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The pressor effects of local anesthetics.

In the dental office, toxic reactions to local anesthetics are rare, but occasionally do occur. Responses to less than 50 mg of lidocaine have been reported. Investigators have attributed such a reaction to allergy, idiosyncrasy, or decreased tolerance, as well as other explanations. Drug toxicity primarily affects the central nervous system and cardiovascular system. Symptoms include dizziness, ringing in the ears, vague sensations of light-headedness, and nystagmus. Slight skeletal muscle twitching in the fingers and face are usually the first indications of local anesthetic toxicity. If blood levels rise higher, tonic and clonic convulsions may occur, followed by respiratory depression. One lesser known and studied effect of local anesthetics is their ability to increase blood pressure via central nervous system toxicity. Although in most cases it is not a tremendous increase, it has been explained experimentally and is not due to an idiosyncrasy of the patient. In one study done by Aldrete et al' baboons were injected with 3 mg/kg of lidocaine into the lingual artery. They showed that if administered under pressure a reverse flow occurred, forcing the local anesthetic into the internal carotid artery. This in turn sent toxic levels of local anesthetic in to the central nervous system. Another theory is that of sub-perineural centripetal spread. This theory proposes that a local anesthetic injected into the subperineural space, travels very rapidly in a centripetal direction to reach the brain.7 However, an injection into the sub-perineural space seems almost impossible. The next question to be answered is where in the central nervous system do the local anesthetic molecules act to cause an increase in blood pressure? Haranath and Bhatt3 showed that an increase in blood pressure occured when the cerebral ventricles of dogs were perfused with 10-40 mg of lidocaine. Perfusion with 0.1 percent lidocaine produced in about 10-15 minutes a rise in blood pressure of 20 mm Hg. On perfusion of 0.25 or 0.5 percent lidocaine, the blood pressure rose by 80-100 mm Hg by the end of the third or fourth minute and later declined. Therefore, this is a bi-phasic blood pressure response. This bi-phasic response has been shown