Catálogo de publicaciones - libros

Parturients undergo remarkable changes during pregnancy, labor, and the immediate postpartum period that can directly affect anesthetic techniques; hence a broad knowledge of these changes is essential for proper management of these women.

Local anesthetics are an integral part of obstetric anesthesia; hence an adequate knowledge of these chemical agents is absolutely essential.

Perinatal pharmacology involves the three most important participants in pregnancy: the mother, the placenta, and the fetus (Fig 3-1). There are only a few drugs (heparin, protamine) used in parturients that cannot traverse the placenta and go to the fetal side. Therefore, most of the drugs used in pregnant Figure 3-1 Drug disposition in the mother, placenta and fetus. women will affect the fetus to a certain extent; hence perinatal pharmacology should be an important part of obstetric anesthesia.

Newer pharmacological agents are being used more frequently for the treatment of maternal and fetal pathological states. Obstetric anesthesiologists should be aware of the interactions of maternally administered drugs with anesthetic agents and techniques.

Maintenance of uteroplacental blood flow is the hallmark for fetal well-being; hence an in-depth knowledge of this subject is essential for individuals taking care of pregnant women.

Labor and delivery are complex processes involving different organ systems orchestrated in expelling the fetus and placenta from the mother. This process has been divided into three specific stages: 1. The first stage starts from the latent phase of labor (progressive cervical dilatation associated with regular uterine contraction) and terminates at the time of full dilatation of the cervix. 2. The second stage starts from full dilatation of the cervix and terminates at the time of the delivery of the infant. 3. The third stage starts from delivery of the infant and terminates at the time of expulsion of the placenta.

Systemic medications have been used exclusively or in association with psychoanalgesia for relief of labor pain during both the first and second stages of labor. These drugs can be classified in the following manner: 1. Narcotics 2. Sedatives and/or tranquilizers 3. Dissociative medications 4. Amnestic drugs 5. Neuroleptanalgesia 6. Agonist-antagonist medications

Subarachnoid and epidural opiates have become extremely popular for pain relief for both labor and delivery as well as cesarean section. Interestingly, spinal opioids have physicochemical properties very similar to local anesthetics , 1 as shown in Table 8-1. Low pKa and high lipid solubility will be associated with a rapid onset of pain relief, whereas low lipid solubility, because of higher concentrations of drug in the cerebrospinal fluid (CSF), will increase the chance of delayed respiratory depression (morphine) . The site and mechanism of action are different. Presynaptic and postsynaptic receptors in the substantia gelatinosa of the dorsal horn of the spinal cord have been cited as the major site of action for spinal opiates, 1 whereas blockade of the axonal membrane of the spinal nerve roots and of the anterior and posterior horn cells is the mechanism of action for local anesthetics. Consequently, spinal opiates can produce “selective” blockade of pain without blocking the sympathetic nervous system and thus can maintain a stable cardiovascular system .

Apgar scores and neonatal acid-base values at the time of delivery used to be the main criteria to evaluate the effects of maternally administered drugs on neonates. Neurobehavior tests have become popular in recent years to observe subtle changes as well as the delayed effect of maternally administered medications. Various neurobehavioral examinations used include: the Graham-Rosenblith scale, 1 the Prechtl-Beintema neurological examination, 2 the Bayley scales, 3 the Brazelton neonatal behavioral examination, 4 the Scanlon early neonatal neurobehavioral scale (ENNS), 5 and the Amiel-Tison/Barrier/Shnider (ABS) 6 neurological and adaptive capacity scoring system. Although based on the Prechtl-Beintema 2 neurological examination, the Brazelton neurobehavioral examination is one of the most thorough tests existing at the present time. The state of consciousness is recognized before evaluation of each item, and habituation to different stimuli is an important part of this examination. However, one of the disadvantages of Brazelton’s examination 4 is that it takes 45 minutes to complete the evaluation when performed by an experienced person.

One of the most important goals for the anesthesiologist caring for a pregnant women should be to maintain the uteroplacental unit and fetus in optimal condition. Hence, an adequate knowledge of uterine activity and fetal monitoring is important. Different devices are used for the intrapartum assessment of uterine activity as well as fetal well-being.