can easily occur unless care is exercised. The use of vasoconstrictor-containing local
anaesthetics for definitive local anaesthesia is recommended in children, as agents
such as epinephrine (adrenaline) might reduce the entry of local anaesthetic agents
into the circulation. In addition, as vasoconstrictor-containing solutions are more
effective, the need for multiple repeat injections is reduced.
CARDIOVASCULAR EFFECTS
Cardiovascular effects caused by the injection of a dental local anaesthetic solution
will be due to the combined action of the anaesthetic agent and the vasoconstrictor.
Local anaesthetics affect the cardiovascular system by their direct action on cardiac
tissue and the peripheral vasculature. They also act indirectly via inhibition of the
autonomic nerves that regulate cardiac and peripheral vascular function. Most local
anaesthetic agents will decrease cardiac excitability, and indeed lidocaine (lignocaine)
is used in the treatment of cardiac arrhythmias. Both vasoconstrictors commonly used
in the United Kingdom, namely epinephrine (adrenaline) and felypressin, can
influence cardiovascular function. In addition to the beneficial effect of peripheral
vasoconstriction for surgical procedures, epinephrine has both direct and indirect
effects on the heart and the doses used in clinical dentistry will increase cardiac
output, although this is unlikely to be hazardous in healthy children. Felypressin at
high doses causes coronary artery vasoconstriction, but the plasma levels that produce
this are unlikely to be achieved during clinical dentistry.
CENTRAL NERVOUS SYSTEM EFFECTS
The fact that local anaesthetic agents influence activity in nerves other than peripheral
sensory nerves is obvious to any practitioner who has inadvertently paralyzed the
peripheral branches of the motor facial nerve during an inferior alveolar nerve block
injection. Similarly, the central nervous system is not immune to the effects of local
anaesthetic agents. Indeed, plasma concentrations of local anaesthetics that are
incapable of influencing peripheral nerve function can profoundly affect the central
nervous system. At low doses the effect is excitatory as central nervous system
inhibitory fibres are blocked, at high doses the effect is depressant and can lead to
unconsciousness and respiratory arrest. Fatalities due to local anaesthetic overdose in
children are generally due to central nervous tissue depression.
METHAEMOGLOBINAEMIA
Some local anaesthetics cause specific adverse reactions when given in overdose.
Prilocaine causes cyanosis due to methaemoglobinaemia.
In methaemoglobinaemia the ferrous iron of normal haemoglobin is converted to the
ferric form which cannot combine with oxygen.
TREATMENT OF TOXICITY
The best treatment of toxicity is prevention. Prevention is aided by: (1) aspiration; (2)
slow injection; (3) dose limitation. When a toxic reaction occurs then the procedure is:
(1) Stop the dental treatment. (2) Provide basic life support. (3) Call for medical
assistance. (4) Protect the patient from injury. (5) Monitor vital signs.
Drug interactions
Specialist advice from the appropriate physician should be requested in the treatment