Complications of Local Anaesthesia

Anaesthetic toxicity (overdose)

While rare in adults, young children are more likely to experience toxic reactions because of their lower weight. Most adverse drug reactions occur within 5-10 minutes of injection. Overdose of local anaesthetics are caused by high blood levels of anaesthetic as a result of an inadvertent intravascular injection or repeated injections. Local anaesthetic overdose results in excitation followed by depression of the central nervous system and to a lesser extent of the cardiovascular system.

Early subjective symptoms of the central nervous system include dizziness, anxiety and confusion and may be followed by diplopia, tinnitus, drowsiness and circumoral numbness or tingling. Objective signs include muscle twitching, tremors, talkativeness, slowed speech and shivering followed by overt seizure activity. Unconsciousness and respiratory arrest may occur.

The initial cardiovascular system response to local anaesthetic toxicity is an increase in heart rate and blood pressure. As blood plasma levels of the anaesthetic increase, vasodilatation occurs followed by depression of the myocardium with subsequent fall in blood pressure. Bradycardia and cardiac arrest may follow.

Local anaesthetic toxicity is preventable by following proper injection technique, i.e., aspiration during slow injection. Clinicians should be knowledgeable of maximum dosages based on weight. If lidocaine topical anaesthetic is used it should factored into the total administered dose as it can infiltrate into the vascular system. After injection the patient should be observed for any possible toxic response as early recognition and intervention are the keys to a successful outcome.

Allergic reactions

Although allergic reactions to injectable amide local anaesthetics are rare, patients may exhibit a reaction to the bisulfite preservative added to anaesthetics containing epinephrine. Patients with a sulfa allergy should not receive articaine. Patients may also exhibit allergic reactions to benzocaine topical anaesthetics. Allergies can manifest in a variety of ways including urticaria, dermatitis, angioedema, fever, photosensitivity and anaphylaxis.


Paresthesia is the persistence of anaesthetic symptoms beyond the expected duration. It can be caused by trauma to the nerve by the needle during injection. It can also be caused by hemorrhage in and around the nerve. Reports of paresthesia are more common with articaine and prilocaine and thus nerve block should be avoided in children with these local anaesthetics. The tongue and lips are the most common areas affected. Most cases resolve in 8 weeks without treatment.

Postoperative soft tissue injury

Accidental biting or chewing of the lip, tongue or cheek is a problem seen in very young pediatric mentally or physically disabled patients. Soft tissue anaesthesia lasts longer than pulpal anaesthesia and may be present for up 4 hours after local anaesthesia administration. The most common area of trauma is the lower lip and to a lesser extent the tongue, followed by the upper lip.

Several preventive measures can be followed:

  • Select a local anaesthetic with a duration of action that is appropriate for the length of the planned procedure.
  • Advise the patient and accompanying adult about the possibility of injury if the patient bites, sucks or chews on the lips, tongue and cheek. They should delay eating and avoid hot drinks until the effects of the anaesthesia are totally dissipated.
  • Reinforce the warning with patient stickers and by placing a cotton roll or rolled up gauze (“Bite on the ghost”) in the mucobuccal fold if anaesthesia symptoms persist.
  • The management of soft tissue trauma involves reassuring the patient and parent (it’s okay if the tissue turns white), allowing up to a week for the injury to heal, and lubricating the area with petroleum jelly or antibiotic ointment to prevent drying, cracking and pain.11
preventive measures

In May 2008 the FDA approved OraVerse (Novalar Pharmaceuticals, Inc., San Diego, CA) (phentolamine mesylate) as the first pharmaceutical agent indicated for the reversal of soft tissue anaesthesia (anaesthesia of the lip and tongue) resulting from an intraoral injection of a local anaesthetic containing a vasoconstrictor. Phentolamine mesylate is a non selective, competitive, α-adrenergic antagonist that reverses the effects of extravasation of adrenergic agonists such as epinephrine. A submucosal injection of phentolamine mesylate after an injection of local anaesthetic with vasoconstrictor enhances the clearance of the local anaesthetic, by increasing blood flow in the injection area and accelerating recovery from soft tissue anaesthesia. Studies have shown a 55.6 reduction in median time for return of normal lip sensation and a 60 percent reduction in median time for return of normal tongue sensation. Use in pediatric patients less than 3 years of age or <15 kg (33 lbs) has not been established and thus its use is not recommended for patients in this category. In pediatric patients weighing between 15 kg and 30 kg, the maximum dose of phentolamine mesylate recommended is ½ cartridge (0.2 mg).

The recommended dose of phentolamine mesylate is based on the number of cartridges of local anaesthesia with vasoconstrictor administered:

Amount of Local Anaesthetic Adminstered Dose of Pheontolamine Mesylate (mg) Dose of Phenolamine Mesylate (cartridges)
¼ cartridge 0.1 ¼
½ cartridge 0.2 ½
1 cartridge 0.4 1
2 cartidges 0.8 2

The phentolamine mesylate should be administered following the dental procedure using the same location(s) and technique(s) (infiltration or block injection) employed for the administration of the local anaesthetic.12,13

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