Avoidance of the teratogenic effects of anesthetics on the neonate is paramount in caring for this population. One should also try to avoid derangement of neonatal homeostasis, which can be affected directly and indirectly by anesthetic drugs and techniques.
The teratogenic effect of anesthetic drugs is a very controversial issue that has no clear-cut answer. Exposure to anesthetic agents may be either acute during surgery-sedatives, hypnotics, narcotics, muscle relaxants, local anesthetics, oxygen and carbon dioxide, or inhalational anesthetics-or chronic because of occupational exposure to inhalational anesthetics.
Even though human studies of the effect of acute exposure of anesthetics demonstrated an increased incidence of spontaneous abortion, in women who underwent surgery during their first and second trimesters they failed to show any teratogenic effects on the fetus.
Several reports of increased congenital anomalies as well as spontaneous abortion among operating room personnel have been published. An important report regarding this issue was published by an ad hoc committee of the American Society of Anesthesiologists. They found an increased risk of congenital anomalies and spontaneous abortions in women working in operating room areas when compared with non-operating room female hospital employees.
Sedative and Hypnotic Agents
Barbiturates have been used in humans as induction agents for a long time. Although there is a conflicting report in animals regarding the teratogenic effect of barbiturates, in pregnant women these agents have been found to be safe. Phenothiazines have also been observed to be without any adverse effect in humans. Recent studies did not find any increased anomalies following use of diazepam. Midazolam has not been observed with any teratogenecity.
There is also no evidence that these opioids are associated with teratogenecity in humans.
There is no evidence of an adverse effect in fetal development following the use of muscle relaxants.
No evidence of teratogenecity was observed following the administration of benzocaine, procaine, tetracaine, or lidocaine. In contrast, the use of cocaine is associated with fetal congenital malformations both in humans and animals. This may be explained by cocaine-mediated vasoconstriction and, hence, fetal tissue hypoxia.
Oxygen and Carbon Dioxide
Hypoxia, as well as hypercarbia has been associated with teratogenecity in animal species. Although a high concentration of inspired oxygen at atmospheric pressure does not produce any adverse effects, hyperbaric oxygen exposure is associated with fetal anomalies in animals.
The addition of inhalational anesthetics such as nitrous oxide or halogenated agents to oxygen has become a routine practice when administering general anesthesia. Some of these agents have been implicated in the development of fetal anomalies as well as in premature births.
Nitrous oxide has been demonstrated to have teratogenic effect. The mechanism of teratogenecity following nitrous oxide exposure may not be related to interference in DNA synthesis but rather to a physiological effect of nitrous oxide, such as reduction in uterine blood flow due to increased sympathetic activity.
Halothane, enflurane, and isoflurane at physiological minimum alveolar concentrations are not associated with any teratogenecity in rats. Nor has evidence of teratogenecity been seen in humans with these agents. Recently a review article has been published related to drugs in pregnancy. The newer inhalation anesthetics sevoflurane and enflurane are not associated with any teratogenecity.