Local Anesthetic Considerations When Treating Patients with Oral Infections

Products of inflammation lower the surrounding tissue pH (e.g., purulent exudates have a pH of 5.5-5.6). At this more acidic pH, the numbers of base molecules necessary for passage of the anesthetic into the nerve membrane may be significantly reduced. Inflammatory exudates may also enhance nerve conduction action potentials, making blockage of sensory nerve impulses more difficult. In addition, blood vessels in the area of inflammation may be dilated, leading to a more rapid uptake of the anesthetic agent from the area of injection. These changes can lead to delays in onsets of anesthesia, inadequate depths of anesthesia, and the potential for local anesthetic blood levels to be elevated. 

Needle tract infection is a potential complication of injection into infected tissues. Although penetration into infected tissues can be avoided by using more distant regional nerve blocks, whenever there is a possibility of a needle having passed through infected tissues, it should be discarded immediately after use to prevent inadvertent reuse.

Severe trismus is sometimes seen in inflammation and infection. Trismus has been mentioned previously as a painful condition that impairs the extension of the muscles of mastication leading to decreased ability to fully open the mouth. Limitation in opening can follow trauma, local anesthetic injections, and temporomandibular joint problems and ankylosis.

Limited opening can pose anatomical difficulties with standard conventional inferior alveolar (IA) nerve block techniques and especially with the Gow-Gates approach, which requires patients to open fully. In situations of severe trismus, an extraoral nerve block or an intraoral high nerve block technique (Vazirani-Akinosi) where the mouth remains closed during its administration is recommended.

Another serious concern with more severe progressive infections, such as Ludwig's angina, is the potential for airway compromise. Management and control of the airway is the first priority in these situations. These patients are typically treated with a general anesthetic in a hospital setting. Before induction of general anesthesia, airway management is initiated with conscious fiberoptic intubation or a possible surgical airway. In this setting, supplemental local anesthesia is administered once the airway is secure.

The effectiveness of local anesthesia in the presence of infection is frequently compromised by changes in tissue pH. The following suggestions may increase successful anesthesia outcomes:

• Allow additional time for the local anesthetic to take effect.

• Use a greater amount of local anesthetic to help overcome acidity created by the infection. (Make sure that maximum doses are not exceeded.)

• Use a regional nerve block away from the area of inflammation.

• Discard the needle after penetrating in or near an area of inflammation/infection.

• Consider potential secondary innervations to the area (e.g., mylohyoid nerve in the mandible).

• Use a local anesthetic agent with a higher pH.

• Alkalinize the local anesthetic by adding sodium bicarbonate immediately before the injection.*

• Use intravenous sedation or general anesthesia.

• If the infection is minor, consider antibiotics and rescheduling.

*Sodium bicarbonate decreases the acidity of the anesthetic solution and the tissues into which it is injected, providing significantly greater numbers of initial base molecules than were provided in the manufactured solution. Alkalinizing (buffering) local anesthetics with sodium bicarbonate has been difficult and inconvenient when only sterile, sealed cartridges are available.