Pregnancy

An obstetric patient who presents after trauma or is undergoing a surgical procedure requires special attention. Normal physiologic adaptations to pregnancy include changes in maternal hemodynamic and respiratory parameters. In addition the effects of medications, particularly anesthetic agents, on the fetus must be considered. For elective procedures, the optimal time for surgery is during the second trimester, although surgery can be safely performed at any time throughout the gestation.

It is important to involve an obstetrician in the management of these patients. According to a 2003 American College of Obstetricians and Gynecologists Committee Opinion, “Although there are no data to support specific recommendations regarding nonobstetric surgery and anesthesia in pregnancy, it is important for nonobstetric physicians to obtain obstetric consultation before performing nonobstetric surgery. The decision to use fetal monitoring should be individualized, and each case warrants a team approach for optimal safety of the woman and her baby.”

Care of a pregnant woman requires additional consideration because there is a second patient, the unborn fetus. However, in cases of trauma or musculoskeletal emergency, initial efforts should be focused on the resuscitation and stabilization of the mother. Stabilization of airway, breathing, and circulation is the primary concern. In this regard, the evaluation of the pregnant patient should be the same as the evaluation of a nongravid woman. Significant maternal injuries may easily be overlooked if the focus of attention becomes the fetus. In addition, maintenance of appropriate maternal hemodynamic parameters is crucial for adequate fetal oxygenation in utero. Increasing the partial pressure of oxygen in the maternal blood also increases fetal oxygenation.

Assessment

As the patient is being stabilized, part of the assessment should be determination of the fetal gestational age and well-being; this can be accomplished fairly rapidly with the use of bedside ultrasound. Quick measurements of fetal anatomic parameters such as the cranial biparietal diameter and length of the fetal femur can be obtained to determine the approximate gestational age of the fetus. In addition, ultrasound can visualize fetal cardiac activity, including the force and rate of the heartbeat.

If possible, attempts should be made to displace the uterus off the great vessels. Compression of the aorta and vena cava by the uterus decreases both venous return and cardiac output, which may worsen the maternal condition. The patient may be placed in a lateral position, or, if this is impossible, placement of a wedge under the patient’s hip would be beneficial.

In pregnant patients, as in other patients, time is critical. Survival of both the mother and the fetus is more likely when shock is quickly recognized, support measures are begun, and bleeding is arrested promptly.

Diagnostic testing should proceed as it would for any trauma patient. Imaging studies do not expose the fetus to levels that would cause any adverse effects. Radiation exposure from an abdominal and pelvic CT scan falls below the level associated with causing any fetal anomalies or loss of the pregnancy. In addition, magnetic resonance imaging (MRI) does not produce any ionizing radiation, and there are no reports of any adverse effects to the fetus exposed in utero.

Physiologic Changes in Pregnancy

Multiple normal physiologic changes occur in pregnancy that may affect both the assessment and the management of injuries. Physiologic changes affect virtually every organ system either directly or indirectly. All of the physiologic changes result in an increase in the blood flow to the uterus and fetus. The basic approach to the ABCs of initial resuscitation efforts may be altered during gestation.

In the respiratory system, hyperventilation occurs with increased minute ventilation owing to an increased tidal volume. The total lung capacity decreases about 5%.

The cardiovascular system undergoes multiple changes in the gravid patient. Blood pressure normally decreases during midpregnancy and increases back to prepregnant levels in the third trimester (after 27 weeks’ gestation). This decrease is due to the effect of progesterone on smooth muscle. There is a marked increase in cardiac output, which begins in early gestation. Venous return is a key parameter in this high-output system, and return from the lower extremities may be impeded in later stages of pregnancy by the enlarged uterus. This situation is exacerbated if the patient is in the supine position, a position commonly used in the assessment of an injured patient. If possible, examination of the patient is best done in the left lateral position. If this positioning is impossible, a wedge should be placed under the patient to cause a lateral shift to displace the uterus.

Another physiologic change in the pregnant patient is an increased heart rate. This increase in pulse must be kept in mind when hemodynamic assessment is done, particularly in cases of potential hemorrhage. Plasma volume also increases in pregnancy and peaks around 34 weeks of gestation. This increase is 40% to 50% above nonpregnant levels and ensures uteroplacental perfusion. Although red blood cell mass also increases in pregnancy, it does not increase to the same degree as plasma volume, so there is a normal anemic state during pregnancy ( Table 7-1 ).

TABLE 7-1

Normal Physiologic Changes in the Cardiovascular System During Pregnancy

From Clark SL, Cotton DB, Lee W, et al: Central hemodynamic assessment of normal term pregnancy. Am J Obstet Gynecol 161(6 Pt 1):1439–1442, 1989.

Hemodynamic Measure	12 Weeks Postpartum	36-38 Weeks Gestation	Change from Nonpregnant State
CO	4.3	6.2	+43%
HR	71	83	+17%
SVR	1530	1210	−21%
PVR	119	78	−34%
Oncotic pressure	20	18	−14%
MAP	86	90	NS
PCWP	6.3	7.5	NS
CVP	3.7	3.6	NS

CO, Cardiac output; CVP, central venous pressure; HR, heart rate, MAP, mean arterial pressure; NS, not significant; PCWP, pulmonary capillary wedge pressure; PVR, pulmonary vascular resistance; SVR, systemic vascular resistance.

Fibrinogen levels are normally increased significantly in pregnancy, so that low or low-normal levels should be a cause for concern in the gravid patient. The changes in the coagulation factors result in a normal hypercoagulable state in pregnancy.

In cases of trauma, the increase in plasma volume may mask significant blood loss because the changes in pulse and blood pressures that normally occur early are delayed owing to the increased volume. Orthostatic changes and tachycardia do not typically occur until there is a loss of about 25% of the maternal blood volume. Vital signs may be normal when significant blood loss has occurred. However, the fetus may be experiencing hypoperfusion long before the mother manifests any signs. Larger volumes of fluid replacement also are necessary.

Fluid replacement in these cases is often one of the first priorities. First-line therapy is crystalloid—either normal saline or lactated Ringer solution. Which specific fluid is used is not as important as replacement of adequate volume. Early and rapid fluid resuscitation should be administered even in a normotensive pregnant patient. Transfusion of blood may be crucial because this is one of the most effective ways to improve oxygen capacity and delivery to organs including the gravid uterus.

Diagnostic Imaging in Pregnancy

Many imaging modalities are currently available for diagnosing various musculoskeletal injuries in pregnant women. Of these, x-ray procedures cause the most anxiety among patients and care providers because of the widespread belief that radiation exposure from a limited x-ray is enough to cause harm, or even death, to a growing fetus. In reality, most imaging studies are associated with little or no risk for fetal harm. The accepted cumulative radiation dose in pregnancy is 5 rad. According to the American College of Radiology, there is “no single diagnostic procedure which results in a radiation dose that threatens the well-being of the developing embryo and fetus.” This section reviews the radiation exposure for various imaging studies, potential risks, and methods of minimizing risk in cases in which imaging is needed in pregnancy.

X-ray

Ionizing radiation is composed of high-energy photons that are capable of cell death, teratogenicity, carcinogenesis, and mutations in germ cells. Data on the severity or long-term adverse genetic effects are sparse. Animal studies suggest that high-dose radiation (far greater than the dose used in diagnostic studies) occurring before implantation is likely to result in early embryonic death. Many teratogenic effects have been described in animals with large doses of radiation (100 to 200 rad). Large doses of radiation in pregnant humans have reportedly resulted in abnormalities including fetal growth restriction, microcephaly, and developmental delay. The fetus is most susceptible to the teratogenic effects of ionized radiation, such as ionizing radiation secondary to computed tomography (CT), between weeks 2 and 20 of embryonic life. These effects include, but are not limited to, the microcephaly, microphthalmia, mental delay, growth restriction, cataracts, and behavioral abnormalities.

Perhaps the best human data to suggest the risk of high-dosage radiation exposure comes from atomic bomb survivors, whose fetuses carried a higher risk for central nervous system effects if exposed between 8 and 15 weeks of gestation. Mental delay in fetuses exposed to at least 20 rad was 40%, and for fetuses exposed to 150 rad, it was closer to 60%. Given that there is no increased risk for anomalies, growth restriction, or spontaneous abortion at an exposure less than 5 rad, the risk for any diagnostic procedure is not increased.

The risk of carcinogenesis is also a concern for many patients undergoing radiologic procedures and the providers performing these tests. The actual risk for the development of cancer as a result of in utero exposure to radiation is unknown. Some data suggest that a fetal exposure of 1 to 2 rad may increase the risk of leukemia by a factor of 1.5 to 2.0, increasing the leukemia rate from 1 in 3000 to 1 in 2000.

Abdominal shielding should be used whenever the x-ray procedure allows. The estimated fetal exposure from common radiologic studies is listed in Table 7-1 .

Computed Tomography

The radiation dose to the fetus from a typical CT scan is likely between 1 and 4 rad depending on the study and the gestational age. Although this radiation dose is considerably higher than the radiation dose of a plain x-ray study, it is still below the accepted threshold level for induction of congenital abnormalities. The risk of carcinogenesis is similar to the risk of an x-ray (at a dose of 5 rad, the relative risk of childhood leukemia is 2.0). There is a risk of failed implantation within the first 2 weeks of embryonic life when the dose is greater than 10 rad. At this gestational age (often before the patient is even aware of the pregnancy), there is an “all or none” effect so that should the embryo survive, there are not likely to be any untoward effects.

Magnetic Resonance Imaging

MRI uses magnets that alter the energy state of hydrogen protons rather than using ionizing radiation. Although a relatively new technique for diagnostic imaging in pregnancy, MRI is thought to be a safer alternative to nuclear imaging. MRI is often used to help diagnose fetal abnormalities. Studies of children up to 9 years of age who were exposed to MRI in utero at 1.5 Tesla did not show negative outcomes. Although a small amount of animal data suggest a potential teratogenic effect of MRI in early pregnancy, no such human studies have been published. According to the American College of Radiology, MRI is recommended in pregnancy if the “risk-benefit ratio to the patient warrants that the study be performed.” Results of studies evaluating potential acoustic damage to the fetus from MRI have also shown safety in this area.

Use of the intravenous contrast agent gadolinium in conjunction with MRI has been controversial. Gadolinium crosses the placenta and is excreted by the fetal kidneys into the amniotic fluid. Animal studies of high and repeated doses of gadolinium have been shown to be teratogenic. Although considered a pregnancy category C drug by the U.S. Food and Drug Administration, gadolinium is reserved for cases in pregnancy where the benefits outweigh the potential risks to the fetus.

Nuclear Imaging

Nuclear studies are performed by combining a chemical agent with a radioisotope. These radiopharmaceuticals, when administered intravenously or orally to the patient, can localize to specific organs or cellular receptors, resulting in the ability to image the extent of a disease process in the body. In some diseases, nuclear medicine studies can identify medical problems at an earlier stage than other diagnostic tests. One of the most commonly used isotopes is technetium 99 m (Tc 99 m). The fetal exposure for common nuclear scans such as brain, bone, renal, and cardiovascular scans is small (<0.5 rad).

The American College of Obstetrics and Gynecology published the following guidelines for x-ray examination during pregnancy ( Table 7-2 ):

1

The exposure from a single x-ray procedure does not result in harmful fetal effects. Exposure to less than 5 rad has shown no increase in the rate of fetal anomalies or spontaneous abortion. Patients should be counseled accordingly.
2

The concern regarding fetal effects of high-dose ionizing radiation should not delay or prevent medically indicated diagnostic x-ray procedures from being performed on pregnant women. Imaging procedures such as ultrasound and MRI that are not associated with ionizing radiation should be used in pregnancy in place of x-ray procedures when possible.
3

Radiopaque and paramagnetic contrast agents are unlikely to cause fetal harm; however, they should be used only when medically necessary when the potential benefit outweighs the risk.
4

If multiple x-rays are needed in a pregnant patient, it may be helpful to consult with an expert in radiation dosimetry to calculate a total fetal exposure.
5

MRI and ultrasound are not associated with any harmful fetal effects.