The most frequently used drugs in dentistry are local anaesthetics, either plain or in combination with a vasoconstrictor. Their side effects are likely to be the cause of many of the emergencies encountered by dentists. Certain precautions should always be taken when they are used. Below are listed the toxic manifestations of each agent, but it should be remembered that some of the effects of the base will be masked by the vasoconstrictor.
In practice it would seem that the commonest side effects seen are those due to adrenaline or nor-adrenaline. If the warning signs associate: with these toxic effects are not appreciated and administration ceased, there I is a high risk that the patient will collapse.
Adverse and toxic effects are determined by:
- Concentration and volume of solution.
- Rate of injection.
- Toxicity of agent.
- Presence or absence of vasoconstrictors.
- Physical status of the patient and his or her current drug therapy.
The major cause of systemic reactions is a high blood level of local anaesthetic base or vasoconstrictor. The aim must be to use the smallest volume of lowest concentration to achieve satisfactory anaesthesia.
In order to avoid these effects, the following precautions should be taken:
An adequate patient history should be taken. Certain diseases or the concurrent use of some drugs accentuate the undesirable side effects of adrenaline or nor-adrenaline.
Their use is absolutely contra-indicated in the following conditions:
1. Sensitivity to catecholamines.
2. Thyrotoxicosis – Their use is also contra-indicated where the patient is receiving the following drugs:
2.1. Sympathomimetic agents
2.2. Tricyclic antidepressant drugs, MAOI inhibitors.
2.3. Certain general anaesthetic agents (halothane, chloroform, trichlorethylene).
In these conditions felypressin (octapressin) is a safe alternative vasoconstrictor to adrenaline and nor-adrenaline, and may be used in circumstances where adverse reaction to these drugs is anticipated. Felypressin is the vasoconstrictor of choice should one be required in patients with cardiovascular disease and hypertension.
Aspiration Prior to Injection
Aspiration should always be performed prior to injection of any local anaesthetic solution. The toxic effect of both local anaesthetic and vasoconstrictor are increased where they are injected intravenously, so aspiration should always be performed prior to injection.
Inadvertent intravenous injection may occur not only with mandibular and maxillary block injections, but also in infiltration of both facial and palatal sites. An adequate aspirating syringe with a needle no finer than 26 gauge should be used for all injections and at least 2 seconds should be allowed for the aspiration.
Rate of Injection
Injections should be undertaken slowly, ideally at the rate of 1 mL per 30 seconds, to minimise possible toxic effects. Patients in the Sutherland Shire should be monitored for toxic effects which may occur occasionally at relatively low doses in susceptible persons.
Local Anaesthetic – The maximum dose of local anaesthetic base should be calculated from the weight of the patient particularly in infants and children. The maximum dose will depend on whether the local anaesthetic is plain or has vasoconstrictor added, as the latter will lessen the rate of absorption of the base.
Catecholamines - Clinically effective vasoconstriction for dental anaesthesia can be obtained with concentration in the range of 1:300 000 (3.3 ug/mL) adrenaline to 1:100 000 (10.0 ug/mL), and in order to minimise toxic effects the lowest effective concentration should be used. Where adrenaline is used a concentration of 1:80 000 (12.5 ug/mL) should not be exceeded and where nor-adrenaline is used a maximum of1:50 000 (20.0 ug/mL) is suggested.
Sedatives, Hypnotics and Analgesics
Sedative – A drug which allays apprehension, but does not produce analgesia.
Hypnotic – A drug which induces sleep, but does not produce analgesia.
Analgesic – A drug which reduces the patient’s perception of pain.
The response to hypnotic drugs is dose dependent and many hypnotics given in small doses will act as sedatives. Long-continued use of depressant drugs produces tolerance to the psychic effects of sedative drugs. Caution is always needed because metabolic disturbances or drug interaction may lead to depression of respiration which may, in turn, permit respiratory obstruction and respiratory failure as well as circulatory depression. As well as the specific sedatives and hypnotics, all tranquillisers, some antihypertensive drugs, antidepressant and antihistamines may have sedation as a side effect.
Unless pain is first controlled by analgesics or narcotics, the administration of sedatives will cause restlessness.
Pain may be controlled by:
- Analgesic drugs.
- Narcotics, which may induce sleep as well as relieve pain.
- General anaesthesia, which implies freedom from pain, produced by rendering the patient unconscious. Analgesics may be administered orally, by injection or by inhalation. They may be divided into two groups:
- Mild analgesics which act peripherally.
- Potent analgesics which exert a depressing action on the central nervous system.
Read More »