Advanced Techniques and Local Anesthesia
Complications from Local Anesthesia
Complications from local anesthesia are often due to overdosage. Predisposing factors, such as the patientŐs age, weight, state of health, and other medications that the patient may be taking (including meperidine, phenytoin, quinodine and desipramine, which is a tricyclic antidepressant) may cause increased free local anesthetic blood levels due to a lack of plasma proteins available for binding. During administration, both the rate of injection and the route of administration can also have an impact on the dosage effect, as rapid injection can lead to increased plasma levels of local anesthetic.
Drug factors may also be related to overdosage. The concentration of the local anesthetic in the blood supply may be increased due to the vasodilating activity of the local anesthetic; for this reason, a vasoconstrictor is often present with many of these agents. In addition, inadvertent intravascular injections can also cause toxic manifestations.
Overdose symptoms may be minimal to moderate, such as apprehension and excitability; however, as the level of local anesthetic in the blood increases, more serious effects may result including CNS depression, tonic-clonic seizures, and possibly respiratory and cardiovascular collapse. For a dosage of 40 to 160 mg of local anesthetic administered, the blood level rises to 1 µm/mL. CNS toxicity occurs at four times that amount, so there is a good therapeutic range. Fortunately most toxic reactions are mild and are self-limited, as cerebral blood levels of the anesthetic decrease over time with redistribution. With the toxic side effects of local anesthetics it is important to support the airway when needed and to perform basic life support as necessary.
Post-anesthetic intraoral legions may also develop, but will usually heal with time.
Persistent localized paresthias or anesthesias may also occur, most frequently as a result of direct trauma to a nerve; injection of the local anesthetic into the nerve sheath may result also in trismus or possible hematoma formation.
Infection, especially a needle track infection, which manifests itself pretty late, can occur. To prevent infection it is recommend that needles not be reused in a patient's mouth. Fresh needles should always be used, and the area to be penetrated should be cleaned prior to insertion of the needle.
Complications from Nerve Block
Facial nerve paralysis may occur temporarily with a nerve block. Again, reassure the patient that the condition will disappear as the anesthetic agent is metabolized.
Complications resulting from a maxillary nerve block are rare, but may include:
- regional sixth nerve block, results in temporary teplopia for the patient
- hematoma (rare)
- retrobulbar block (rare)
- optic nerve block, which can result in temporary blindness (rare)