Complications can be classified as generalized and localized and divided into early
and late.
5.7.1 Generalized complications
Psychogenic
The most common psychogenic complication of local anaesthesia is fainting. The
chances of this happening are reduced by sympathetic management and
administration of the anaesthetic to children in the semi-supine position.
Allergy
Allergy to local anaesthetics is a very rare occurrence, especially to the amide group
to which most of the commonly used dental local anaesthetics (such as lidocaine
(lignocaine) prilocaine, mepivacaine and articaine) belong. The only members of the
ester group of local anaesthetics routinely used in the United Kingdom are benzocaine
and tetracaine (amethocaine), which are available as topical anaesthetic preparations.
Allergy to other constituents of local anaesthetic cartridges may occur, for example,
metabisulfite a reducing agent which prevents oxidation of epinephrine. Allergy can
manifest in a variety of forms ranging from a minor localized reaction to the medical
emergency of anaphylactic shock. If there is any suggestion that a child is allergic to a
local anaesthetic they should be referred for allergy testing to the local dermatology or
clinical pharmacology department. Such testing will confirm or refute the diagnosis,
and in addition should determine which alternative local anaesthetic can safely be
used on the child. The majority of referrals prove to have no local anaesthetic allergy.
Children who are allergic to latex merit consideration as this material is included in
the rubber bungs of some cartridges. When treating such a child it is imperative to use
a latex-free cartridge. Details of which cartridges are latex-free can be obtained from
the manufacturers.
Toxicity
Overdosage of local anaesthetics leading to toxicity is rarely a problem in adults but
can readily occur in children. Children over 6 months of age absorb local anaesthetics
more rapidly than adults; however, this is balanced by the fact that children have a
relatively larger volume of distribution and elimination is also rapid due to a relatively
large liver. Nevertheless, doses which are well below toxic levels in adults can
produce problems in children, and fatalities attributable to dental local anaesthetic
overdose have been reported. As with all drugs dosages should be related to body
weight. The maximum dose of lidocaine (lignocaine) is 4.4 mg/kg. This is an easy
dose to remember if one notes that the largest 2% (i.e. 20 mg/ml) lidocaine
anaesthetic cartridges available in the United Kingdom are 2.2 ml, which means they
contain 44 mg of lidocaine. Thus a safe maximum dose is one-tenth of the largest
cartridge available per kilogram. If the 10th of a cartridge per kilogram rule is adhered
to then overdose will not occur. Prilocaine, the other commonly used local anaesthetic
drug in the United Kingdom, has a maximum dose of 6.0 mg/kg and as it is normally
presented as a 3% solution the rule is one-eleventh of the cartridge per kilogram.
When it is noted that a typical 5 year old weighs 20 kg it is easy to see that over-dose