Test 1 Flashcards
Afferent vs Efferent
Afferent to the CNS
Efferent from the CNS
What are the properties that are necessary to make a local anesthetic clinically useful?
- Compatible with the tissues and non irritating.
- Actions should be temporary and completely reversible.
- Effective in doses far below its toxic level.
- Hypoallergenic.
- Rapid onset of anesthesia with a duration of action sufficient to complete the dental procedure comfortable.
Two functional groups of local.
Amides and esters.
Are topicals typically esters or amides?
Esters.
What are some of the esters?
Procain, novocaine, etc.
What are some of the amide locals?
Lidocaine (xylocaine), mepivacaine (carbocaine), prilocaine (citanest), Bupivacaine (marcaine), etidocaine (duranest)
Lidocaine
xylocaine
Mepivacaine
Carbocaine
Prilocaine
Citanest
Bupivacaine
Marcaine
Etidocaine
Duranest
Why are amides preferable to the esters?
The means by which the body breaks down the substance of the drug is less likely to cause an allergic reaction. Additionally, the lipid solubility, potency, duration of action and ionization constant are all perferable.
Where are esters and amides broken down?
Esters are reduced by esterases in the tissue and amides are reduced in the liver and excreted in the kidneys.
How does the local anesthetic interfere with how the nerve impulses travel down the length of the nerve itself?
Interferes with the influx of Na ions across the neural membrane. Acts during the depolarization phase of the nerve impulse generation. The rate is reduced and the nerve never reaches the firing potential.
Where does local affect the nerves?
The axonal membranes of peripheral nerves.
The Specific Receptor Theory
The local anesthetic interferes with the sodium channel and blocks the sodium transfer necessary for nerve conduction.
How far must the anesthetic permeate in order to profoundly block?
8 to 10 mm of the nerve’s length.
What is a reason for anesthetic not producing pain control on the second injection?
The lower pH of the tissues, edema, hemorrhage or transudation in the surrounding area. Once the nerve has returned to function, it usually is more difficult to achieve profound anesthesia again.
Why isn’t anesthetic not as effective when infection is present?
Because the pH of the tissues is too low to allow the anesthetic to penetrate the nerve sufficiently.
What is the largest fiber? The smallest?
A is the largest. C is the smallest?
Type C Fibers
No myelin sheath. Responsible for carrying the sensations of pain and temperature. Smallest.
Which fiber is most easily blocked by local anesthetic? Why?
Type C! The lack of a myelin sheath allows easier access to the nerve.
Type A Fibers.
Largest, responsible for carrying pressure and motor sensation. Local is not as effective.
Why can an adequately anesthetized patient always feel pressure during an extraction, but not pain?
Type A fibers, which are the largest, and carry pressure and motor sensation, are not effectively blocked by local.
What influences the uptake of local anesthetics?
- Blood flow in the area of administration.
- Affinity of the anesthetic for local tissues
- Effect of the anesthetic on circulation.
- The absence or presence of a vasoconstrictor.
What types of organs will have higher blood levels of anesthetic following injection?
Highly vascular organs. Brain, liver, lungs, and kidneys.
Following an intravascular injection, what is the sequential distribution?
First to the lungs, then other organs with large blood supplies. Especially the brain, heart, liver kidneys, spleen. Finally to muscles and fat.
What happens at toxic levels of local anesthetics to the CNS and CVS?
CNS and CVS susceptible. Depresses the CNS and causes the patient to have convulsions. Epileptic patients are more susceptible to seizure.
CVS is more resistant. Myocardial depression followed by circulatory collapse is not caused by a typical dental dose.
What metabolizes ester anesthetics? Why is this a problem in some people?
Pseudocholinesterase.
Approximately 1 in 2800 people have atypical pseudocholinesterase and can’t biotransform the anesthetic at a normal rate.
Where are amides metabolized? Why does this cause an issue in some patients?
Liver! Patients who have liver dysfunction may have difficulty metabolizing and will reach a toxic level more quickly than a healthy counterpart.
When the liver isn’t fully functioning, how does the body compensate in the metabolism of amides?
The kidneys then excrete the amount that wasn’t metabolized in the liver.
Why is the vasodilation activity of local anesthetics bad?
Produces an increased rate of absorption. Decreased effectiveness, short duration of anesthesia and higher risk of toxicity. Bleeding in the area of injection is increased.
How do you counteract the vasodilation?
Vasoconstrictors. Decrease the absorption of the drug and prolong the anesthetic effect. Decreases the risk of toxicity because it is more slowly absorbed.
What needs to be considered when selecting an appropriate vasoconstrictor?
Length of the procedure, desired level of hemostasis and medical health of patient.
What are the most commonly used vasoconstrictors?
Epinephrine and levonordefrin (neo-cobefrin).
What are the handling instructions for epinephrine?
Sensitive to heat and can be inactivated if left too warm for too long. Store local in cool areas and never autoclave the cartridges.
Which is more potent, neocobefrin or epinephrin?
Epinephrine. 5 times the amount of neo-cobefrin is needed to produce the same results as epinephrine.
What concentrations of epinephrine available at? Why?
1:50,000 for better hemostasis. The anesthetic effect lasts much longer.
What is the rebound effect?
Vasoconstrictors are effective in producing hemostasis, but after they wear off, it may lead to increased postoperative bleeding. Especially true in higher concentrations.
What is the limit of cartridges of lidocaine for use on patients that are medically compromised by high bp, CV disease or hyperthyroidism?
No more than 2 cartridges of lidocaine with 1:100,000 concentration of epinephrine.
When is epinephrine is contraindicated in patients?
- bp over 200/115.
- Uncontrolled hyperthyroidism
- Severe cardiovascular disease, including less than 6 months after a myocardial infarction or cerebrovascular accident.
- Daily episodes of angina pectoris or unstable angina.
- Cardiac dysrhytmias despite appropriate therapy.
- Medicated with B blocker, MOIs, tricyclic antidepressents, general anesthesia with a halogenated anesthetic like halothane, methoxyflurane or therane.
Which reaches toxic levels easier, topical or local? Why?
Topical! The concentrations are higher and absorption is greater.
To what depth is topical anesthesia effective?
Only about 2-3 mm of depth into the tissues on which it is applied.
Why is the gel type of topical more recommended over spray?
It can be dispensed in pre-measured doses. Patient may aspirate the spray and the can is difficult to sterilize.
What is the commonly used topical anesthetic?
Benzocaine.
What is the maximum recommended dose of topical lidocaine?
200 mg.
What type of local anesthetic is benzocaine? An ester or an amide?
Ester. Localized allergic reactions may be noted.
What are some factors that influence the action of the local anesthetic?
Anatomical variation, type and method of injection, presence or absence of infection, the patient’s individual response to the anesthetic, anxiety, vascularity of tissues.
What is the duration of bupivacaine hydrochloride, 0.5% with epinephrine 1:200,000
Greater than 90 min.
What is the duration of Etidocaine hydrochloride, 1.5% with epinephrine 1:200,000?
Greater than 90 min.
What is the duration of lidocaine hydrochloride, 2% without vasoconstrictor?
30 min.
What is the duration of lidocaine hydrochloride, 2% with epinephrine 1:50,000?
60 min.
What is the duration of lidocaine hydrochloride, 2% with epinephrine 1:100,000?
60 min.
What is the duration of mepivacaine hydrochloride, 3% without vasoconstrictor?
30 to 60 min.
What is the duration of mepivacaine hydrochloride 2% with levonordefrin 1:20,000?
60 min.
What is the duration of prilocaine hydrochloride 4% without vasoconstrictor?
30 min.
What is the duration of prilocaine hydrochloride, 4% with epinephrine 1:200,000?
90 min
What is the duration of articaine, 4% with epi 1:100,000?
60 min.
What are the symptoms of epinephrine overdose?
Fear, anxiety, restlessness, headache, tenseness, perspiration, dizziness, tremor of limbs, palpitation, and weakness.
BP and heart rate will be elevated.
What do you do in the case of an epinephrine overdoes?
Position patient comfortably and administer oxygen. If the patient’s BP is elevated and signs of cerebrovascular incident occur, summon medical assistance. If no symptoms of cerebrovascular problems, the patient can be dismissed home.
How can toxicity be reached for an anesthetic?
Administering too much of the drug (body weight), administering the drug to a sensitive individual, administering the drug into a blood vessel, or by improper drug combinations.