Why are vasoconstrictors used?
A. Vasoconstrictors, like epinephrine and levonordefrin, are an important component of local anesthetic (LA) solutions for a number of reasons. By decreasing regional blood flow, they allow more LA to diffuse into the nerve as well as help maintain a higher LA concentration within and around the nerve, leading to a prolonged duration of pulpal and soft tissue anesthesia and a greater depth of anesthesia. Anesthesia ceases as the LA diffuses back out of the nerve and into the blood stream. The LA is yet not metabolized at this point (metabolism occurs in the liver). Once enough of the LA has diffused out of the nerve—the process is called redistribution—the drug is redistributed from an area of high concentration, eg, the nerve, into other parts of the body where there is a lesser concentration.
While the LA is in the nerve blocking nerve conduction, blood circulating through the area gradually absorbs the LA into the cardiovascular system, taking it away from the nerve and decreasing its concentration within the nerve. When enough LA has been taken away, nerve impulses begin to reach the patient’s brain and pain is experienced. The addition of a vasoconstrictor to the LA solution provides a longer duration and a deeper, more profound anesthetic. This is a major advantage of using epinephrine-containing LA solutions. Another significant advantage is that by retarding the absorption of the LA, the amount of drug found in the patients’ blood stream is decreased, increasing the safety margin of the LA solution.
With the amide LAs, allergy is not as significant a concern as is overdose (toxic reaction). An overdose of any chemical occurs when the level of that substance in the patient’s blood gets too high. By decreasing the rate of absorption of the LA into the blood stream, epinephrine helps keep the blood level of the anesthetic drug lower, which in turn, lowers the risk of an overdose.
Q. When using a local anesthetic without a vasoconstrictor should practitioners be more careful about the possibility of overdose?
A. Yes, however with adult patients, overdose secondary to over administration (as opposed to direct intravascular injection) is extremely rare. Extra care must be taken with smaller, lighter weight children (from less than 30 lbs to about 60 or 70 lbs).
Q. Are there any possible reactions to the use of vasoconstrictors?
AVasoconstrictors not indicated in certain instances. They are not necessary during a very short, superficial procedure that doesn’t require very long or very deep anesthesia. A patient does not need to be numb for 5 hours after a 15-minute procedure that could have been accomplished with a plain LA. Vasoconstrictors should also not be used on patients who respond adversely to them. Some people who receive a normal dose of a drug will overreact to it. An example is a patient who receives a local anesthetic injection with epinephrine 1:100,000 and then 5 to 10 minutes later, tells the dentist or hygienist that something is wrong. The patient may look fine but he or she reports shaky arms and legs. This patient is a hyperresponder to epinephrine. About 15% of any population overreacts to the average dose of a drug. Within that 15%, there will be some people who are even more hyperresponsive.1
The heart of hyperreactive patients beats faster in response to the normal clinical actions of epinephrine. Their skin turns red and they begin to sweat. This is commonly termed an epinephrine reaction. To avoid it, less epinephrine should be used. For example, if you administered 1:50,000 and a reaction occurred, 1:100,000 should be used next time. If the reaction happened with 1:100,000, then switch to 1:200,000 or try levonordefrin. Levonordefrin is epinephrine-like but it is not the same drug. It’s conceivable that a patient who has overreacted to epinephrine might not have the same reaction to levonordefrin.
Q What type of medical problems preclude the use of epinephrine?
AThere is no one medical problem that always contraindicates the use of epinephrine. It is the degree of severity of the patient’s problem that dictates this. For example, patients with angina experience chest pain when their heart begins to beat more rapidly. When this happens, their heart muscle requires more oxygen but because of the presence of coronary artery disease, the blood supply to the heart is compromised. There is a deficiency in oxygen supply to the myocardium, which results in chest pain (angina). A patient with angina is normally categorized by the American Society of Anesthesiologists (ASA) physical status classification system as an ASA 3 (ASA 1 is a normal, healthy patient; ASA 2 is a person who has a very mild medical problem; ASA 3 has a more severe medical problem that limits activity but is not incapacitating; and ASA 4 has a medical problem that is a constant threat to his or her life). The ASA 4 patient is not a candidate for elective dental treatment.
Q. Is epinephrine contraindicated for a patient with high blood pressure?
A. It depends on how high the blood pressure is. The University of Southern California School of Dentistry has had guidelines since 1973 for managing patients with varying degrees of elevated blood pressure. The cutoff for dental treatment is a systolic blood pressure of 200 or above and/or a diastolic of 115 or above. If a patient comes in with a blood pressure below 200, he or she is an ASA 1, 2, or 3 and is an acceptable candidate for elective dental care. A patient with blood pressure above 200 or 115, is an ASA 4 who has a medical condition that is life threatening. Any further elevation in blood pressure is more likely to precipitate an acute situation, such as a stroke or a myocardial infarction (MI).
Several factors are important when determining if a vasoconstrictor may be a potential problem for a patient who has suffered an MI in the past. If the MI happened within the past 6 months, the patient is an ASA 4 and elective dental care is contraindicated. If the MI took place more than 6 months ago, the ASA category will depend on the degree of residual damage to the heart. If minimal damage occurred (information that is gathered through discussion with the patient and/or consultation with his or her physician) and is functioning relatively normally, then an ASA 2 classification is appropriate. If more damage was done to the myocardium and the patient exhibits some signs of significant damage, such as shortness of breath, undue fatigue, or is suffering from anginal-type chest pain, an ASA 3 category is appropriate.
Q. Should the amount of vasoconstrictor used be limited with these types of patients?
A. If a patient is an ASA 3 because of cardiovascular problems, epinephrine is indicated for the purpose of better pain control. However, the amount of epinephrine administered should be limited. For example, rather than using 1:50,000 concentration, a 1:100,000 or 1:200,000 is preferred.
PREGNANT AND LACTATING PATIENTS
Q. Are there contraindications to using vasoconstrictors on patients who are pregnant?
A. All drugs approved for use by the Food and Drug Administration receive a pregnancy classification. The classifications are: A, B, C, D, and X. An A drug has demonstrated through clinical research to be safe during pregnancy. An X drug is absolutely contraindicated because there is positive evidence that the drug causes fetal damage. There are very few drugs categorized as A because it is extremely difficult to do clinical research on pregnant patients. All local anesthetics currently being used in dentistry are either B or C. Articaine, bupivacaine, lidocaine, mepivacaine, prilocaine, and epinephrine are Bs and Cs and are indicated for use in pregnant patients. Pregnancy is not a contraindication to the administration of either local anesthetics or vasoconstrictors.
They are also safe medications for use during lactation. Some patients may ask if the drug will be found in breast milk and the answer is yes. This may prevent some of these patients from wanting to receive local anesthesia. Even though it is safe for the child, if the patient doesn’t want it, local anesthetics either with or without epinephrine should not be administered.
Q. Should local anesthetics be avoided in the first trimester if possible?
A. We try to avoid doing anything that might potentially overly stress the patient during the period of fetal organogenesis (the first trimester of pregnancy). LAs do not induce spontaneous abortion nor do they produce fetal malformations. However, the first trimester of pregnancy is the time when most problems arise, so it makes little sense to administer a local anesthetic during this most fragile time of pregnancy. Unless it is a dental emergency, eg, pain and/or infection, avoid dental care during the first trimester. During the second and early third trimesters, it is less of a problem. During the later stages of the third trimester, there is still no problem except that the patient will likely be uncomfortable lying in the dental chair for any period of time due to the enlarged uterus pressing down on the abdomen.
Q. For lactating patients concerned about local anesthetics remaining in their breast milk, how quickly do local anesthetics leave the blood stream?
A. The distribution half-life of local anesthetics is the amount of time needed for the blood level to decrease by 50%. For example, if the half-life of a drug is 10 minutes, then in 10 minutes the blood level will have decreased by 50%. In two half-lives or 20 minutes, it’s decreased by 75%. In three half-lives or 30 minutes, it’s down by 87.5%. After six half-lives, which is a 98.5% decrease in blood level, the drug has been removed from the blood. The actual half-life of amide local anesthetics is 90 minutes, meaning six half-lives are 540 minutes or 9 hours. So 9 hours after receiving an amide anesthetic, the patient should be able to breast-feed with little to no LA being passed in the milk. Articaine, unlike other amide LAs, has a half-life of 27 minutes or 162 minutes—2 hours, 42 minutes—for six half-lives. Because the blood level of articaine decreases so quickly, it may be the preferred drug in this situation.
Stay tuned for more from Stanley F. Malamed, DDS, in upcoming issues of Dimensions of Dental Hygiene.
- Malamed SF. Handbook of Local Anesthesia. 5th ed. St Louis: CV Mosby; 2005.
From Dimensions of Dental Hygiene. September 2005;3(9):22, 24-25.