Pregnancy and Anesthesia Considerations

Literature demonstrates that anywhere from 0.2 – 2.2% of pregnant women undergo non-obstetric surgeries and anesthesia per year [1, 2]. The decision to proceed with surgery and anesthesia during pregnancy requires special attention to several maternal adaptations that occur during pregnancy, including changes in maternal blood volume and cardiac output, alterations in acid-base and respiratory status, increased hypercoagulability, reduced lower esophageal sphincter tone, increased gastric volume and acidity, and increased sensitivity to opioids and inhalation agents [2]. In addition to physiological changes, actual timing of surgery in relation to trimester matters significantly for reducing poor fetal outcomes [1-3].

With respect to timing, it is commonly accepted that surgery during the first trimester should be avoided unless emergent [1-3]. Most researchers and practitioners advocate for surgery and anesthesia during the third trimester due to the completion of organogenesis by this period [1-3]. However, a 16-year retrospective, matched case-control, cohort study by Devroe et al., which examined the use of anesthesia for non-obstetric operations, demonstrated increased incidence overall of preterm births in the surgical group and increased risk of preterm birth secondary to surgery in the third trimester. Within the surgical group, the study did not find significant associations between the overall incidence of preterm births and the trimester during which surgery was performed.

Timing aside, another factor to consider is the use of general vs. regional anesthesia. The common consensus is to use local anesthesia whenever possible, in order to avoid systemic transfer of the anesthetic to the fetus. Kuczkowski 2004 explains that virtually every drug and inhalation anesthetic is considered teratogenic to some fetuses under certain conditions, and thus, there is no “best” anesthetic agent to use. He also highlights that the commonly deployed nitrous oxide (NO) has been shown to oxidize vitamin B12, and interfere with tetrahydrofolate regeneration and DNA synthesis. Some studies have experimented with using B12 and folic acid prophylaxis when using NO in pregnant women, however the benefit of doing so is not clinically apparent.

A contrasting opinion on NO use can be found in Ramirez et al.’s paper, which argued that nitrous oxide is a weak teratogen whose reproductive effects only occur after prolonged exposure and high concentrations, conditions unlikely to be met in pregnant women undergoing surgery. However, Devroe et al.’s study demonstrated a statistically significant increase in low birth rates in women exposed to general anesthesia, which often included the use of NO. The differences in opinions in these studies highlight the ongoing discourse surrounding the use and safety of anesthesia in pregnancy, however, medical professionals should always choose anesthetics with the highest track record of safety in pregnant women and optimize their use during surgery.

Finally, as aforementioned in the first paragraph, the physiological changes that happen during pregnancy are many and can complicate routine surgery. For these reasons, it is important to closely monitor parameters such as blood pressure, heart rate, oxygenation and respiratory status intraoperatively to avoid maternal and/or fetal complications [3]. Aortocaval compression is of particular concern during surgery, as pregnant women positioned on their backs can suffer bouts of decreased blood pressure and cardiac output secondary to inferior vena cava compression. The decrease in blood pressure can lead to decreased placental perfusion, hypoxia, and fetal acidosis and poor fetal outcomes. Fetal heart rates (FHR) have been shown to decrease in hypoxic environments and can thus serve as a useful gauge of hypoxia intraoperatively [3]. Lastly, because the stress of surgery can cause premature contractions, deployment of a tocodynamometer can be a valuable asset during surgery. All in all, though complicated and multifactorial, surgery during pregnancy is sometimes necessary and requires thorough planning and safety optimization.

References 

1. Devroe, S., Bleeser, T., Van de Velde, M., Verbrugge, L., De Buck, F., Deprest, J., … & Rex, S. (2019). Anesthesia for nonobstetric surgery during pregnancy in a tertiary referral center: a 16-year retrospective, matched case-control, cohort study. International journal of obstetric anesthesia, 39, 74-81.DOI:10.1097/01.aoa.0000661412.51134.86 

2. Ramirez, V., Valencia, G., & Catalina, M. (2020). Anesthesia for nonobstetric surgery in pregnancy. Clinical obstetrics and gynecology, 63(2), 351-363. DOI:10.1097/GRF.0000000000000532

3. Kuczkowski, K. M. (2004). Nonobstetric surgery during pregnancy: what are the risks of anesthesia?. Obstetrical & gynecological survey, 59(1), 52-56. DOI:10.1097/01.OGX.0000103191.73078.5F