Local Anesthetic Use In Children
Children should have a comfortable experience when going to the dentist. Local
anesthetics are an important tool for the control of pain and discomfort during
dental treatment. Local anesthesia is safe when the appropriate technique is
used. Children remain conscious when a local anesthetic is given.
Local anesthetics are the most commonly used drugs in dentistry. Local
anesthetics work by interfering with nerve signals. Anesthetics prevent the
production and propagation of nerve signals. Local anesthetics are administered
300 million times annually in the United States.
The dose of local anesthetic should be lowered when children are sedated,
however. Dentists using drugs for pediatric sedation should have additional
training, and be prepared to manage the serious reactions that are possible.
Possible complications include convulsions and respiratory depression. Lidocaine
is the most commonly used local anesthetic.
WHAT TYPES OF LOCAL ANESTHETIC ARE THERE?
Dental local anesthetics fall into two groups: amides and esters. The
names are derived from the type of chemical link between the two ends
(aromatic and base) of the local anesthetic molecule.
The majority of local anesthetics used today, including lidocaine,
are tertiary amines.
All local anesthetics are amphipatic. That is, they have both lipophilic
and hydrophilic characteristics - usually at opposite ends of the anesthetic
molecule. The lipophilic end of the molecule is attracted to lipids, and the
hydrophilic end is attracted to water.
HOW DOES A LOCAL ANESTHETIC WORK?
Local anesthetics create a chemical roadblock between the source of the
pain or stimulation – and the brain.
The function of a nerve is to carry messages from one part of the body to
another. These messages are in the form of electrical signals called action
Local anesthetics block the operation of a specialized gate, called the
sodium channel. When the sodium
channel of a nerve is blocked, nerve signals cannot be transmitted.
The only site at which the local anesthetic molecules have access to the
nerve membrane is at the nodes of Ranvier, where there is an abundance of
sodium channels. The interruption of a nerve signal in a myelinated
nerve (dental nerve) occurs when nerve depolarization (the nerve signal)
is blocked at 3 consecutive nodes of Ranvier – a length of about 8 to 10
A vasocontrictor (which constricts blood vessels) is usually added to
local anesthetic solution to prolong the duration of anesthetic action. The
vasoconstrictor, such as epinephrine, works by slowing the removal of the
anesthetic from the vicinity of the nerve.
The potency of a local anesthetic is directly related to its lipid
solubility, since 90% of the nerve cell membrane is composed of lipid.
The more acidic the local anesthetic solution is, the slower the onset of
action, however. In addition, the more closely the equilibrium pH (the pKa)
for a given anesthetic approximates physiologic pH, the more rapid the onset
of anesthetic action.
Finally, the better the local anesthetic molecule binds to the protein in
the sodium channel of the nerve, the longer the anesthetic will be
WHY DON’T SOME CHILDREN GET NUMB?
An imperfect injection technique is the most common cause of problems with
Another common cause of problems is that local anesthetics do not work
well in an acidic environment - such as an inflamed or abscessed area. It is
therefore sometimes useful to control a dental infection with antibiotics
before a local anesthetic can be successfully used.
All other factors being equal, the single most important determinant of
local anesthetic potency is its lipid solubility, however.
HOW IS A LOCAL ANESTHETIC ADMINISTERED?
An important requirement for administering a local anesthetic is for the
dentist to be familiar with the manner in which the teeth are innervated.
Second, the dentist should use the smallest possible dose which achieves
adequate anesthesia. The maximum dose for lidocaine injection in children is
4.5 mg/kg per appointment. The dose of local anesthetic should be adjusted
downward when children are sedated, however.
When anesthetizing in the maxillary
arch, the dentist should recall that the permanent first molar’s
mesiobuccal root is innervated by fibers from the middle superior alveolar
nerve branch, while the remaining roots are innervated by the posterior
superior alveolar nerve branch. This means that at least two injections are
required for anesthetizing this tooth.
The primary maxillary second molar is innervated by both the posterior
superior alveolar nerve and the middle superior alveolar nerve branches.
Dentists should remember that the greater palatine nerve has accessory
nerve fibers that innervate the palatal roots of the upper primary and
In the mandibular
arch, the only guaranteed way to accomplish profound pulpal anesthesia
is to perform an inferior
alveolar nerve block. Primary incisors, however, can be anesthetized
using supraperiostial injections – which anesthetizes branches of the
ARE LOCAL ANESTHETICS SAFE FOR CHILDREN?
When administered correctly, local anesthetics are safe for children.
Since the 1960’s, dentists have begun using an aspirating
syringe, which has a small internal harpoon that engages the rubber
stopper of the local anesthetic carpule. This technique enables dentists to
aspirate for blood, and see if the needle has inadvertently entered a blood
vessel - before injecting the anesthetic solution.
Local anesthetics have a low margin of safety between the effective dose
and the toxic dose. The lethal dose for many local anesthetics is only 3
times that of the effective dose.
Deaths following local anesthetic administration are almost always a
result of overdosage. The maximum safe dose of lidocaine for a child is 4.5
mg/kg per dental appointment.
Bupivicaine (Marcaine) is an amide local anesthetic with a high toxic
potential, and should not be used in children. The duration of anesthesia
with bupivicaine can be as long as 24 hours.
Lidocaine is less toxic than many other local anesthetics, because its
interactions with the cardiac sodium channel are “fast in – fast out,”
whereas a local anesthetic such as bupivicaine is "fast in – slow
The cardiac dysrhythmias caused by bupivicaine overdose are difficult to
treat, because the plasma concentration which causes convulsions is close to
that which causes cardiovascular collapse. Thus, there is no advance warning
of an impending cardiovascular collapse.
When sedating a child, the local anesthetic dose should be lowered to
decrease the risk of toxicity and complications.
Finally, in a neonate, repeated doses of an amide local anesthetic such as
lidocaine, puts the newborn at greater risk for toxicity than an older
child. The reason for this problem is that the P-540 enzyme system, in the
liver, is poorly developed at birth.
MANAGEMENT OF LOCAL ANESTHETIC COMPLICATIONS:
Step One: prevent complications by being prepared. Know your patient. The
treating clinican must always obtain a current medical history of the
patient before initiating any treatment.. The dentist should be certified in
Basic Life Support, and be familiar with either Pediatric Advanced Life
Support or Advanced Cardiac Life Support. The doctor should have proper
resuscitation equipment on hand in case of an emergency.
Step Two: immediately stop the dental procedure, and activate the EMS
Step Three: evaluate and recognize the signs and symptoms of a local
anesthetic emergency. In a lidocaine overdose emergency, the patient will
initially complain of lightheadedness, tinnitus (ringing in the ears),
numbness around the mouth, a metallic taste, and double vision. With higher
toxic doses of lidocaine, tremors will develop and eventually coalesce into
a grand mal seizure. CNS (central nervous sytem) depression may lead to
respiratory arrest. It is essential to monitor blood pressure and vital
signs during an emergency so that an accurate diagnosis of the problem can
Step Four: secure and protect the patient’s airway.
Step Five: provide 100% oxygen via a nasal mask, or assist breathing with
a resuscitation bag – if necessary.
Step Six: ensure adequate blood circulation. Begin CPR if necessary.
Step Seven: if a seizure occurs, protect the patient from self-injury. It
is not necessary to put anything into the patient’s mouth – as long as
the airway remains open. Seizure activity may be controlled with 5-10 mg IV
Valium. Avoid giving Dilantin during a seizure because it may worsen the
toxic effects of a lidocaine overdose.
WHAT CAUSES LOCAL ANESTHETIC COMPLICATIONS?
Deaths following local anesthetic administration are almost always the
result of an overdose. The maximum safe dose of lidocaine for a child is 4.5
mg/kg per dental appointment. For example: a 35 lb child should never
receive more than 2 carpules of 2% lidocaine during a dental appointment.
Adverse reactions to local anesthetics occur primarily in the CNS and
cardiovascular system, because these tissues are also composed of excitable
If a local anesthetic (with epinephrine) is accidentally injected into a
blood vessel or a very vascular area, the patient is likely to experience
flushing of the skin, tachycardia (very fast heat rate), and nausea. The
hypertension (increased blood pressure) and tachycardia is due to the
epinephrine in the anesthetic. Constant blood pressure monitoring is
therefore essential for diagnosing the nature of the anesthetic emergency.
Most reactions reported by patients as “allergies” are actually caused
by an intravascular (blood vessel) injection with local anesthetic - or from
the uptake of epinephrine from the anesthetic solution.
No more than 1 percent of reactions to local anesthetics are true
allergies. The most common cause of a true allergic reaction to a local
anesthetic is sensitivity to the preservative in the anesthetic solution.
Methylparaben and bisulfites are widely-used preservatives, and may be the
offending agents in a true allergy to local anesthetic. For patient who are
sensitive to these preservative, the dentist should consider using a
mepivicaine preparation which contains no methylparaben.
When a topical local anesthetic (benzocaine) is used, the metabolite PABA
(para-aminobenzoic acid) may also be responsible for a true allergic
reaction in some people.
Allergic hypersensitivity reactions demonstrate a variety of symptoms,
ranging from a mild rash to anaphylactic shock.
Finally, both benzocaine and prilocaine produce metabolites which can
cause methemoglobinemia. These metabolites cause the oxidation of the ferric
form of hemoglobin to the ferrous form.
TIPS FOR CLINICIANS:
Apply topical anesthetic to the injection site(s) for one minute prior to
giving the injection.
Consider using a small mouth prop during the injection procedure. This
will help provide access and visibility, prevent injury, and will help
direct the needle to the correct injection site.
Don’t let the child see the needle.
Use the Explain-Practice-Do technique for giving local anesthetic to
children. Tell the child what he/she will feel during the procedure. Stress
the importance of holding still during the administration of local
Make sure that you or your assistant will be able to control any of the
child’s sudden head or hand movements during the injection.
Be gentle when administering local anesthetic to a child. Give the
injection very slowly to avoid discomfort.
Aspirate frequently to avoid injecting into a blood vessel. Use an
aspirating-type syringe which has a tiny harpoon that engages the rubber
stopper of the anesthetic carpule.
Use the smallest and shortest needle which will do the job.
Use the smallest dose of local anesthetic which will achieve adequate
anesthesia. The dentist should consider the child’s weight and medical
history in determining the correct dose of local anesthetic. Never give more
than 4.5 mg/kg of lidocaine per dental appointment.
Remember that the mandibular
foramen in a child is located slightly below the plane of occlusion. In
addition, the foramen is located more anterior than in adults – due to the
narrow anterioposterior width of a child’s mandible.
If an upper primary or permanent molar is not “getting numb,” try
giving a greater palatine nerve injection. In children, it is usually
adequate to infiltrate under pressure into the gingival sulcus of the
troublesome upper molar.
The long buccal nerve will sometimes innervate the lower primary or
permanent molars, especially when placing a rubber dam clamp. This nerve
passes lateral to the body of the mandible, and should be anesthetized
slightly buccal to the last tooth being treated.
The mylohyoid nerve sometimes gives accessory innervation to the lower
teeth. A submucosal deposition of anesthetic at the medial surface of the
mandible, at its junction with the floor of the mouth, will usually stop the
Remember to warn the child not to bite the “numb” cheek or lips. Give
the warning during the dental appointment as well at the end of the
A case report in the Journal of the American Dental Association
describes complications caused by a local anesthetic injection. A 33
year-old patient received an inferior alveolar nerve block at her
dentist’s office. Within one minute of the injection, the facial skin,
intraoral structures, and eye were adversely affected on the left side.
Presumably, the epinephrine in the local anesthetic was injected into the
inferior alveolar artery, traversed backward into the internal maxillary
artery, and affected the whole left side of the face. Within 45 minutes of
the injection, however, all unusual findings dissipated.