Chapter 20: Nonobstetric Surgery During Pregnancy

BACKGROUND

Nonobstetric surgery during pregnancy is common and occurs in between 0.3% and 2.2% of pregnancies. Retrospective human studies have not conclusively shown that any anesthetic agent results in increased congenital abnormalities. The conclusions of past studies have suggested possible teratogenic effects associated with nitrous oxide and benzodiazepines. However, more recent large retrospective studies have not supported these findings. General timing principles include¹:

When a decision for surgery has been made, it is essential to begin planning and coordination. Early communication with obstetricians is important to ensure appropriate pre-, post-, and possible intraoperative fetal heart rate (FHR) monitoring is available. Prior to 22 to 24 weeks, only pre- and postoperative FHR monitoring is typically performed. Intraoperative monitoring is typically reserved for after the age of viability (>24 weeks) and may not be performed based on obstetrician and patient discretion. If intraoperative monitoring is performed, additional resources must be in place to allow for urgent or emergent cesarean delivery.

Necessary additional resources include:

• A labor and delivery nurse in the operating room (OR) to monitor the FHR and an obstetrician be available on standby to interpret the FHR and perform cesarean delivery.

• A cesarean delivery surgical tray needs to be in the OR at the start of the case along with neonatal resuscitation equipment, including a neonatal warmer.

• A 30-degree hip wedge should be available for left uterine displacement (LUD).

• Obstetricians may want to dose perioperative glucocorticoids for infant lung maturity (requires 48 hours for full effect).

PREOPERATIVE

• Perform evaluation, consent, and discuss plan with obstetrician and surgery team.

• Administer sodium citrate 30 mL orally <30 minutes before induction, if >12 to 16 weeks of gestational age.

  • May consider metoclopramide 10 mg and/or ranitidine 30 mg IV, >30 minutes prior to induction.

• Midazolam is not contraindicated; utilize it if necessary.

INTRAOPERATIVE

• Goal is to maintain appropriate pregnancy homeostasis.

• Pregnancy has been shown to be associated with increased sensitivity to sedatives, anesthetics, opioids, and local anesthetics.

• Maintain normotension.

• If the patient is greater than 20 weeks gestation (uterus at or above the umbilicus), it is crucial to place the patient in LUD prior to induction.

• Recommended initial ventilator settings of 6 to 8 mL/kg of ideal body weight and a respiratory rate of 14 to 18/min.

  • There is a respiratory alkalosis in pregnancy with a normal PaCO₂ of 30 mm Hg. The ventilator setting should be titrated to maintain this PaCO₂ near baseline.

• Volatile anesthetic minimum alveolar concentration (MAC) decreased by 20% to 30% in pregnancy.

• It is essential to ...