Ch. 6

Question 1

How do vasoconstrictors enhance the effects of local anesthetic drugs?

Answer 1

Vasoconstrictors constrict local vessels, increasing safety by slowing systemic absorption. This constriction also prolongs the local actions of the drugs, provides hemostasis, and increases the profoundness of anesthesia.

Question 2

When are vasoconstrictors useful in dental settings?

Answer 2

Vasoconstrictors are useful in dental settings where long durations and more profound anesthesia are routinely required.

Question 3

Name two vasopressors that are routinely included in dental local anesthetic drugs in North America.

Answer 3

There are two vasoconstrictors, also known as vasopressors, which are routinely included in dental local anesthetic drugs in North America — epinephrine and levonordefrin.

Question 4

Define epinephrine.

Answer 4

Epinephrine is a naturally occurring catecholamine. It is both a hormone and a neurotransmitter. It is a direct-acting sympathomimetic drug, and is used in some local anesthetic solutions.

Question 5

Define levonordefrin.

Answer 5

Levonordefrin is a synthetic catecholamine. It is a direct-acting sympathomimetic drug, and is used in some local anesthetic solutions.

Question 6

Are vasoconstrictors used in dentistry direct-acting, indirect-acting, or mixed-acting sympathomimetics?

Answer 6

Vasoconstrictors used in dentistry are direct-acting sympathomimetics.

Question 7

Using Table 6-1, provide the names of common sympathomimetic amines.

Answer 7

Table 6-1 Common Sympathomimetic Amines
Catecholamines:
Epinephrine*
Amphetamine
Norepinephrine*
Levonordefrin
Dopamine*

Noncatecholamines **:
Methamphetamine
Ephedrine
Phenylephrine
Amphetamine

• Naturally occurring chemicals
• • All are examples of chemicals found in street drugs, diet pills, and cold medications

Question 8

Explain why the lack of profound anesthesia can result in a spike in blood pressure.

Answer 8

The lack of profound anesthesia can result in unmanageable pain, which in turn can lead to a spike in blood pressure due to the release of endogenous epinephrine in response to the pain. This endogenous release may be much greater than doses of exogenous epinephrine typically administered.

Question 9

What are the possible local and systemic effects of adrenergic vasoconstrictors?

Answer 9

Adrenergic vasoconstrictors used in dental procedures typically do not produce noticeable effects but are capable of causing undesired local and systemic reactions. Local effects may include ischemia and necrosis while systemic effects may include changes in arterial blood pressure, palpitations, dysrhythmias, and even permanent injury or death due to ventricular fibrillation, heart attack, or stroke. Overdose, intravascular administration, drug interactions, and intolerance increase the likelihood of adverse events.

Question 10

Why are most adverse events related to the use of vasoconstrictors short-lived?

Answer 10

Most adverse events related to the use of vasoconstrictors are short-lived due to their efficient reuptake in synapses, and the rapid removal and biotransformation of any residual portions that enter the bloodstream.

Question 11

Name the types and subcategories of adrenergic receptors.

Answer 11

Two types of adrenergic receptors were identified by Ahlquist in 1948, alpha (α) and beta (β). Since that time, subcategories have been identified which explain specific actions of vasoconstrictors.

Question 12

Which receptors are responsible for smooth muscle contraction in peripheral arterioles and veins?

Answer 12

Alpha (α) receptors are responsible for smooth muscle contraction in peripheral arterioles and veins throughout the body (peripheral vasoconstriction).

Question 13

Which receptors are responsible for smooth muscle relaxation such as bronchodilation and vasodilation?

Answer 13

Beta 2 (β2) receptors are responsible for smooth muscle relaxation such as bronchodilation and vasodilation.

Question 14

What concentrations of epinephrine are available in local anesthetic solutions in North America?

Answer 14

Epinephrine is added to local anesthetic solutions in North America in concentrations of 1:50,000, 1:100,000, and 1:200,000.

Question 15

A patient calls the office approximately six hours after a tooth extraction to report an increase in bleeding. What is a likely cause of increased bleeding?

Answer 15

Epinephrine provides nearly equal α and β effects, but not at the same time. Initial α vasoconstriction of peripheral vasculature allows time for the anesthetic drugs to bind to receptor sites. Later, β2 vasodilation predominates. This has been observed before and after surgery where epinephrine has been administered. Initially, α effects enhance profound, durable anesthesia and reduce hemorrhaging at surgical sites. Postoperatively, the dominant β2 effects can result in increased bleeding approximately 6 hours after surgery.

Question 16

What is the maximum dose of epinephrine for use in dentistry in a healthy individual?

Answer 16

The maximum dose of epinephrine for use in dentistry in healthy individuals has been determined to be 0.2 mg per appointment.

Question 17

Give examples of situations in which the dose of epinephrine should be reduced.

Answer 17

In individuals with significant cardiovascular compromise (ASA categories III & IV), and other medical situations, including elderly populations and in the presence of a number of specific drug interactions, the dose of epinephrine should be reduced.

Question 18

What is the maximum appointment dose of epinephrine for individuals at risk?

Answer 18

The standard maximum dose of epinephrine is 0.2 mg per appointment. For individuals at risk, the dose is reduced to one-fifth, or 0.04 mg maximum dose of epinephrine per appointment.

Question 19

Why does the use of vasoconstrictors increase the risk of subsequent cerebrovascular accident (CVA) or stroke in individuals with a history of previous CVA?

Answer 19

A history of a cerebrovascular accident (CVA) or stroke increases the risk of experiencing a subsequent CVA due to increases in blood pressure in response to vasoconstrictors.

Question 20

Compare the action of levonordefrin to epinephrine on adrenergic receptors.

Answer 20

Levonordefrin’s action is primarily α, 75% versus 25% β. Epinephrine is 50% α and 50% β effects. As a weak stimulator of beta adrenergic receptors, levonordefrin is similar to norepinephrine which is approximately 90% α. Despite levonordefrin’s major effect on α receptors, epinephrine is a more powerful vasoconstrictor of peripheral vasculature, thus providing much better hemostasis compared to levonordefrin.

Question 21

Compare the potency of levonordefrin to epinephrine.

Answer 21

Levonordefrin is less potent compared to epinephrine and is formulated in dilutions of 1:20,000, which is five times more concentrated (less diluted) than a 1:100,000 epinephrine solution.

Question 22

What are the signs and symptoms of high levels of plasma epinephrine?

Answer 22

The signs and symptoms of high levels of plasma epinephrine include nausea, restlessness, a racing heart, severe headaches, palpitations, tremors, and shakiness. Note that many of these signs and symptoms mimic those observed in anxiety and fear.

Question 23

How is epinephrine removed from the system?

Answer 23

Epinephrine is uptaken in the synaptic nerve junctions and recycled. The epinephrine that is not recycled is biotransformed by the enzyme catechol-O-methyltransferase (COMT), and further breakdown may occur via monoamine oxidase (MAO).

Question 24

Explain the terms hyper-response versus hypersensitivity.

Answer 24

The term hyper-response refers to overdose manifestations to less than maximum recommended doses in some individuals. This is the normal response for these individuals and although the doses are below maximum recommended levels, they are dose related. Hyper-response can occur in individuals who experience a rapid, direct, and vigorous stimulation of adrenergic receptors by a vasoconstrictor.
Hypersensitivity refers to an allergic process which involves humoral, cell- mediated, and/or antigen-antibody reactions. These responses are not dose related. A true epinephrine allergy is not possible because epinephrine in local anesthetics is identical to endogenous epinephrine.

Question 25

Give examples of clinical signs and symptoms of an allergic response.

Answer 25

Hives, rash, bronchospasm, and vasodilation are examples of clinical signs and symptoms that occur with an allergic response.

Question 26

Give examples of other vasoconstrictors that are used in regions other than North America.

Answer 26

Norepinephrine, phenylephrine, and felypressin are not currently available in dental local anesthetic preparations in North America; however, all three vasoconstrictors have been in use in other regions of the world for many years.

Question 27

In the Elena Gagarin case study, the clinician elected to use a local anesthetic without, or with limited, vasoconstrictor. What was the reason for this precaution?

Answer 27

A severe spike in blood pressure and reflexive bradycardia are more likely to occur in the presence of tricyclic antidepressants in some individuals if vasoconstrictors are used. Epinephrine may be administered, but the total quantities of drug should be limited.