Used During Labor –Effects on the Baby

Systemic Analgesics Drugs Used During Labor –Effects on the Baby

There is no single ideal analgesic agent for use in labor. All analgesic drugs cross the placenta and depress the fetus. The degree of depression will depend on the dose of the drug the length of time of exposure and the maturity and well- being of the fetus.

                Although the opiates are the most effective analgesic drugs available, their use in obstetrics is losing favor because of the depressant effect on the neonate, the effect of the mother’s psyche, making her less aware of her experience of childbirth, and because in doses that minimize side effects the pain relief is poor.            

                The most commonly used opiate in labor is pethidine, although diamorphine and fetanyl are also used. The maternal side effects of narcotics are dose related and include hypoventilation, postural hypotension, postural pypotension and loss of consciousness. Emetic effects of all opiates are also dose-related but this varies in individual paticents. Grastric motility is decrease by narcotics and stomach emptying may b de3layed for up to 12 hours. Opiates are reported to shorten labor, and correct in co-ordinate uterine action. But the mechanism appears to be the relief of pain and anxiety rather than any direction action of the uterine muscle.

                Placental transfer of all the opiates takes place rapidly and equilibration between maternal and fetal blood is completed within a short time. The effects of ethidine on the fetus that can be demonstrated in utero are a decrease in beat-to-beat variability on the cadiotocograph and altered fetal electroencephalogram. The neonatal effects of maternal opiates are a decrease Apgar score, a prolonged time to achieve regular respiration, lower oxygen saturation, decreased minute volume, hypercapnia and abnormal neurobehavioural scores. All these effects are related and can persist in the neonate for several days since the half-life of the opiates in the neonate is four to five times longer than that in the adult.

 Opiate effects and side effects can all be antagonized by naloxone –a pure opiate antagonist. There is no purpose in giving any combination of opiate plus antagonist to the mother in pain, as all the actions, including the analgesic action, will be reserved. If the mother has received opiates in labor naloxone should be given to those neonates who are depressed and do not breathe following initial resuscitation.

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.

Local Anesthetic Drugs -Effects on the Baby

Local Anesthetic Drugs Used During Labor –Effects on the Baby

Conduction anesthesia has become the most commonly used in modern obstetric practice, both to provide analgesia for labor pain and anesthesia for surgical delivery. Epidural blocks give a versatile range of anesthesia from a mild sensory block for normal labor to a dense blockade of most of the nerve fibers required for cesarean section.

                The local anesthetics commonly used for obstetrics are bupivicaine and lignocaine. When injected, these drugs are absorbed from the epidural space into the maternal blood stream. This results in a significant level of circulating drug which will cross the placenta rapidly by passive diffusion. Many factors affect the placental transfer such as the total dose of drug injection, route of administration, presence of adrenalin, maternal metabolism and exertion, maternal protein binding and intervillous blood flow. These factors determine the fetal-to-maternal concentration ratio. Pathological conditions of the placenta such as eclampsia, diabetes, hyper-tension, and Rhesus disease may also affect this transfer but the extent to which they do so is unknown. The local anesthetic is taken up by the fetus and metabolized and excreted by the baby. Similar, though delayed, decay curves of drug activity are a seen in neonatal and maternal circulations.

                Local anesthetics act on all conduction tissue and toxicity in the fetus and neonate is seen in the central nervous system, peripheral blood vessels and the heart. No fetal heart rate changes occur at modest plasma levels of local anesthetic.

                Conduction anesthesia also has indirect effects on the fetus, which requires an adequate delivery of oxygenated maternal blood to the intervillous space. This can be affected by changes in the uterine blood flow, which varies directly with perfusion pressure across the uterine vascular bed, and in aversely with uterine vascular resistance. So, if hypotension results from an epidural block, a reduction in mean uterine pressure will reduce uterine blood flow and thereby impair fetal oxygenation and well-being. Hypotension is a common complication of epidural block, especially at term when pooling of blood in the lower limbs in encouraged not only by sympathetic blockade but by aortocaval compression.

                Uterine vascular resistance is maintained by the intrinsic vasomotor state of uterine vessels. These are fully dilated at term but ill constrict with high catecholamine levels, general anesthesia and toxic levels of local anesthetic drugs.

Antibiotics in Pregnancy

Antibiotics in Pregnancy

Antibiotics which are safe for pregnancy penicillin, erythromycin clindamycin cephalosporins.

Prophylactic Antibiotics

Ampocillin, amoxicillin, cefazolin, and erythromycin/sulbactam are the safest drug to treat the preterm premature rupture of membrane, prevention of bacterial endocarditis and during cesarean section, urinary tract infection, chorio-amnionitis and group B streptococci.

Antibiotics to be avoided

Following drugs to be avoided:

Ø  Amino glycosides = eight cranial nerve damage

Ø  Erythromycin estolate = hepatotoxic to mother

Ø  Fluoroquinolones = potentially mutagenic, cartilage damage, arthopathy, teratogenicity

Ø  Ribavarin = possibly fetotoxic

Ø  Tetracyclines = staining of deciduous teeth.