Physiologic Changes in Pregnancy and Implications for Perioperative Nonobstetric Surgery

By Moises Auron, MD, FAAP, FACP, SFHM, Marina Y Duran Castillo, MD, FACP and Omar Felipe Duenas Garcia, MD, MPH, FACOG

*Please note: This is an excerpt from an article first published in the Cleveland Clinic Journal of Medicine. To view the article in its entirety, along with a complete list of references, please visit: https://www.ccjm.org/content/88/1/27.

Nonobstetric surgery during pregnancy should be avoided if possible, but when surgery is required, an obstetrician should be part of the perioperative team. In general, preoperative assessment is similar regardless of whether a woman is pregnant, but cardiovascular, pulmonary, hematologic and renal changes of pregnancy can increase surgical risk and must be taken into account. Special management considerations include pregnancy-associated laboratory changes, timing of surgery, anesthesia choice, intubation precautions, patient positioning, preoperative blood typing, intraoperative fetal monitoring and venous thromboembolism prophylaxis.

Important physiologic changes take place during pregnancy that optimize maternal and fetal outcomes but increase risk during surgery. Accommodating normal changes and identifying and managing risk factors should guide perioperative planning.

Nonobstetric surgery in pregnancy is rare and risky

From 0.2% to 2.0% of pregnant women undergo nonobstetric surgery.1,2 In order of frequency, the most common procedures are appendectomy, cholecystectomy, adnexal surgery (for torsion or masses), trauma repair, small-bowel obstruction surgery and breast surgery.2–4

The American College of Surgeons National Surgical Quality Improvement Program reported a postoperative complication rate of 5.8% in pregnancy. Complications included reoperation within 30 days (3.6%), infections (2%), wound problems (1.4%), respiratory complications (2%), thromboembolic complications (0.5%), transfusion requirements (0.2%) and death (0.25%).4

A study of 5,591 pregnant women in Taiwan5 found that the rates of the following postoperative complications were higher than among nonpregnant women:

• Sepsis (odds ratio [OR] 1.75, 95% confidence interval [CI] 1.47–2.07)
• Pneumonia (OR 1.47, 95% CI 1.01–2.13)
• Urinary tract infection (OR 1.29, 95% CI 1.08–1.54)
• Death (OR 3.94, 95% CI 2.62–5.92).

One of the most common and feared complications from the obstetric perspective is preterm delivery. In a series of 86 pregnant women who underwent nonobstetric surgery in 1992 through 2014, the rate was 41% despite low rates of intraoperative and immediate postoperative complications.6

General perioperative considerations

• Timing of surgery. Elective surgery should be postponed until after delivery, but urgent procedures necessary to save a patient’s life should be pursued regardless of pregnancy stage.45 Although patients can be reassured that anesthetic gases do not appear to be teratogenic, surgery during the first trimester may affect the rest of the pregnancy.23 The third trimester poses the highest risk for both mother and fetus; at that time, surgery becomes more technically difficult, and the fetus’s higher perfusion needs increase the risk of fetal hypoxia. If there is a choice, the second trimester is the best time to undergo necessary surgery.
• Include an obstetrician on the team. The American College of Obstetricians and Gynecologists and the American Society of Anesthesiologists recommend involving an obstetric specialist to help assess and manage pregnant women requiring any surgical or invasive procedure. An obstetric care provider with cesarean delivery privileges and a pediatric or neonatologist team should be available during the procedure.
• Minimally invasive is best. Particularly for patients needing abdominal surgery, a laparoscopic approach is preferred to reduce risk of fetal complications.46,47
• Avoid supine positioning. During the second and third trimesters of pregnancy, the uterus compresses the inferior vena cava when the patient lies flat, reducing venous return by about 30%, with a consequent decrease in cardiac output and placental perfusion. For these reasons, patients should lie on their side during surgery.48In a study using magnetic resonance imaging,49 the maximum aortocaval decompression was achieved with a left-lateral tilt position of 30°. The anesthesiologist should place the patient in a 30° left lateral decubitus position and maintain normovolemia, oxygen saturation greater than 95%, and normal arterial pressure of carbon dioxide.45,50
• Preoperative diagnostic tests. The most commonly required tests include hematocrit and preoperative blood type and antibody screen. Otherwise, routine preoperative testing is not justified for most patients with no active systemic comorbidity.23,51The need for other studies is based on risk factors and predisposing conditions.2,12,52
• Fetal monitoring. Viable fetuses older than 23 weeks gestational age (or > 22 weeks in some centers) should have continuous monitoring and simultaneous contraction activity monitoring throughout any surgical procedure.

Anesthesia considerations

Identifying risk factors for complications associated with induction of anesthesia is paramount. In addition to a physical assessment, clinicians should ask about personal and family history of bleeding disorders, coagulopathy and complications related to anesthesia (e.g., malignant hyperthermia).23

Risk of anesthetic morbidity and mortality in pregnancy are most associated with airway edema, restrictive lung physiology and aspiration.53 Other risk factors are eclampsia or preeclampsia, postpartum shock, pulmonary embolism, obesity, uncontrolled arterial hypertension and emergency surgery.54, 55

Increasing use of regional anesthesia instead of general anesthesia56 during delivery has led to reduced mortality. Hawkins et al57 found a 59% reduction (from 2.9 to 1.2 deaths per million patients) in anesthesia-related maternal mortality in the years 1991 to 2002 compared with 1979 to 1990. The relative risk of death during general anesthesia decreased from 6.7 before 1996 to 1.7 after that year. The improvements were associated with reduction in general anesthesia, as regional anesthesia rates increased during that time.

• Neuraxial anesthesia preferred. Neuraxial anesthesia is preferred if possible. However, specific changes in the central nervous system affect neuraxial anesthesia during pregnancy. Epidural vein engorgement and reduced epidural-space volume increase the spread of epidurally injected local anesthetics and also the risk of a bloody spinal tap.2 Anticoagulation considerations for neuraxial anesthesia are similar in pregnant and nonpregnant patients. Before performing a neuraxial procedure, it is recommended to wait at least 12 hours (for prophylactic dosages) and 24 hours (for full anticoagulation dosages) after administering the last dose of LMWH, and 6 hours after an unfractionated heparin infusion.31