Pregnant patients present a unique challenge to anesthesiologists. These patients are medically complex, requiring the anesthesiologist providing care to possess a thorough understanding of both the changes in physiology and subsequent pharmacology of the parturient. Providing obstetric anesthesia has always come with an increased risk when compared to other patient populations of similar age, and the combination of women having children later in life along with women with congenital heart defects attempting to conceive has made providing anesthetic management for these patients increasingly complicated.
Every major organ system is affected by pregnancy, yet the major physiological consideration the anesthesiologist must be aware of are the effects that pregnancy has on the cardiovascular system. From a volume standpoint, pregnant patients experience an approximate 50% increase in intravascular volume peaking mid third trimester. In addition to increases in volume, there is a decrease in systemic vascular resistance that progresses throughout pregnancy which accommodates for a 30-40% increase in cardiac output that also occurs during this time. The combination of increased volume and cardiac output results in increased cardiac oxygen requirements that can result in maternal cardiac arrest if vigilance is not maintained in the OR. Lastly, pregnancy is associated with hypercoagulability secondary to reductions in Protein S as well as increases in factors VII and fibrinogen. While hypothesized to be a natural protection against hemorrhage during and after the delivery process, this hypercoagulable state places the parturient at a 100-fold risk of developing a venous thromboembolism further increasing the risk of providing anesthesia. In addition to the cardiovascular system, other major physiological considerations the provider must be aware of come from a pulmonary/airway management standpoint. These latter considerations concern the effects pregnancy has on reductions in functional residual capacity and increased oxygen consumption, as well as the increased risk of aspiration secondary to delayed gastric emptying. These physiological considerations result in four major principles of basic obstetric anesthesia management. First, the anesthesiologist must ensure adequate uteroplacental perfusion. Second, maximizing pain control while minimizing high sympathetic blockade. Third, providing ASA standard monitoring to the patient as well as being able to interpret fetal monitoring. Fourth, ensuring a patent airway by providing aspiration prophylaxis and necessary airway intervention subject to the type of surgery being performed.
While complicated, successful anesthetic management of the parturient is possible, but is contingent on the anesthesiologist having a comprehensive understanding of the physiological changes associated with pregnancy, a working understanding of the procedures that the patient is likely to undergo, and a strong ability to coordinate with the obstetrician as well as any specialists involved in the patient’s care prior to the operating room.