Complications with Local Anæsthetics
Incorrect Placement

Injection of Local Anæsthetic within the Parotid Gland can lead to a temporary
facial palsy (that is, a temporary paralysis of the muscles of facial expression).  
Although alarming, no permanent damage occurs and the patient should make a
full recovery.  An eye patch may be required until normal eyelid closure returns as
the eye can be prone be being irritated by dust particles.

Chewing Muscle Injury (Trismus)

This may result in painful muscle spasm leading to limitation in mouth opening
trismus).  This usually resolves spontaneously.

Adjacent Vascular Structures

These may be injured, resulting in a local blood clot.  This may be seen following
injections to ‘numb up’ lower jaw teeth as the
Inferior Dental Nerve has in close
proximity to it, the corresponding artery.  Bleeding results in limitation of mouth
opening (

Toxic Symptoms

Local Anæsthetic may be injected directly into the circulation.  This may lead to
rapid onset of toxic symptoms which can result in collapse and cardio-respiratory
arrest.  You may experience a mild form of this as a racing heart, tremor and a
sense of impending doom.  Rapid injection into the tissues by itself may also lead
to toxicity.

Infected Tissues

Local Anæsthetic should not be injected into inflamed or infected tissues.  The
locally inflamed +/- infected circulation may lead to rapid absorption of the
.  In addition, the acid environment associated with infection reduces
the effectiveness of the
Local Anæsthetic.

Hypersensitivity-Type Reaction

These can sometimes occur with some Local Anæsthetics but they are extremely
rare (often the preservatives and not the anaesthetic itself).

Needle Track Infection

This is where infection ascends the path of the injection.  This can lead to a
limitation in mouth opening (
trismus).  It is very rare.

Post-Injection Problems

The patient must be aware to avoid smoking, drinking hot liquids or biting the lip,
cheek or tongue until sensation has fully returned.

Useful Article:

JADA 2003.  Avoiding complications in local anesthesia induction. Anatomical
Last Updated 7th September 2012