Articles: anesthetics.
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Local anesthetics are in general not suitable for the treatment of patients with severe cancer pain. Local blocks are useful for diagnostic and prognostic purposes. ⋯ The use of local anesthetics may yield long-lasting relief in some specific pain syndromes, such as tumor-related reflex dystrophies, in painful muscle spasms, and trigger points due to tumor-affected vertebrae. In addition, local anesthetics may have a generally beneficial effect in the restless, cachectic, and aged patient.
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This review includes a brief discussion of the indications and pitfalls of regional anaesthetic techniques commonly used during parturition. Emphasis is given to the physiological changes of pregnancy and the potential effects on the fetus. The criteria for the choice of local anaesthetic are also presented.
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The clinically useful local anesthetic agents can be divided chemically into the amino-esters, e.g., procaine, chloroprocaine and tetracaine, and the amino-amides, e.g., lidocaine, mepivacaine, prilocaine, bupivacaine and etidocaine. Pharmacologically, these agents can be categorized as agents of low potency and short duration of action, e.g., procaine and chloroprocaine; agents of intermediate potency and duration of action, e.g., lidocaine, mepivacaine and prilocaine; and agents of high potency and long duration, e.g., tetracaine, bupivacaine and etidocaine. The blood level of local anesthetics is determined by the rate of uptake, tissue redistribution, metabolism and excretion. ⋯ Among the ester agents chloroprocaine is cleared most rapidly due to its fast rate of hydrolysis. Within the amide series, prilocaine is cleared most rapidly due to its fast rate of tissue redistribution and its rapid hepatic metabolism. Bupivacaine is cleared most slowly due primarily to its decreased rate of hepatic degradation.
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Treatment with drugs and exposure to many environmental chemicals results in enzyme induction. However, the clinical significance of increased (or altered) metabolism of the inhaled anaesthetics appears to be trivial. Enzyme induction does not affect the conduct of inhalation anaesthesia. ⋯ Whether induction of halothane biotransformation and the production of reactive intermediates may lead to hepatoxicity is not yet settled. It is quite clear that induction, in the presence of hypoxia, leads to hepatic necrosis in rats. However, a similar relationship has not been established in surgical patients.