Articles: anesthetics.
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Anesthesia and analgesia · Nov 1976
Local anesthetic agents--pharmacologic basis for use in obstetrics: a review.
Because of the minimal effects on mother and fetus, regional anesthetic technics are widely employed for labor and delivery. However, the literature describes at least 35 fetal and neonatal deaths and a frightening incidence of fetal distress associated with paracervical block for 1st-stage labor. ⋯ Bupivacaine, a relatively new, long-lasting local anesthetic, is extemely toxic when administered paracervically, but no deaths have been reported with its use for epidural anesthesia. While choice of method and agent must be individualized, continuous lumbar epidural block with bupivacaine appears as effective as and less often dangerous to the fetus than paracervical block.
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In spite of the great advances in anesthesia, regional anesthesia has not lost its importance. The development of new, longer-acting local anesthetics has extended its indication still more. The causes of accidents lie mostly in ignorance ofthe pharmacology of local anesthetics and their adjuvants, in faulty technical performance of the nerve blockade and last but not least in inadequate knowledge of the therapy, of the side effects and complications. The various complications of regional anesthesia are reported on and the necessary therapy dealt with.
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Local anesthetics block nerve conduction by preventing the increase in membrane permeability to sodium ions that normally leads to a nerve impulse. Among anesthetics containing tertiary amine groups, the cationic, protonated form appears to be more active than the neutral form. However, the neutral forms, as well as uncharged molecules like benzocaine and the aliphatic alcohols, also depress sodium permeability. ⋯ The channel has a higher affinity for larger anesthetic molecules, but this may result from their greater hydrophobicity as well as from their size. The binding site favors molecules that contain more polar linkages between the amine group and the aromatic residue. Binding of amine anesthetics is weakly stereospecific and, surprisingly, shows no absolute requirement for the terminal alkyl ammonium moiety present in most local anesthetics...