Special Considerations Anesthesia

As many as 2% of pregnant women in the United States undergo anesthesia for surgical procedures unrelated to delivery (35,36). Anesthetic management strategies focus predominantly on the alterations in maternal physiology from anesthesia. Although teratogenic effects of anesthesia may be of concern to patients and physicians, no anesthetic agents have been found to definitively cause fetal malformations (37).

Gravid patients normally experience a compensatory respiratory alkalosis with a PaCO2 ranging from 28 to 32 mmHg and a resultant pH of approximately 7.44 (38). Fetal PaCO2 is directly related to maternal PaCO2. With a rise in maternal PaCO2, fetal heart rate increases reflecting fetal distress (39).

Pregnant sheep models have been used to demonstrate that not only periods of severe hypercarbia (PaCO2>60 mmHg) but also severe hypocapnia (PaCO2<29 mmHg) reduce uterine blood flow leading to fetal distress (40). These changes have not been documented during laparoscopic surgery with appropriate anesthetic monitoring and maintenance of normal maternal pH.

Maintenance of uteroplacental blood flow is central to fetal well-being with fetal asphyxia resulting from a decrease in uteroplacental blood flow. The pharma-cologic agent of choice for maintaining maternal blood pressure is ephedrine. Other vasopressors such as alpha-agonists, dopamine, and epinephrine induce uterine artery vasoconstriction resulting in decreased uterine blood flow and should be avoided (38).

Other anesthetic considerations in the gravid patient are alterations in free drug concentrations as a result of expanded blood volume, low albumin, and increased alpha 1-glycoprotein. There is an increased risk of aspiration secondary to distortion of the gastric and pyloric anatomy from the gravid uterus and the hormonally induced decrease in lower esophageal sphincter tone (38).

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