What are the maternal and fetal physiological considerations that should be taken into account prior to beginning this procedure?

How do you maintain fetal well-being during the course of the procedure? What are the primary considerations for maintaining adequate blood flow?

How would you prepare the patient(s) for surgery and anesthesia? What kind of monitors should be in place?

What is the normal fetal oxygen saturation? How would you monitor heart function?

Pregnancy affects many aspects of maternal physiology. Oxygen demand is greater so precautions must be taken to prevent periods of prolonged apnea or hypoventilation. Capillary permeability increases so the risk of pulmonary edema is elevated – particularly in the setting of magnesium used for tocolysis. The weight of the gravid uterus can decrease venous return so left uterine displacement is an important consideration. In terms of the fetus, exposure to stress has been associated with increased cortisol and other stress hormones. Opiates have been shown to attenuate this response – so there is no doubt about the need for anesthesia in the fetus. The fetus requires less anesthesia than a child, but it should be recognized that although inhaled agents readily cross the placenta, they do not reach maternal levels for a prolonged period of time. The fetal heart has less contractile tissue and is sensitive to the cardiac depressant effects of anesthesia. When combined with fetal manipulations during surgery, hypotension, bradycardia, and cardiovascular collapse are a significant consideration. The circulating volume of a fetus is very small and blood loss is poorly tolerated. Fetal skin is not yet mature and subcutaneous tissue is lacking – thus leading to the tendency for hypothermia if exposed to ambient temperature environment for any period of time.

Fetal circulation is dependent on uteroplacental blood flow. Maternal volume status and blood pressure must be optimized. Uterine tone increases during contractions with a corresponding increase in vascular resistance. It is therefore critical to keep the uterus relaxed. Kinking of the umbilical cord must be avoided and corrected if it occurs. Increased pH and hypocarbia will decrease uterine blood flow and result in fetal hypoxia.