General Anesthetic Drugs Used during Labor –Effects on the baby

General Anesthetic Drugs  –Effects on the baby

Neonatal drug depression is minimized by keeping drug dosage levels low in the mother and by keeping the induction delivery interval as short as possible. Avoiding aortocaval compression, hypotension or hypoxia in the mother ensures that the infant is not hypoxic.

                Maternal safety during general anesthesia remains unpredictable. The danger of inhalation of stomach contents, especially in patients undergoing emergency cesarean section, continues to be a significant cause of maternal death. For this reason conduction anesthesia for surgical delivery of patients in labor is gaining popularity. However, general anesthesia remains essential for a small number of obstetric patients.

                The intravenous induction agents that are in widespread use in obstetric anesthesia, thiopentone, methohexitone and althesin, cross placenta so rapidly that it is not possible to deliver the baby before some quantity of the drug has been transferred; detectable levels occur within 30 seconds of an intravenous dose. However, the newborn appears not to be affected with these levels since the drugs, after crossing the placenta from the umbilical vein, pass through the fetal liver where some is metabolized. /the drug level in the infant’s brain is further lowered by dilution with less contaminated blood from the fetal legs and abdomen. The drug concentration very rapidly declines in the mother after a single dose as the drug I redistributed throughout her circulation. This ensures that the level continues to fall in the fetus.

                Volatile anesthetic agents are generally added to the inspired mixture to ensure maternal unawareness. The halogenated agents, halothanes, methoxyflurane and enflurane allow the mother a 50% oxygen proportion in the inspired air and may improve uterine blood flow. These agents do not increase postpartum uterine bleeding unless used in very high doses. They do not depress the newborn.

                Muscle relaxants cross the placenta in clinically insignificant amounts; succinyl choline I very rapidly metabolized by the pseudocholinesterase in the mother’s plasma. The non-depolarizing. Longer acting relaxants are very large molecules that are highly ionized and so are unable to cross the placenta.

                Nitrous oxide used intermittently or continuously for pain relief in normal labor does not cause maternal cardiovascular depression or alters uterine contractility, and it is safe for the fetus in concentrations of up to 50% in inspired air. However, nitrous oxide ad oxygen, when used alone for cesarean section without supplementary inhalational agents, has resulted in neonatal depression. This is possibly caused by decrease uterine perfusion following high endogenous catecholamine levels that are associated with this very light anesthesia.

                The premixed cylinders of 50% nitrous oxide and oxygen have been shown to give considerable analgesia. But timing of administrations is not easy when they are used intermittently, and thus analgesia is less efficacious than continuously inhaled self- administered nitrous oxide.