a. Precautions should be taken against the danger of confusing the various agents with one another or mistaking different concentrations of the same drug.
b. In order to avoid intravascular (into the veins) injection, aspiration in several planes with the plunger of the syringe should always be done before injecting the anesthetic solution into the tissues.
c. The instillation of local anesthetic agents into the trachea and bronchi leads to immediate absorption, which soon reach blood levels comparable to those reached by straight intravenous injection.
d. A previously punctured vial of local anesthetic solution should never be re-autoclaved.
e. Discolored local anesthetic solutions should be immediately thrown away. 4-6. TOXICITIES OF LOCAL ANESTHETICS
Essentially all systemic toxic reactions associated with local anesthetics are the result of over-dosage leading to high blood levels of the agent given. Therefore, to avoid a systemic toxic reaction to a local anesthetic, the smallest amount of the most dilute solution that effectively blocks pain should be administered.
a. Hypersensitivity. Some patients are hypersensitive (allergic) to some local anesthetics. Although such allergies are very rare, a careful patient history should be taken in an attempt to identify the presence of an allergy. There are two basic types of local anesthetics (the amide type and the ester type). A patient who is allergic to one type may or may not be allergic to the other type.
b. Central Nervous System Toxicities. Local anesthetics, if absorbed systematically in excessive amounts, can cause central nervous system (CNS) excitement or, if absorbed in even higher amounts, can cause CNS depression.
(1) Excitement. Tremors, shivering, and convulsions characterize the CNS excitement.
(2) Depression. The CNS depression is characterized by respiratory depression and, if enough drug is absorbed, respiratory arrest.
c. Cardiovascular Toxicities. Local anesthetics if absorbed systematically in excessive amounts can cause depression of the cardiovascular system. Hypotension and a certain type of abnormal heartbeat (atrioventricular block) characterize such depression. These may ultimately result in both cardiac and respiratory arrest.
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