hazards of local anesthesia

Local Anesthesia problems and hints

Iyad M.Abou RabiiDDS. OMS. MSc. PhD

Contents

Failure of Local Anesthesia

L A Local Hazards

LA General Hazards

LA General Hazards

LA Toxic effects

Adverse effects are usually caused by high plasma concentrations of a local anesthetic drug that result from

– inadvertent intravascular injection,

– excessive dose or rate of injection,

– delayed drug clearance,

– or administration into vascular tissue.

LA Toxic effects

Possible adverse effects include the following:

CNS: High plasma concentration initially produces CNS stimulation (including seizures),

followed by CNS depression (including respiratory arrest). The CNS stimulatory effect may be absent in some patients, particularly when amides are administered.

Solutions that contain epinephrine may add to the CNS stimulatory effect.

Cardiovascular: High plasma levels typically depress the heart and may result in bradycardia, arrhythmias, hypotension, cardiovascular collapse, and cardiac arrest.

Local Anesthesia Allergic shock

Esters are highly allergenic, their use should be avoided and restricted to special cases after allergy test.

There has never been a true, documented allergic reaction to an amine anesthetic.

a patient may in fact be allergic only to the bisulfite preservative used to stabilize the vasoconstrictor.

If the allergic reaction was not too serious, it may be worth trying again with either mepivicaine or prilocaine without vasoconstrictor. Anesthetic manufactures do not use preservatives in carpules that do not also contain vasoconstrictor.

Signs and symptoms of anesthetics allergic reaction

The signs and symptoms of allergic reaction include:

– generalized body rash or skin redness

– itching, urticaria (hives)

– broncospasm (difficulty breathing)

– swelling of the throat

– asthma

– abdominal cramping

– irregular heartbeat

– hypotension (low blood pressure)

– swelling of the face and lips (angioneurotic edema)

Anaphylactic shock

Fortunately, the majority of allergic reactions to local anesthetics are fairly mild

In a very serious anaphylactic reaction, the patient may experience serious difficulty breathing due to closing down of the bronchioles in the lungs or swelling in the throat area due to urticaria as well as seriously low blood pressure leading to anaphylactic shock. This set of events, left untreated can lead to death.

Testing for anesthetic allergy using skin test

T.R.U.E. Test®

This is a patch test that applies 23 allergens to the skin contained in 12 polyester patches. One of the patches contains a mixture of several anesthetics and is used to test for allergy to local anesthetics in general. The mixture used includes two ester based anesthetics and one amine based anesthetic. This mixture of anesthetics is called the "Caine Mix"

Management of anaphylactic shock : 1

Position the patient on his or her back with the feet elevated.

Maintain an airway

If the patient is not breathing on his own, use rescue breathing like you learned in CPR class.

Check the carotid artery for heartbeat and use chest compressions if necessary.


The two drugs that you must have on hand to stabilize a patient in anaphylactic shock are as follows:

– Epinephrine (adrenalin) 1:1000 subcutaneous injection. It opens the bronchioles allowing free breathing, increases the blood pressure counteracting shock and evens out and intensifies the heart beat. Its effects are drastic, but short lived. The standard dose is 1 mg given in three doses five minutes apart.

– Benedryl (diphenhydramine) 25-50 mgm injectable. This is an antihistamine and can also be taken in pill form an hour before the procedure to help prevent serious allergic reaction before it begins. Injectable diphenhydrimine which can be administered either subcutaneously, or in the buccal fold if the dentist is more comfortable with that route.


The following drugs are of little use to the dentist during the initial stages of the emergency since they are generally used by EMS personnel

– Aminophylline This drug opens blocked breathing passages.

– Solu-cortef IV injection. This drug is a corticosteroid and reduces the generalized allergic inflammatory reactions on a longer term basis. It will not act rapidly enough to reverse anaphylaxis immediately, but is more of a long term remedy.

– Wyamine injection. This drug is used to counteract hypotension (low blood pressure and shock) on a prolonged basis.

LA Local Hazards

Pain on injection

This is to a certain degree inevitable, but can be by patient relaxation; application of topical LA; stretching the mucosa; and slow, skilful, accurate injection of slightly warmed solution in reasonable quantities. Causes of pain include:

Touching the nerve when giving blocks, resulting in electric shockâ€™ sensation and followed by rapid analgesia (it is extremely rare for any permanent damage to occur).

Injection of contaminated solutions (particularly by copper ions from a pre-loaded cartridge). Avoid by loading the cartridge immediately prior to use.

Subperiosteal, and intraligamentary injections are painful and unnecessary, avoid.

Pain on injection (Prevention and Management)

This is to a certain degree inevitable, but can be by

– patient relaxation;

– application of topical LA;

– stretching the mucosa;

– and slow, skilful, accurate injection of slightly warmed solution in reasonable quantities.

Paresthesia

If the needle passes through a nerve in the area of injection, it may damage the nerve and cause paresthesia. The injury is usually not long term or permanent.

Make a note in the chart if the patient reports a shooting feeling during the injection that would indicate needle contact with the nerve.

A local anesthetic that has been contaminated by alcohol or a sterilizing solution may cause tissue irritation and edema, which will in turn constrict the nerve and lead to paresthesia.

Paresthesia (Prevention and Management)

Proper injection protocol and care of the dental cartridges will reduce the incidence of paresthesia, but it can still occur.

If the patient calls reporting paresthesia, explain to them that it is not an uncommon result of an injection and make an appointment for examination.

Make a note of the conversation in the patient's chart.

Paresthesia (Prevention and Management)

The condition may resolve itself within 2 months without treatment. Examine the patient and schedule them for reexamination every 2 months until sensation returns.

If the paresthesia continues after one year, refer the patient to a neurologist or oral surgeon for a consultation.

If further dental treatment is required in the area, use an alternate local anesthetic technique to avoid further trauma to the nerve.

Hematoma

The needle can nick vessels as it passes through highly vascular tissues. A nicked artery will usually result in a rapid hematoma, while a nicked vein may or may not result in a hematoma.

Hematomas most often occur during a posterior superior alveolar or inferior alveolar nerve blocks.

Use a short needle for the PSA and be conscious of depth of penetration for these injections.

Hematoma (Prevention and Management)

Use a short needle for the PSA and be conscious of depth of penetration for these injections.

If the hematoma develops during an inferior alveolar nerve block, apply pressure to the medial aspect of the mandibular ramus. The manifestations will usually be intraoral.

If the hematoma develops during an infraorbital nerve block, apply pressure to the skin directly over the infraorbital foramen. The discoloration will be below the lower eyelid.

If the hematoma develops during a mental or incisive nerve block apply pressure over the mental foramen. The skin will discolor over the mental foramen and swelling will occur in the mucobuccal fold.

If the hematoma occurs during a posterior superior

Hematoma (Prevention and Management)

If the hematoma occurs during a posterior superior alveolar nerve block, the blood will diffuse into the infratemporal fossa, and swelling will appear on the side of the face just after the injection is completed. The swelling occurs after a significant amount of blood has diffused, so direct pressure is often useless. Apply external ice.

The hematoma will disperse within 7 to 14 days with or without treatment. Avoid dental therapy in the area until the tissue is healed.

Trismus

Trismus is a motor disturbance of the trigeminal nerve and results in a spasm of the masticatory muscles causing difficulty in opening the mouth.

Trismus can be caused by

– trauma to muscles

– or blood vessels in the infratemporal fossa,

– injection of alcohol or sterilizing solution contaminated local anesthetic

– hemorrhage,

– large volumes of anesthetic solution deposited in one area,

– or infection.

Trismus (prevention)

Use of

– disposable needles,

– antiseptic cleansing of the injection site,

– aseptic technique,

– and atraumatic injection technique

will help prevent trismus.

Trismus (Management)

Recommended treatment for trismus includes heat therapy with moist hot towels 20 minutes every hour, analgesics, and muscle relaxants if necessary.

The patient should be instructed to exercise the area by opening, closing, and lateral excursions of the mandible for 5 minutes every 3 to 4 hours.

The patient can chew sugarless gum to facilitate lateral movement of the TMJ.

Trismus (Management)

Continue therapy until the patient has no symptoms. If the pain continues over 48 hours, an infection may be present.

Antibiotic therapy for 7 full days is indicated. If there is no improvement after 2 to 3 days without antibiotics or 7 to 10 days with antibiotics, refer the patient to an oral surgeon for evaluation.

Infection (Prevention)

Infection from a dental injection has become rare due to the use of sterile disposable needles and one-patient use cartridges.

The needle will always be contaminated when it comes in contact with the patient's mucosa.

Proper tissue preparation and sterile technique will virtually eliminate infection at the injection site.

Infection (Management)

The patient reports post injection pain and dysfunction one or more days following treatment,

manage as with trismus. If the symptoms do not resolve within three days, prescribe a seven day course of antibiotic therapy. (Usually 500 mg. penicillin V immediately then 250 mg. four times a day or erythromycin if the patient is allergic to penicillin.)

Record the incident and treatment in the patient's chart.

Broken Needles

The most common cause of needle breakage is sudden unexpected movement of the patient.

Smaller gauge needles (size 30) are more likely to break than larger ones (size 25).

Some practitioners habitually bend the needle and the metal is weakened in this area.

Broken Needles (Prevention)

The best way to avoid needle breakage is to routinely use a 25-gauge needle for any injection where there is a significant penetration of tissue.

The hub is the weakest part of a needle, so unless the injection technique specifically requires it, the needle should not be inserted all the way to the hub. A longer needle should be used.

Broken Needles (Management)

When a needle breaks, remain calm.

Instruct the patient to keep their mouth open, and if at all possible, place a biteblock. If an end of the needle is visible, retrieve it with a hemostat or cotton pliers.

If it is not visible, do not try to retrieve it at this time. Explain to the patient what has happened.

Make a note in the patient's chart about the incident.

Send the patient to an oral surgeon for consultation.

They may surgically remove the fragment or if the procedure will cause too much damage they may leave it where it is.

Other problems with LA administration

Lacerated artery May be followed by an area of ischaemia in the region supplied, or painful haematoma. Rare.

Lacerated vein Followed by a haematoma which resolves fairly quickly.

Facial palsy Can be caused by incorrect distal placement of the needle tip, allowing LA to permeate the parotid gland. The palsy lasts for the duration of the LA.

Failure of Local Anesthesia

Failure of Anesthesia

Pathological causes

Psychological causes

Anatomical causes

Operator dependent

Failure of anesthesia

Psychological causes of failure

Pathological causes of failure of anesthesia

– Factors precluding access

– Inflammation


Anatomical causes of failure of anesthesia

– Soft-tissue analgesia is more easily obtained, needing a lower degree of penetration of solution into nerve bundles, than does analgesia from pulpal stimulation.

– A numb lip does not indicate pulpal anaesthesia.

– Accessory nerve supply

– Barriers to anaesthetic diffusion

– Dense compact bone can prevent a properly given infiltration from working. Counter by using intraligamentary or regional LA.

Accessory nerve supplies


Operator dependent causes of failure of Anesthesia

– Choice of LA

– Poor technique

• inadequate volume of LA.

• Injection into a muscle (will result in trismus which resolves spontaneously).

• Injection into an infected area (which should not be done anyway as this risks spreading the infection).

• Intravascular injection; clearly of no analgesic benefit. Small amounts of intravascular LA cause few problems.

Management of failure of Anesthesia

A technique suggested for patients who have experienced local anesthetic failure in the mandible is

Failure Management : Mandible

Management of failure of Anesthesia

A technique suggested for patients who have experienced local anesthetic failure in the maxilla is

Failure management : Maxilla

Important general points

Thick nerve trunks require more time for penetration of solution and more volume of LA.

In nerve trunks autonomic functions are blocked first, then sensitivity to temperature, followed by pain, touch, pressure, and motor function.

Soft tissue anesthesia is reached before the levels needed for pulpal anesthesia, which takes several minutes and will wear off first (usually within an hour of a standard lidocaine/adrenaline LA).

Disinfection of mucosa prior to LA is not required in reality; however, sterile disposable needles are absolutely mandatory due to risks of cross-infection.

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