Toxicity of Local Anesthetics in Man

Abstract

Signs and symptoms of toxicity causing alarming reactions and, on occasion, the death of the patient may accompany the use of local anesthetic agents in dentistry. The untoward reactions manifested by the dental patient may be due to the local anesthetic or vasoconstrictor used, or may represent a psychomotor response triggered by the patient’s fear of the impending procedure. If direct intravascular injections are avoided, there is little likelihood that local anesthetic agents, in the volume and concentration used in dentistry, will produce true systemic toxicity in normal subjects. In hypersensitive subjects, however, because of the rapid absorption from the highly vascular tissues injected, signs and symptoms of toxicity may follow the use of otherwise safe doses of local anesthetic agents. Allergic manifestations caused by local anesthetic agents may develop in patients with or without previous history of allergic disorders, either on the first or on repeated administration of a local anesthetic agent. Reactions to vasopressors may also be caused by the use of excessive doses in normal subjects, or by the use of normal doses in hypersensitive subjects. On occasion, it is difficult to determine whether the toxic manifestations are caused by the local anesthetic or vasopressor used or are of a psychogenic nature. The understanding of the basic anatomic and pharmacologic principles involved and strict adherence to precautionary measures developed on the basis of these principles will markedly diminish the severity and incidence of untoward reactions associated with the use of local anesthetic agents. The most important of these measures are: 1. The lowest concentration and the smallest volume of the least toxic local anesthetic agent capable of providing satisfactory operating conditions should be used. 2. The rate of systemic absorption of the local anesthetic agent should be decreased by the admixture of a suitable concentration of epinephrine or some other vasoconstrictor. 3. No smaller than a No. 25 needle should be used, and gentle aspiration in four planes should be carried out before injection of the local anesthetic agent to avoid intravascular injection. 4. The local anesthetic drug should be injected slowly. 5. With few exceptions, the concentration of vasopressors should not exceed 1:200,000 and in hypersensitive patients, concentration no higher than 1:400,000 should be used. 6. In selected cases, premedication with barbiturates may diminish the incidence and severity of reactions. When reactions occur, they must be treated promptly. This can only be done effectively if the dentist himself is capable of handling respiratory and circulatory emergencies, has the necessary drugs and equipment at his disposal and has his office personnel adequately trained in the performance of the specific tasks assigned to them in the case of an emergency. The most important prerequisite for successful resuscitation is prompt and efficient oxygenation. This should start at once. In severe intoxication, there is no time to wait for medical help. Adherence to the outlined principles will not only minimize the incidence and severity of toxic manifestations that may accompany the use of local anesthetic agents in dentistry, but will also result in the successful resuscitation of the patient when, despite all precautions, central nervous system or cardiovascular complications develop.