Surgery in the Pregnant Patient

Chapter 72 Surgery in the Pregnant Patient




The pregnant patient presents a unique clinical challenge. An estimated 1% to 2% of pregnant women require surgical procedures, with nonobstetric surgery necessary in up to 1% of pregnancies in the United States each year. In a review of 44 papers and 12,452 patients, the effects of nonobstetric surgical procedures on maternal and fetal outcomes were studied; a maternal death rate of 0.006% and a miscarriage rate of 5.8% were reported. Most indications for surgical intervention are common for the patient’s age group and unrelated to pregnancy, such as acute appendicitis, symptomatic cholelithiasis, breast masses, or trauma. Changes in maternal anatomy and physiology and safety of the fetus are among the issues of which the surgeon must be cognizant. The presentation of surgical diseases in the pregnant patient may be atypical or may mimic signs and symptoms associated with a normal pregnancy, and a standard evaluation may be unreliable because of pregnancy-associated changes in diagnostic tests or laboratory test results. Finally, many physicians may be more conservative in regard to diagnostic evaluation and treatment. Any of these factors may result in a delay in diagnosis and treatment, adversely affecting maternal and fetal outcome. Although consultation with an obstetrician is ideal when caring for a pregnant patient, the surgeon needs to be aware of certain fundamental principles when this resource is unavailable. This chapter discusses key points when caring for the pregnant patient who presents with nonobstetric surgical disorders.



Physiologic Changes Of Pregnancy


Progesterone and estrogen, two of the principal hormones of pregnancy, mediate many of the maternal physiologic changes in pregnancy. Normal laboratory values differ in the gravid compared with the nonpregnant patient. The diaphragm can be elevated in pregnancy up to 4 cm and the lower chest wall can widen up to 7 cm.1 These changes may also mimic similar pathophysiology that occurs in nonpregnant women who have cardiac or liver disease. Elevated progesterone levels, as well as decreased serum motilin, result in smooth muscle relaxation, producing multiple effects on several organ systems. In the stomach, this decreased smooth muscle tone results in diminished gastric tone and motility. The lower esophageal sphincter tone is also decreased and, when combined with increased intra-abdominal pressure, results in an increase in the incidence of gastroesophageal reflux. Small bowel motility is reduced, increasing small bowel transit time. Absorption of nutrients, however, remains unchanged, with the exception of iron absorption, which is increased because of increased iron requirements. In the colon, pregnancy-related changes usually manifest as constipation. This is caused by a combination of increased colonic sodium and water absorption, decreased motility, and mechanical obstruction by the gravid uterus. An increase in portal venous pressure, and therefore an increase in the pressure in the collateral venous circulation, results in dilation of the veins at the gastroesophageal junction. This is of importance only if the patient had esophageal varices before becoming pregnant. The most common result of the increased portal venous pressure is dilation of the hemorrhoidal veins, leading to the well-known complaint of hemorrhoids.


In addition to alterations in smooth muscle tone and motility, other notable changes occur in the gastrointestinal tract. The function of the gallbladder is altered, as is the chemical composition of bile. During the second and third trimesters, the volume of the gallbladder may be twice that found in the nonpregnant state, and gallbladder emptying is markedly slower. Up to 4% of pregnant patients have gallstones on routine obstetric ultrasound.2 Still, only 1 of every 1000 pregnant patients develops symptoms. It is unknown whether the increased biliary stasis, changes in bile composition, or combination of these two factors results in an increased risk for gallstone formation, but the risk for developing gallstones increases with multiparity. However, the incidence of symptomatic cholelithiasis during pregnancy is similar to the incidence in age-related nonpregnant women.


Some of the changes of pregnancy closely resemble those of liver disease. These include spider angiomas and palmar erythema from elevated serum estrogen levels. Hypoalbuminemia is also seen, along with elevated serum cholesterol, alkaline phosphatase, and fibrinogen levels. Serum bilirubin and hepatic transaminase levels remain unchanged during pregnancy.


In the cardiovascular system, peripheral vascular resistance is decreased as a consequence of diminished vascular smooth muscle tone. Cardiac output increases by as much as 50% during the first trimester of pregnancy. Initially, this is caused by an increased stroke volume resulting from an increase in plasma volume and red blood cell mass, but a gradual increase in maternal heart rate also is a contributing factor. Cardiac output falls back to almost normal late in pregnancy, usually during the 36th to 40th weeks of gestation. During the third trimester, cardiac output is dramatically decreased when the mother is lying supine. This is caused by compromised venous return from the lower extremity caused by compression of the inferior vena cava by the gravid uterus. In the supine position, the inferior vena cava may be completely occluded; venous drainage of the lower extremities is through collateral channels. With this drop in preload, an increase in sympathetic tone usually maintains peripheral vascular resistance and blood pressure. However, up to 10% of patients may experience supine hypotensive syndrome, in which the sympathetic response is not adequate to maintain blood pressure. During anesthesia induction in the operating room, anesthetic agents may inhibit the compensatory sympathetic response, causing a more precipitous fall in blood pressure. From a surgeon’s perspective, it may be necessary to place the patient in the left lateral decubitus position during procedures performed during the third trimester, relieving caval compression by the enlarged uterus.


Inguinal swelling secondary to varicosities of the round ligament is also a phenomenon that occurs during pregnancy. The increase in swelling is a result of hormonal and mechanical changes. It is often mistaken for an inguinal or femoral hernia. Appropriate treatment includes careful physical examination and ultrasound if needed. The varicosities generally resolve postpartum.


Oxygen consumption increases during pregnancy. Minute ventilation increases by 50% because of an increase in tidal volume, which appears to be a result of an elevated serum progesterone level.1 Progesterone not only increases the sensitivity of the respiratory centers to CO2 but also acts as a direct stimulant to the respiratory centers. As a consequence of the increased minute ventilation, the maternal PaO2 level during late pregnancy ranges from 104 to 108 mm Hg and the maternal PaCO2 level ranges from 27 to 32 mm Hg. Renal compensation maintains a normal maternal pH. The decreased PaCO2 level increases the CO2 gradient from the fetus to the mother, facilitating CO2 transfer from the fetus to the mother. The oxygen-hemoglobin dissociation curve of maternal blood is shifted to the right; this, coupled with the increased affinity of fetal hemoglobin for oxygen, results in increased oxygen transfer to the fetus. Elevation of the diaphragm by as much as 4 cm results in a decrease in total lung volume by 5%. Diminished expiratory reserve volume and residual volume result in a functional residual capacity that is 20% lower than that in the nonpregnant woman. Vital capacity and inspiratory reserve volume remain stable.


In the kidney, there is an increase in the glomerular filtration rate by 50% that accompanies a 75% increase in renal plasma flow. Urinary glucose excretion increases as a direct consequence of the increased glomerular filtration rate. The blood urea nitrogen level decreases by 25% during the first trimester and is maintained at that level for the remainder of the pregnancy. The serum creatinine level also decreases by the end of the first trimester from a nonpregnant value of 0.8 to 0.7 mg/dL and may be as low as 0.5 mg/dL by term. A five- to tenfold increase in the serum renin level occurs, with a subsequent four- to fivefold increase in the angiotensin level. Although the pregnant patient is apparently less sensitive to the hypertensive effects of the increased angiotensin, elevated aldosterone levels result in an increase in sodium reabsorption, overcoming the natriuresis produced by elevated progesterone levels. Serum sodium levels are decreased, however, because the increase in sodium reabsorption is less than the increase in plasma volume. Serum osmolality is decreased to 270 to 280 mOsm/kg.1


The increase in plasma volume and red blood cell mass is accompanied by a progressive rise in the leukocyte count during pregnancy. During the first trimester, the white blood cell count ranges from 3,000 to 15,000 cells/mm3, increasing to a range of 6,000 to 16,000 cells/mm3 during the second and third trimesters.1 The platelet count progressively declines throughout pregnancy, whereas the mean platelet volume tends to increase after 28 weeks’ gestation. As noted, fibrinogen levels are elevated to a range of 400 to 500 mg/dL. Plasma levels of factors VII, VIII, IX, and X also rise progressively, whereas levels of factors XI and XIII decline, and levels of factors II, V, and XII remain unchanged. Despite these alterations in the coagulation cascade and platelet count, bleeding and clotting times are unchanged.



Safety Concerns In Pregnancy



Radiologic Concerns


Radiographic studies remain useful diagnostic tools for the pregnant patient. Of greatest concern with radiation exposure is the risk to the fetus from the exposure. The accepted maximum dose of ionizing radiation during the entire pregnancy is 5 cGy. The fetus is at the highest risk from radiation exposure from the preimplantation period to approximately 15 weeks’ gestation. Primary organogenesis occurs during this time and the teratogenic effects of radiation, particularly to the developing central nervous system, are at their highest. Perinatal radiation exposure has also been associated with childhood leukemia and certain childhood malignancies. The radiation dose that has been associated with congenital malformation is higher than 10 cGy. As shown in Table 72-1, radiation exposure to the fetus with the doses from the more common radiology procedures is well below that threshold. Nonetheless, prudence on the part of the clinician is required to avoid unnecessary fetal exposure to ionizing radiation, especially during the first and early second trimesters, when the risk from exposure is greatest.


Table 72-1 Fetal Radiation Exposure With Radiographic Imaging






























EXAMINATION TYPE ESTIMATED FETAL RADIATION EXPOSURE (cGy)
Two-view chest radiography 0.00007
Cervical spine radiography 0.002
Pelvis radiography 0.04
Head CT <0.050
Abdomen CT 2.60
Upper GI series 0.056
Barium enema 3.986
Hepatobiliary (HIDA) scanning 0.150

GI, Gastrointestinal; HIDA, hepatobiliary iminodiacetic acid.


Magnetic resonance imaging (MRI) avoids exposure to ionizing radiation but poses an unknown risk to the fetus. Animal studies have shown no teratogenic effect or increased incidence of fetal death or congenital malformations from the electromagnetic radiation, static magnetic field, radiofrequency magnetic fields, or IV contrast agents used during MRI. Theoretically, the gradient magnetic fields may produce electric currents in the patient and the high-frequency currents induced by radiofrequency fields may cause local generation of heat. The long-term effect of exposure is not known.3 The National Radiological Protection Board has advised against the use of MRI during the first trimester of pregnancy.


Contrast media may be administered with various techniques of body imaging. If computed tomography (CT) has been performed during pregnancy with iodide contrast, neonatal thyroid function should be checked during the first week after delivery. No effect on the fetus has been observed after the use of gadolinium contrast medium with MRI.


Ultrasonography is routinely used by obstetricians during pregnancy. Although tissue heating and cavitation are theoretical effects of ultrasound exposure, such effects have never been reported. Ultrasound may be a helpful alternative diagnostic tool when trying to avoid exposure to ionizing radiation, but does have some limitations. Deeper structures are difficult to visualize and may be obscured by superficial structures that are more echodense. Ultrasound imaging has a limited field of view and is highly operator-dependent. Despite these limitations, certain disease processes, such as a palpable breast mass or suspected appendicitis, may be evaluated effectively and safely.



Medication Concerns


The surgeon will on occasion need to prescribe medications to treat the pregnant patient with surgical disease. In this section, we provide an overview of medications that the surgeon may commonly prescribe. The list is by no means comprehensive and, prior to using any medication, consultation with the patient’s obstetrician is necessary.


The U.S. Food and Drug Administration (FDA) ranks the following as the least harmful classes of drugs during pregnancy:




The FDA offers the following classifications for prescription drugs that should not be taken during pregnancy:






Analgesics





Antibiotics


Antibiotics may be necessary to treat various surgery-related illnesses in pregnancy. These are listed by class.














Anesthesia Concerns


Anesthesia concerns during pregnancy include the safety of the mother and fetus. The fetus may be affected by exposure to teratogenic effects of anesthetic agents, risk for preterm labor, and risk from changes in maternal physiology as a consequence of anesthesia. Changes in uterine blood flow and maternal acid-base status may cause hypoxemia or asphyxia in the fetus. These can be a result of maternal hypotension or hypoxia, maternal hyperventilation, or placental passage of anesthetic agents that affect the fetal central nervous or cardiovascular system.


The effects of anesthesia during pregnancy can be divided into direct, or active, and indirect, or passive, effects. The direct effects relate to the possible teratogenic or embryotoxic properties of the drugs used for anesthesia, some of which cross the placenta. The indirect effects are those mechanisms whereby an anesthetic agent or surgical procedure may interfere with maternal or fetal physiology and, in doing so, harm the fetus. For the most part, the fetus experiences indirect effects as a consequence of anesthetic agents administered to the mother and hemodynamic changes in the mother from blood loss or anesthetic agents. The most profound effects on the fetus are related to decreased uterine blood flow or decreased oxygen content of uterine blood. Unlike circulation to other vital organs, most notably the brain, the uterine circulation is not autoregulated. During the third trimester, uterine circulation represents almost 10% of cardiac output. When treating maternal hypotension, vasopressors such as dopamine and epinephrine, although increasing the maternal systemic pressure, have little or no effect on uterine circulation. Phenylephrine and metaraminol are alpha agonists that are effective in maintaining maternal blood pressure and preventing fetal acidosis.5 Other maneuvers, such as fluid bolus, Trendelenburg position, compression stockings, and leg elevation, have a larger impact on increasing uterine blood flow.


In addition to the risks related to maternal hypoxia or hypotension, the risk for spontaneous abortion and teratogenesis related to anesthetic agents is of major concern. Many nonhuman studies have demonstrated different teratogenic effects with similar agents but have not led to definitive conclusions regarding their teratogenic potential in humans. For a congenital defect to result, exposure to the teratogen must occur during the vulnerable differentiation stage of the affected organ system. As noted, differentiation of the major organ systems occurs during the first trimester of human embryonic development. Therefore, delaying semielective surgical procedures until after the first trimester may reduce the risk for teratogenicity. However, large survey studies have demonstrated an increased risk for spontaneous abortions, intrauterine growth retardation, and low-birth-weight neonates in women who require surgery during pregnancy. These studies lacked information on the indications for nonobstetric surgical procedures.


Elective surgical procedures are delayed until at least 6 weeks after delivery, when maternal physiology has returned to the nonpregnant state and when the impact on the fetus is no longer a concern. When emergent procedures are required, obviously the life of the mother takes priority, although an experienced anesthesiologist will be able to modify the anesthesia used according to maternal physiology and fetal well-being. For semielective surgical procedures, attempts are made to delay surgery until after the first trimester, whenever possible. This needs to be determined on an individual basis because continued exposure to the underlying disease process may be more harmful than the operative risk to the mother and fetus. During the second trimester, after organ system differentiation has occurred, there is almost no risk for anesthetic-induced malformation or spontaneous abortion. Later in pregnancy, during the third trimester, the risk for preterm delivery is at its highest.


When the pregnant patient requires surgical intervention, consultation with the obstetrician and possibly a perinatologist is essential. The specialist is helpful in determining the optimum technique to monitor fetal status and can assist with perioperative management and diagnose and manage preterm labor. Typically, when emergent surgery occurs during the first or early second trimester, fetal heart tones are monitored before and after anesthesia exposure. During the late second and third trimesters, when the fetus is of viable age, continuous intraoperative monitoring is performed when possible. Transvaginal ultrasound can be used when the surgical field involves the abdomen. Continuous monitoring is used if significant blood loss is possible or anticipated to assess fetal well-being. Checking the fetal heart rate for fetal status and tocometer monitoring for uterine activity are done before and after the procedure, even if intraoperative monitoring is not believed necessary or is unavailable.


Postoperative pain control in the pregnant patient needs to be monitored closely. NSAIDs are not used in pregnancy because of the risk for premature closure of the ductus arteriosis.6 Morphine and fentanyl are both good IV choices postoperatively. Morphine has a higher associated incidence of nausea and vomiting, but most surgeons have extensive experience with it. A patient-controlled analgesia pump after surgery may be the best choice because of the associated low incidence of maternal respiratory depression and drug transfer to the fetus.


Postoperative oral narcotic use is generally considered safe in pregnancy. Narcotic analgesics have not been found to cause birth defects in humans in normal dosages. Oxycodone, hydrocodone, and codeine are commonly used narcotics and can be safely used in moderation. Chronic use of narcotics during pregnancy may cause fetal dependency. It is recommended that the pregnant postsurgical patient be weaned off narcotic use as soon as possible.



Prevention Of Preterm Labor


The incidence of preterm labor associated with nonobstetric surgery is related to gestational age and the indication for surgery. Studies have suggested that the rate of premature labor induced by nonobstetric surgical intervention is 3.5%. Gestational age at treatment and severity of the underlying disease are the most predictive indicators of patients at risk for preterm labor. The later in gestation is the patient, the higher the risk for preterm contractions or preterm labor. Intraperitoneal surgeries and disease processes with intraperitoneal inflammation are the most likely to have a postoperative course complicated by preterm contractions and preterm labor. In a number of studies, a significant difference was found in the number of patients with preterm contractions based on the average time from onset of symptoms to operative intervention. A delay in treatment appears to increase the chance of preterm labor, likely related to the primary disease process. Laparoscopic and open techniques have an equal associated incidence of preterm labor.


There is no general consensus on the use of prophylactic tocolytics after nonobstetric surgery during pregnancy. Tocolytic use varies widely among centers and physicians. Most studies have suggested that tocolytics only be used if contractions are noted during postoperative monitoring or are appreciated by the patient. Tocolytics used as needed are generally successful at preventing preterm labor and preterm delivery when postoperative contractions are detected. Terbutaline, magnesium, and indomethacin (Indocin) have been used in different studies, with equivalent results. Almost 100% of patients with postoperative contractions were successfully given tocolytics and delivered at term. In general, for patients with postoperative contractions before 32 weeks, indomethacin would be a reasonable treatment, whereas terbutaline could be used as first-line treatment for patients at more than 32 weeks’ gestation. The use of prophylactic tocolysis is individualized, depending on the patient’s gestational age and underlying disease process.



Abdominal Pain And The Acute Abdomen In Pregnancy


When the pregnant patient presents with abdominal pain, it may be difficult to distinguish a pathophysiologic cause from normal pregnancy-associated symptoms. Changes in the position and orientation of abdominal viscera from the enlarging uterus, and the alterations in physiology already described, may modify the perception or manifestation of an intra-abdominal process. If it is early in the pregnancy, the woman may not know that she is pregnant. Also, some intra-abdominal processes are exclusive to pregnancy, such as ectopic pregnancy, HELLP (hemolysis, elevated liver enzymes, low platelets) syndrome, or acute fatty liver of pregnancy. Both patient and physician may attribute the patient’s complaints to normal pregnancy, resulting in a delay in evaluation and treatment. These delays in diagnosis and definitive intervention are the most serious adverse events affecting maternal and fetal outcome. It is usually not the treatment but the delay in diagnosis and severity of the primary disease process that affects outcomes poorly. Box 72-1 lists the more common causes of abdominal pain in the pregnant patient, classified according to location.


Aug 1, 2016 | Posted by in CARDIAC SURGERY | Comments Off on Surgery in the Pregnant Patient

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