Trauma in Pregnancy
Penetrating injuries to the gravid uterus date back to antiquity, when wounding instruments included spears, sticks, and animal horns. Ambroise Paré, famous for his skills as a military surgeon, was also an obstetrician and was among the first to describe the treatment of gunshot wounds to the uterus. Paré wrote, “When the womb is wounded, the blood cometh out at the privites, and all other accidents appeared …”1 Maternal deaths resulting directly from pregnancy or the complications of labor and delivery have declined sharply in recent years. In the United States, the absolute risk of pregnancy-related death is estimated currently at 11.8 deaths per 100,000 live births, a reduction in death rate by 99% since 1900.2,3 In contrast, trauma has emerged as the leading cause of death during pregnancy, accounting for nearly 50% of maternal deaths in the United States and over 1 million deaths annually worldwide.3,4 An estimated 6–7% of pregnancies are complicated by trauma with 0.4% of all pregnant patients requiring hospitalization for the treatment of injuries.5 Interestingly, the incidence of trauma increases with each pregnancy trimester, with only 8% of injuries occurring during the first trimester and over 50% during the third trimester.6 The true number of injured gravid women is grossly underestimated by these figures, however, as many injuries are unreported, especially those resulting from domestic violence. Thus, it is essential that all trauma care professionals recognize the anatomic and physiologic changes unique to pregnancy and appreciate how these changes impact the evaluation and treatment of the injured gravid patient. Complete evaluation of these patients includes an assessment of the fetus, and the treating physician must not only be cognizant of the signs of fetal distress, but must also be able to make rapid interventions in the interest of saving both mother and baby.
EPIDEMIOLOGY OF TRAUMA IN PREGNANCY
Weiss et al.7 examined data from the Pennsylvania state trauma registry and found that, among a total of 16,722 women of childbearing age who required hospitalization for injuries over a 1-year period, 761 were pregnant (4.6%). The leading causes of injury among pregnant women in this series were transportation-related (33.6%), falls, and assaults. Younger women (mean age 25) appeared to be at higher risk for injuries when compared to older gravid women. In a recent study from the state of Utah, pregnant women with an injury-related visit to an emergency department (ED) were more likely than noninjured women to experience preterm labor, placental abruption, and cesarean delivery, and infants born to women who were injured were more likely to be born preterm.8 In a related study that included data from 16 states, 240 trauma-related fetal deaths were identified (3.7 fetal deaths per 100,000 live births).9 Motor vehicle crashes were again the leading mechanism resulting in fetal death (82% of cases), followed by firearms (6%) and falls (3%). Placental injury was mentioned in 100 cases, and maternal death was the cause of fetal death in 11% of the cases. Again, pregnant mothers ages 15–19 years appeared to be at greatest risk for trauma-related fetal loss.
Young pregnant women are at significant risk of sustaining injuries as the result of an assault also. Battering can begin or escalate during pregnancy, and it is estimated that between 10 and 30% of women are abused during pregnancy, with fetal death occurring in 5%.10 In a series of 41 injury-related deaths during pregnancy reported from North Carolina, half of the patients were known or suspected of having been abused.11 Physical abuse is suggested by proximal and midline injuries rather than distal injuries, trauma to the neck, breast and face, and injuries to the upper arms and lateral thighs. Cigarette burns and bites should raise the level of suspicion for the examiner also.12 A history of depression, substance abuse, or frequent visits to the ED are other factors that suggest domestic violence. Domestic violence is not dependent on age, race, or marital status and cuts across all socioeconomic classes. Thus, it is imperative that all health care providers recognize the signs and symptoms of physical abuse and the opportunity to intervene and protect both the mother and her fetus (see Chapter 46).
Chang et al.13 recently summarized data from the Pregnancy Mortality Surveillance System at the Centers for Disease Control and Prevention (CDC), focusing on risk factors for pregnancy-associated homicide. According to this report, homicide was the third leading cause of injury-related death for all women of childbearing age, pregnant or not. The pregnancy-associated homicide ratio was 1.7 per 100,000 live births. Risk factors for homicide in this group included age younger than 20 years, black race, and either late or no prenatal care, and firearms were the leading mechanism (56.5%). It is hoped that the new surveillance system developed by the CDC, the National Violent Death Reporting System, which captures information about pregnancy status, victim–perpetrator relationships, and the presence of intimate partner violence, will provide more comprehensive data on this important mechanism of injury among women. Ikossi et al.14 utilized the American College of Surgeons’ National Trauma Data Bank (NTDB) to develop a profile of mothers at risk for injury during pregnancy. Among the 77,321 women of childbearing age who were hospitalized after injury, 1,195 (1.5%) were pregnant. The major mechanism of injury among the pregnant patients was a motor vehicle crash (70%), followed by interpersonal violence (11.6%) and falls (9.3%). Young age, African American or Hispanic ethnicity, and insurance status (none or underinsured) identified women at highest risk for injury during pregnancy, and these groups are most likely to benefit from efforts at primary trauma prevention (see below).
ANATOMIC AND PHYSIOLOGIC CHANGES UNIQUE TO PREGNANCY
Although the initial assessment and management priorities for resuscitation of the injured pregnant patient are the same as those for other traumatized patients (see Chapter 10), the specific anatomic and physiologic changes that occur during pregnancy may alter the response to injury and, hence, necessitate a modified approach to the resuscitation process. Most of these anatomic, physiologic, and biochemical adaptations occur in response to physiologic stimuli provided by the fetus. An understanding of these adaptations (summarized in Table 37-1) is necessary in order to provide appropriate and timely care to both mother and unborn child. Although nearly every system in the body is affected by pregnancy, the most important changes involve the cardiovascular, pulmonary, and reproductive systems.
TABLE 37-1 Summary of Normal Physiologic Changes During Pregnancy
Cardiovascular System
Plasma volume begins to expand at 10 weeks’ gestation and increases by 45% at full-term as compared to pregravid levels.15 This hypervolemic state is protective for the mother, as fewer red blood cells are lost during hemorrhage and, hence, the oxygen-carrying capacity of her blood is less affected.16 Furthermore, the hypervolemia prepares the patient for the blood loss that accompanies a vaginal delivery (500 mL) or cesarean section (1,000 mL). This pregnancy-induced hypervolemia, however, may create a false sense of security for the resuscitating physician because almost 35% of maternal blood volume may be lost before there are signs of hypovolemic shock. This increase in plasma volume is accompanied by an erythroid hyperplasia in the bone marrow, resulting in a 15% increase in red blood cell mass and a “physiologic anemia.” This anemia of pregnancy is greatest at 30–32 weeks’ gestation and will be most significant in patients who have not received iron supplements.16 In addition, factors VII, VIII, IX, X, and XII, and fibrinogen are increased, fibrinolytic activity is reduced, and the net result is a hypercoagulable state, putting the patient at increased risk for thromboembolic events.
During the first trimester, maternal pulse rate increases by about 10–15 beats/min and remains elevated until delivery. As the diaphragm becomes progressively more elevated secondary to the enlarging uterus, the heart is displaced to the left and upward, resulting in a lateral displacement of the cardiac apex. Moreover, each pregnant woman has some degree of a benign pericardial effusion. Both of these changes result in an enlarged cardiac silhouette and increased pulmonary vasculature on the chest x-ray.17 Maternal blood pressure decreases during the first trimester, reaches its lowest level in the second trimester, and then rises toward pre-pregnancy levels during the final 2 months of gestation. The mean blood pressure values are 105/60 mm Hg for the first trimester, 102/55 mm Hg for the second trimester, and 108/67 mm Hg for the third. By the end of the first trimester, cardiac output increases to 25% above normal. In the healthy gravida, this increased workload on the heart is well-tolerated.
When the patient is in the supine position and the inferior vena cava is partially obstructed by the gravid uterus, there is a decrease in blood return to the heart resulting in a lower cardiac output and causing the “supine hypotensive syndrome.” This syndrome is marked by dizziness, pallor, tachycardia, sweating, nausea, and hypotension. Turning the mother onto her left side restores the circulation and increases cardiac output by about 30% after 20 weeks’ gestation. A point worth emphasizing is that in the supine position, the enlarged uterus also compresses the aorta, reducing the pressure in the uterine arteries and decreasing blood flow to the fetus.18 Importantly, the uterine arteries are maximally dilated during pregnancy so that autoregulation is absent and thus blood flow to the fetus is entirely dependent upon maternal mean arterial blood pressure.6
Respiratory System
Several changes in the maternal respiratory system occur during pregnancy to meet increased oxygen requirements. As the uterus enlarges, the diaphragm rises about 4 cm and the diameter of the chest enlarges by 2 cm, increasing the substernal angle by 50%.19 Care should be taken to consider these anatomic changes when thoracic procedures such as tube thoracostomies and thoracenteses are being performed. Functional residual capacity (FRC) decreases because of a decline in expiratory reserve and residual volumes. The net result is an unchanged arterial partial pressure of oxygen (PaO2), a reduction in the partial pressure of carbon dioxide (PCO2) to 30 mm Hg, and a slight compensatory decrease in plasma bicarbonate levels.20 Therefore, pregnancy is a state of partially compensated respiratory alkalosis. Relative to these changes, the injured gravida tolerates apnea poorly because of the reduced FRC. Hence, supplemental oxygen is always indicated for these patients. Due to the weight gain associated with pregnancy, the Mallanpati score increases, making intubation more difficult and increasing the incidence of fatal failed intubation by 13 times.21,22
Reproductive System
By the end of full-term gestation, the weight of the uterus has increased to 20 times its prepregnancy weight (i.e., from 60 to about 1,000 g). After the 12th week of pregnancy, the uterus extends out of the pelvis, rotates slightly to the right, and ascends into the abdominal cavity to displace the intestines laterally and superiorly. At 10 weeks’ gestation, uterine blood flow is estimated to be about 50 mL/min. With progressive uterine enlargement, uterine blood flow increases dramatically to approximately 500 mL/min at term, constituting up to 17% of the cardiac output.23 Uterine veins may dilate up to 60 times their size in the pre-pregnant state, allowing for adequate venous drainage to accommodate the uteroplacental blood flow. This increased vascularity carries an attendant risk of massive blood loss with a pelvic injury.
INITIAL ASSESSMENT AND MANAGEMENT
Prehospital Care
Prehospital care is an extension of the trauma system (see Chapter 4) and must be appropriately adapted to the needs of the injured gravid patient. In particular, the importance of providing an adequate airway and supplemental oxygen to prevent fetal hypoxia must take priority during field transport. Also, it is important to recognize that the relative hypervolemia of pregnancy may mask the usual signs and symptoms of acute blood loss. Thus, intravenous fluids should be given liberally during transport in these patients. A wedge placed under the right hip may help avoid the vena cava compressive syndrome described above. Any information on the length of the gestation and prenatal care and complications that can be obtained should be relayed to the receiving trauma center.
Primary Survey
As with any other injured patient, the primary survey of the injured pregnant patient addresses the airway, breathing, and circulation, with the mother receiving treatment priority (see Chapter 10). Ensuring an adequate maternal airway with supplemental oxygen is essential for preventing maternal and fetal hypoxia (see Chapter 11). Because the oxyhemoglobin dissociation curve for fetal blood is different from that for maternal blood, small increments in maternal oxygen concentration improve the blood oxygen content and reserve for the fetus, even though the maternal arterial oxygen content does not change appreciably. Of note, because pseudocholinesterase levels decrease during pregnancy, lower doses of succinylcholine may be used during rapid sequence intubation.24 As mentioned above, due to the expansion of the intravascular volume, signs of shock in the mother may be delayed until over 35% of blood loss has occurred; however, the fetus will be in jeopardy before this point. Thus, fluid and blood resuscitation should be vigorous. In late pregnancy, it is wise to refrain from the use of femoral catheters for resuscitation. Although the role of ED thoracotomy in pregnancy remains to be defined, it is the opinion of the authors that it should be considered in conjunction with perimortem cesarean section (see below).25
Secondary Survey and Maternal Assessment
Following the primary survey of the patient and performance of life-saving measures, the secondary survey is initiated. This consists of obtaining a thorough history, including an obstetric history. An accurate prenatal history is crucial because comorbid factors such as pregnancy-induced hypertension, diabetes mellitus, and congenital heart disease may alter management decisions. Furthermore, a history of preterm labor, placental abruption, or placenta previa puts the patient at increased risk for the recurrence of these conditions. The obstetric history includes the date of the last menstrual period, expected date of delivery, and date of the first perception of fetal movement, and any problems or complications of the current and previous pregnancies. Whenever possible, the obstetrical team should be immediately notified and respond to the trauma room for patients in their second or third trimester of pregnancy.
During the secondary survey, appropriate x-rays should be ordered as during any trauma evaluation, shielding the uterus whenever possible (see below). The Focused Assessment with Sonography in Trauma (FAST) examination (see Chapter 16) is strongly recommended during the secondary survey to detect pericardial or peritoneal fluid in the mother. Although there is some debate on the sensitivity of ultrasound in this setting, most report an 80% sensitivity and a 100% specificity in detecting fluid using the FAST examination during pregnancy.26 A small amount of free fluid in the pelvis may be normal during pregnancy, but this trace amount (7–21 mL) is too small to be detected during a routine transabdominal ultrasound examanition.27 Therefore, any amount of fluid seen on the FAST examination should be considered pathologic even during pregnancy.
As part of the abdominal examination, determination of the uterine size provides an approximation of gestational age and fetal maturity. Measurement of fundal height is a rapid method for estimating fetal age. If, for example, the most superior part of the fundus is palpated at the umbilicus, the fetal age is estimated to be 20 weeks. A discrepancy between dates and uterine size may result from a ruptured uterus or intrauterine hemorrhage. Determination of fetal age and fetal maturity is an important factor in the decision matrix regarding early delivery. In general, a 25-week-old fetus is considered viable if given neonatal intensive care. Fig. 37-1 contains a helpful algorithm summarizing the initial evaluation of the injured pregnant patient.
FIGURE 37-1 Algorithm for the initial evaluation and resuscitation of the injured mother and fetus.
Evaluation of the Fetal–Placental Unit
Evaluation of the state of the pregnancy focuses on the following: (a) vaginal bleeding; (b) ruptured membranes (amniotic sac); (c) a bulging perineum; (d) the presence of contractions; and (e) an abnormal fetal heart rate (FHR) and rhythm. These five conditions indicate the acute status of the pregnancy. Vaginal bleeding prior to labor is abnormal and may indicate premature cervical dilation, early labor, placental abruption (separation of the placenta from the uterine wall), or placenta previa (location of the placenta over a portion of the cervical os). A ruptured amniotic sac should be suspected when cloudy white or green fluid is observed coming from the cervical os or perineum. The presence of amniotic fluid can be confirmed by the change in color of nitrazine paper from blue–green to deep blue when the fluid is tested. Rupture of the amniotic sac is significant because of the potential for infection and prolapse of the umbilical cord, the latter being an obstetric emergency requiring immediate cesarean section. Bloody amniotic fluid is an indication of premature separation of the placenta (placental abruption) or placenta previa. In the presence of known or continuous meconium staining (green amniotic fluid), continuous electronic fetal monitoring is necessary. A bulging perineum is caused by pressure from a presenting part of the fetus. If this occurs during the first trimester, spontaneous abortion may be imminent.
Assessment of the pattern of uterine contraction is accomplished by resting the hand on the fundus and determining the frequency, duration, and intensity of contractions. Contractions are usually rated as mild, moderate, or strong. Strong contractions are associated with true labor, and assessment for their presence is important so that appropriate preparation can be made for delivery and resuscitation of the neonate if necessary.
The Kleihauer–Betke (KB) test is used after maternal injury to identify fetal blood in the maternal circulation (i.e., fetomaternal transfusion). Adult hemoglobin (HbA) is eluted in the presence of an acidic buffer, whereas fetal hemoglobin (HbF) is resistant to elution. Fetal cells containing HbF are stained with erythrosine, whereas maternal cells containing HbA fail to stain and remain as “ghost cells” in the peripheral smear. Because the KB test can determine the risk of isosensitization in Rh-negative gravidas, it is recommended for detecting imminent fetal exsanguination in injured pregnant patients who are Rh-negative in the second or third trimester. If positive, the KB test should be repeated after 24 hours to identify ongoing fetomaternal hemorrhage. The initial dose of Rh-immune globulin is 300 μg, with an additional 300 μg given for every 30 mL of fetomaternal transfusion estimated by the KB test. Although the KB test is a very sensitive marker for even a small amount of fetomaternal transfusion, its clinical utility in Rh-positive mothers is uncertain.28 Indeed, the usefulness of the KB test after injury has been challenged recently by several authors. Authors from the R Adams Cowley Shock Trauma Center in Baltimore reported that among 46 injured women who were KB-positive on admission, 44 had documented contractions.29 In that study, KB testing accurately predicted the risk of preterm labor after maternal trauma, whereas clinical assessment was insensitive in identifying women at risk for this complication. On the other hand, a recent study from Cincinnati documented that 5% of low-risk women had a positive KB test, compared to only 2.6% of injured patients.30 None of these positive results were associated with a clinical abruption or fetal distress. The authors concluded that the presence of a positive KB test alone does not necessarily indicate pathologic fetal–maternal hemorrhage in patients with trauma, and that its routine use after injury should be abandoned.31
Unfortunately, direct assessment of the fetus following trauma is somewhat limited. Currently, the most valuable information regarding fetal viability can be obtained by a combination of monitoring of the FHR and ultrasound imaging. Fetal heart tones can be detected with a Doppler device around the 12th week of pregnancy. The normal FHR is between 120 and 160 beats/min. Because the fetal stroke volume is fixed, the initial response to the stress of hypoxia or hypotension is tachycardia. Severe hypoxia in the fetus, however, is associated with bradycardia (FHR <120 beats/min) and should be recognized as fetal distress, demanding immediate attention. Initial FHR monitoring of all pregnant patients with potentially viable pregnancies (i.e., those that would survive if emergency delivery was required) is indicated, even following relatively minor abdominal trauma. This monitoring is best accomplished using cardiotocographic (CTM) devices, which record both uterine contractions and FHR. A lack of variability in heart rate may also indicate fetal distress, and if there is no response to conservative measures such as fluid administration, increasing inspired oxygen, or change in maternal position, an emergency delivery should be considered (Fig. 37-2).
FIGURE 37-2 (A) Cardiotocographic strip demonstrating poor beat-to-beat variability in the fetus. (B) Return of beat-to-beat variability after resuscitation; variable decelerations with uterine contractions are within normal limits.
Blunt trauma to the abdomen can result in uterine rupture, but this event is uncommon, unlikely to be missed, and usually rapidly fatal for the fetus. A much more common event is placental separation from the uterus as the result of the shearing forces following blunt injury. This separation is termed placental abruption. Major cases of placental abruption (i.e., >50% separation) are uniformly fatal for the fetus, but more minor cases may initially go undetected. Vaginal bleeding is an unreliable sign of placental abruptions, occurring in only 35% of cases.25 On the other hand, in patients with placental abruption following trauma, CTM will detect early fetal distress, often manifested as a decelerated heart rate associated with uterine contractions. Most cases of placental abruption become evident within several hours of trauma, although late cases have been reported.25,32,33 A minimum of 24 hours of CTM is recommended for patients with frequent uterine activity (≥6 contractions per hour), abdominal or uterine tenderness, vaginal bleeding, or hypotension.34 A study of 271 pregnant patients who had sustained blunt trauma identified the following risk factors for fetal loss: ejections, motorcycle and pedestrian collisions, maternal tachycardia, abnormal FHR, lack of restraints, Injury Severity Score (ISS) >9, gestational age >35 weeks, and a history of assaults.35 Patients with any of these risk factors should be monitored for at least 24 hours. In the absence of these factors, asymptomatic trauma patients should undergo at least 6 hours of CTM prior to considering discharge. These patients should be counseled to observe for decreased fetal movement, vaginal bleeding, abdominal pain, or frequent uterine contractions, as partial placental lacerations have been reported to progress over time.36
Ultrasonography
High-resolution real-time ultrasonography (US) has proven valuable for the assessment of fetal age and well-being, recognition and categorization of fetal abnormalities, and treatment of disease processes in the unborn patient. In the trauma setting, US is used primarily to identify acute problems that may be due to maternal events such as placental abruption, placenta previa, or cord prolapse. Although placental abruption is difficult to detect, US can accurately locate the lower margin of the placenta and its relation to the cervical os, hence demonstrating placenta previa.37 Additionally, it is routine to evaluate the fetus for gestational age, cardiac activity, and movement. In a study of 216 patients with high-risk pregnancies, fetal biophysical profile scores corresponded well with perinatal outcome.38 US findings consistent with uteroplacental injury may include oligohydramnios secondary to uterine injury or ruptured membranes. Oligohydramnios should be suspected if less than a 1-cm layer of amniotic fluid surrounds the fetus.
Radiographic Examination
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