.
What preanesthetic medication choices would be appropriate for this dog?

Answer 3

A combination of the tranquilizer, acepromazine, and a mu agonist opioid such as hydromorphone.
A combination of the tranquilizer, acepromazine, and the kappa agonist/mu antagonist opioid, butorphanol.
A combination of an alpha-2 adrenergic agonist such as medetomidine, and the kappa agonist/mu antagonist opioid, butorphanol.

Question 4

You need to anesthetize a very active and nervous 6-month old Italian greyhound for an elective castration. Physical examination and lab data reveal a healthy dog.
What would be the least ideal induction choice for this dog?

Answer 4

Mask induction using isoflurane

Question 5

What drugs inhibit norepinephrine output in the brain producing sedation and analgesia?

Answer 5

An alpha-2 adrenergic agonist such as xylazine, detomidine, or romifidine

Question 6

What drugs act in the brain by enhancing activity of the inhibitory neurotransmitter GABA?

Answer 6

A benzodiazepine tranquilizer such as midazolam

A neurosteroid anesthetic agent such as alfaxalone

Question 7

What DEA controlled substances bind to specific receptors in the brain and spinal cord to prevent transmission of nociceptive information?

Answer 7

A mu agonist opioid such as morphine and hydromorphone

Question 8

What drugs act by inhibiting the excitatory neurotransmitter NMDA?

Answer 8

A cyclohexamine anesthetic agent such as ketamine or tiletamine

Question 9

True or False. Because sevoflurane is less potent than isoflurane, sevoflurane is considered to be a safer inhalant agent than is isoflurane.

Answer 9

False
Even though Sevo is newer than Iso, it is not safer. Sevo has a biometabolism at 4% and the chief metabolite is fluoride, which can lead to high renal failure in humans. Dogs are a bit more resistant, but Iso metabolism is less at 0.1% and therefore safer

Question 10

True or False. The inhalational anesthetic agents are unlikely to produce significant effects on cardiovascular function at clinically useful dosages

Answer 10

False

Question 11

True or False. The inhalational anesthetic agents are more potent in dogs than in horses

Answer 11

False

Question 12

True or false. Isoflurane and sevoflurane are primarily eliminated by hepatic metabolism.

Answer 12

False
Inhalant anesthetic agents are eliminated primarily from the body by diffusing down a partial pressure gradient from the body across the lungs, into the breathing system, and to the atmosphere

Question 13

True or false. Most inhaled anesthetic drugs produce minimal effects on respiratory function

Answer 13

False

It causes a dose-dependent depression; apnea at high doses

Question 14

True or false. Isoflurane and sevoflurane readily evaporate at room temperatures

Answer 14

True

Question 15

True or false. Sevoflurane is slightly less soluble in blood than is isoflurane; therefore, onset and recovery times are slightly faster with sevoflurane than isoflurane.

Answer 15

True

The less soluble the agent, the more rapid its uptake, the faster its action will be

Question 16

True or false. Vaporizers are required for concentration and delivery of isoflurane and sevoflurane because otherwise, inadequate amounts of the drugs would be delivered to the patient.

Answer 16

False

The problem is not inadequate drugs delivered, the problem is too much would be delivered in an uncontrolled state

Question 17

True or false. Sevoflurane is more potent than is isoflurane.

Answer 17

False

Sevoflurane has a MAC of 2.4 to 2.6 and isoflurane has a MAC of 1.3-1.6

Question 18

True or false. Nitrous oxide (N2O) is more potent than either isoflurane or sevoflurane.

Answer 18

False

N2O has a MAC of about 200%

Question 19

True or false. Desflurane is less likely to evaporate at room temperature than isoflurane.

Answer 19

False

Isoflurane is less likely to evaporate at 31% and desflurane will evaporate at 88%

Question 20

You have just calculated and administered a dose of the tranquilizer, acepromazine, for preanesthetic medication for a healthy Labrador retriever. About 20 minutes later, you notice the dog is recumbent and is tachycardic with weak pulses. You then realize you miscalculated and gave 10 times the appropriate dosage of acepromazine. What should you do now?

Answer 20

Place an IV catheter and give IV fluids

Question 21

What is the MAC of isoflurane in the unpremedicated dog?

Answer 21

1.3%

Question 22

What is the MAC of sevoflurane in the unpremedicated horse?

Answer 22

2.4%

Question 23

True or false. A benzodiazepine such as midazolam or diazepam given as the sole tranquilizing agent is a good choice for sedation of a 6-month old healthy kitten before an OHE.

Answer 23

False

Benzodiazepines should only be used alone to provide mild restrain in extremely debilitated or neonatal patients

Question 24

You need to sedate a pet, male castrated, Nubian goat to place a urinary catheter. The goat is sick as a result of a urethral obstruction (fairly common problem in male goats). He has a greatly enlarged urinary bladder. You need to provide sedation and analgesia, but you do NOT want to risk additional bladder enlargement; you need to avoid drugs that may cause diuresis. Which of the following classes of drugs would you therefore AVOID?

Answer 24

Alpha-2 adrenergic agonists

Question 25

You have just premedicated your surgical patient with the phenothiazine tranquilizer, acepromazine. Thirty minutes later, you notice the animal has become recumbent, has rapid, weak pulses and a high heart rate, prolonged capillary refill time, and cannot stand. Upon reviewing your drug calculation, you realize you have accidentally given 10 times the recommended dose of acepromazine. Based on what you know regarding the mechanism of action of acepromazine, what is your next step?

Answer 25

Give IV fluids

Question 26

Which of the following drugs would be a POOR choice to give to a well-controlled diabetic patient?

Answer 26

Alpha-2 adrenergic agonist

Question 27

You need to sedate an aggressive 3-year old Quarter horse stallion. Which of the following combinations will provide the most reliable sedation and analgesia without producing ataxia or recumbency?

Answer 27

The alpha-2 adrenergic agonist xylazine, plus the opioid butorphanol.

Question 28

Which of the following characteristics best describes the actions of alpha-2 adrenergic agonists (xylazine, medetomidine, romifidine, etc.)?

Answer 28

The drugs act centrally to produce sedation, analgesia, and muscle relaxation

Question 29

Speed of onset and recovery of inhalational anesthetic drugs is inversely proportional to which of the following properties?

Answer 29

Solubility

Question 30

If the MAC is higher, is the drug more or less soluble?

Answer 30

Less

Question 31

Which is more effective, a drug with an higher MAC or one with a lower MAC?

Answer 31

Lower

Question 32

Which will produce anesthesia faster, a drug with a high MAC or a low MAC?

Answer 32

Low

Question 33

What is the MAC inversely proportional to?

Answer 33

Potency

Question 34

True or false. Mu agonist opioids (such as morphine, hydromorphone, fentanyl) should not be used in animals with significant cardiovascular compromise

Answer 34

False

Opioids provide excellent analgesia with minimal cardiovascular compromise other than vagally-mediated bradycardia

Question 35

What animal is the least sensitive to the effects of alpha-2 adrenergic agonists (xylazine, medetomidine, detomidine, romifidine)?

Answer 35

Thoroughbred horse

Question 36

What are the expected effects of the alpha-2 adrenergic agonist dexmedetomidine?

Answer 36

Insulin inhibition
Diuresis
Sedation
Analgesia
Vasoconstriction

Question 37

What are effects of the anticholinergic drugs atropine and glycopyrrolate?

Answer 37

They decrease secretions and cause reduced intestinal motility

Question 38

Your patient was given acepromazine and hydromorphone as premeds, induced with propofol, and is being maintained on isoflurane. Which drug is MOST associated with intraoperative hypotension?

Answer 38

Acepromazine

Question 39

True or False: Vasodilation with sevoflurane is less than with isoflurane for a given MAC value.

Answer 39

False

Question 40

True or False: Loss of consciousness with inhalants is faster than with modern injectable agents.

Answer 40

True