The addition of a vasoconstrictor to a local anaesthetic solution allows a longer working time (by reducing the rate of loss of the anaesthetic solution to the general circulation) and a reduction of the dose necessary to achieve effective anaesthesia. It reduces the bleeding, which improves operator vision, and therefore quality of care. Local anaesthetics currently in use do not cause vasoconstriction, therefore a separate vasoconstrictor is commonly added. In current practice, adrenaline and felypressin are the vasoconstrictors most commonly used. Noradrenaline has previously been used; however, it has significant adverse effects, particularly increased blood pressure.

Information about the concentration of vasoconstrictors and the local anaesthetics they are used with is shown in Table 13.6.

Adrenaline used for dental procedures ranges in concentration between 1:80 000 and 1:300 000. It is a synthetic molecule with the same structure as endogenous adrenaline from the adrenal medulla. Synthetic adrenaline has the same effect as natural adrenaline (ie vasoconstriction of the skeletal muscle vessels, pupil dilation, bronchial dilation, skin vessel contraction).

Adrenaline is affected by heat and light. Consequently, cartridges should be stored as instructed by the manufacturers (which usually includes keeping them in a cool and dark place). It is recommended to use cartridges at room temperature. Some clinicians warm cartridges before use; if this is done, it is recommended that this occurs only immediately before use and not for a sustained period of time.

Dental local anaesthetics containing adrenaline are best not used for patients taking monoamine oxidase inhibitors (MAOIs) as MAOIs and adrenaline can adversely interact.

Felypressin is a vasoconstrictor based on the pituitary hormone oxytocin. This is used in doses of approximately 0.03 international units/mL, and at these doses has minimal myocardial effects. Its lack of effect on the central nervous system makes it useful where adrenaline is contraindicated (which is rare).

Felypressin is contraindicated during pregnancy as its similarity in structure to oxytocin (the hormone responsible for labour) can result in some contraction of the uterus.

At higher doses, felypressin may cause some coronary artery constriction.