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Management of the Injured Pregnant Patient

Georges Desjardins MD FRCPC, Assistant Professor of Anesthesiology
University of Miami, Miami, FL

Trauma has become the most frequent cause of maternal death in the United States of America. Although maternal mortality due to other causes such as infection, hemorrhage, hypertension, and thromboembolism, has declined over the years, the number of maternal deaths due to penetrating trauma, suicide, homicide and motor vehicle accidents has risen steadily. Accidental injuries occur in 6 to 7 % of all pregnant patients. Penetrating trauma accounts for as many as 36 % of maternal deaths. In the case of gunshot wounds to the pregnant abdomen, overall maternal mortality is low ( 3.9 % ). Fetal mortality, on the other hand, is high, ranging between 40 and 70 %.

Although the initial assessment and management priorities for resuscitation of the injured pregnant patient are the same as those for other traumatized patients, 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. The main principle guiding therapy must be that resuscitating the mother will resuscitate the fetus.

Fetal Physiology
The effect of trauma on pregnancy depends on the gestational age of the fetus, the type and severity of the trauma, and the extent of disruption of normal uterine and fetal physiology. The survival of the fetus depends on adequate uterine perfusion and delivery of oxygen. The uterine circulation has no autoregulation which implies that uterine blood flow is related directly to maternal systemic blood pressure, at least until the mother approaches hypovolemic shock. At that point, peripheral vasoconstriction will further compromise uterine perfusion. Once obvious shock develops in the mother, the chances of saving the fetus are about 20 %.

If fetal oxygenation or perfusion are compromised by trauma, the response of the fetus may include bradycardia or tachycardia, a decrease in the baseline variability of the heart rate, the absence of normal accelerations in the heart rate, or recurrent decelerations. It should be noted that an abnormal fetal heart rate may be the first indication of an important disruption in fetal homeostasis. During trauma resuscitation, evaluation of the fetus should begin with auscultation of heart tones and continuous recording of the heart rate.

Trauma to the uterus (direct or indirect) can also injure the myometrium and destabilize decidual lysosomes, releasing arachidonic acid that can cause uterine contractions, and perhaps inducing premature labor.

Maternal Physiology
Increases in cardiac output and blood volume begin early in the first trimester and are 30-40% above the nonpregnant state by 28 weeks. This relative hypervolemic state and hemodilution is protective for the mother because fewer red blood cells are lost during hemorrhage. The hypervolemia prepares the mother for the blood loss that accompanies vaginal delivery (500 ml) or cesarean section (1000 ml). However, almost 40% of maternal blood volume may be lost prior to the manifestation of signs of maternal shock.

Despite the increase in blood volume and cardiac output, the parturient is susceptible to hypotension from aortocaval compression in the supine position. Only about 10% of pregnant patients at term develop symptoms of shock in the supine position, but fetal compromise can be occurring even in the asymptomatic mother. Left uterine displacement increases cardiac output by 30% and restores circulation. Uterine displacement must be maintained at all times during resuscitation, transport and perioperatively for nonobstetrical surgery.

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%. Care should be taken to consider these anatomic changes when thoracic procedures such as thoracostomies are being performed. The most important respiratory change during pregnancy is the decrease in functional residual capacity (FRC). Beginning in the second trimester, there is a 20% decrease in FRC coupled with a 20% increase in oxygen consumption. In addition, 30% of parturients have airway closure during normal tidal ventilation in the supine position. All these changes predispose to rapid falls in PaO2 during periods of apnea or airway obstruction. Hence, supplemental oxygen is always indicated for these patients in the resuscitation room. Minute ventilation increases at term by 50% due to an increase in tidal volume, so normal PaCO2 falls to 30-32 mmHg with a slight compensatory decrease in plasma bicarbonate levels.

Increased levels of progesterone and estrogen inhibit gastrointestinal motility. In addition, there is a decrease competency of the gastroesophageal sphincter, which increases the potential for aspiration. As the uterus enlarges, it displaces the intestines upward and laterally, stretching the peritoneum and making the abdominal physical examination unreliable.

To accommodate both maternal and fetal metabolic and circulatory requirements, renal blood flow increases by 25 to 50% during gestation. Blood urea nitrogen (BUN) and serum creatinine are reduced. Also, the kidneys enlarge by hypertrophy and hyperemia as early as the 10th week of gestation secondary to hormonal and mechanical factors.

The neurologic changes of pregnancy include a 25 to 40% decrease in anesthetic requirements. This means that loss of consciousness can occur even at "sedative" doses.

General Approach to the Trauma Patient
The primary initial goal in treating a pregnant trauma victim is to stabilize the mother's condition. The priorities for treatment of an injured pregnant patient remain the same as those for the nonpregnant patient.

Primary Survey
As with any other injured patient, the primary survey of the injured pregnant patient addresses the airway/cervical spine control, breathing and circulation (ABC; volume replacement/hemorrhage control), with the mother receiving treatment priority. Supplemental oxygen is essential to prevent maternal and fetal hypoxia. Severe trauma stimulates maternal catecholamine release, which causes uteroplacental vasoconstriction and compromised fetal circulation. Prevention of aortocaval compression is also essential to optimize maternal and fetal hemodynamics. Pregnant patients beyond 20 weeks' gestation should not be left supine during the initial assessment. Left uterine displacement should be used by tilting the backboard to the left or as a final measure, the uterus can be manually displaced.

Hypovolemia should be suspected before it becomes apparent because of the relative pregnancy induced hypervolemia and hemodilution that may mask significant blood losses. Aggressive volume resuscitation is encouraged even for normotensive patients. The pneumatic antishock garment (PASG) may be used to stabilize lower extremity fractures and perhaps control hemorrhage. In the pregnant patient, inflation of the abdominal compartment of the PASG should be avoided because if compromises uteroplacental blood flow.

Secondary Survey
The secondary survey consists of obtaining a complete history, including an obstetrical history, performing a physical examination, and evaluating and monitoring the fetus. The obstetrical history is important because the identification of comorbid factors may alter management decisions. A history of preterm labor or placental abruption puts the patient at increased risk for the recurrence of the condition. The obstetrical history should include the date of the last menstruation, expected date of delivery and any problems or complications of the current and previous pregnancies. Determination of the uterine size provides an approximation of gestational age, i.e. measurement of fundal height is a rapid method for estimating fetal age. Determination of fetal age and hence of fetal maturity is an important factor in the decision approach regarding early delivery.

The fetus is usually considered viable when it has a 50% chance of extrauterine survival. If neonatal facilities are available, this usually means at 25 to 26 weeks' gestation or an estimated weight of 750 g. More aggressive institutions use 24 weeks' gestation or an estimated weight of 500 to 600 g as the cut-off point, although chances of survival are then reduced to 20 to 30%. It should be noted that, even with the best of ultrasound dating criteria, unless the time of conception is known exactly, the assignment of gestational age is subject to 1 to 2 weeks of uncertainty. Decisions on fetal viability are made on the basis of the best gestational age available. When estimating the fetal age in the resuscitation area, a rough guide might be that when the fundus of the uterus extends beyond the umbilicus, the fetus is potentially viable.

Pelvic and rectal examinations should be performed. Aside from the usual secondary survey, assessment of the injured pregnant patient should rule out vaginal bleeding, ruptured membranes, a bulging perineum, the presence of contractions, and an abnormal fetal heart rate and rhythm.

Fetomaternal hemorrhage (FMH), the transplacental hemorrhage of fetal blood into the normally separate maternal circulation, is a unique complication of trauma during pregnancy. The reported incidence of FMH after trauma is 8 to 30%. There is no real correlation between severity of trauma, gestational age and frequency and volume of FMH. Complications of FMH include Rh sensitization in the mother, fetal anemia, fetal paroxystic atrial tachycardia or fetal death from exsanguination. In theory, FMH is possible by the 4th week of gestation; some say that FMH becomes a concern after 12 weeks gestation when the uterus rises above the pelvis and becomes an organ susceptible to direct trauma. FMH is detected by the Kleihauer-Betke (KB) acid elution technique on maternal blood. Upon examination, adult cells remain colorless while fetal red cells turn bright purple-pink. The ratio of fetal cells to maternal cells is recorded, enabling calculation of the volume of fetal blood leaked into the maternal circulation:

Most clinical laboratories will screen 1000 red blood cells taken from the mother. A maternal blood volume of 5 liters is commonly assumed in laboratory formulas so that one fetal cell per 1000 cells counted corresponds to a FMH of 5 ml. Unfortunately, the amount of FMH sufficient to sensitize most Rh-negative women is well below the 5-ml sensitivity level of the typical laboratory's KB test. As little as 1 ml of Rh-positive blood can sensitize 70% of Rh-negative women. Currently, several commercial kits expedite and simplify the test process. Unfortunately, the sensitivity of all the KB test is relatively low. Therefore, all Rh-negative mothers who present with a history of abdominal trauma should receive one 300-ug prophylactic dose of Rh immune globulin (anti-D immunoglobulin; Rhogam) within 72 hours of the traumatic event. Although controversial, we believe that the KB test should be reserved for Rh-negative women who are at risk for massive FMH that will exceed the efficacy of one dose of immune globulin, i.e. more than 30 ml. According to some studies, fewer than 1% of all trauma cases and only 3.1% of major trauma cases exceed the coverage of one 300-ug Rh immune globulin dose. As a general rule, 300 ug of Rh immune globulin should be given for every 30 ml of fetal blood found in the maternal circulation. The KB test is probably unnecessary before 16 weeks' gestation because the fetal blood volume is below 30 ml before this gestational age. For cases of documented FMH, some studies recommend repeating the KB test in 24 hours to check for increased bleeding.

Fetal Assessment
Fetal evaluation begins with checking fetal heart rate and noting fetal movement. Fetal heart tones can be detected by auscultation or doppler probe. This should be done early in the secondary survey and repeated frequently. The normal range for the fetal heart rate is 120 to 160 beats/minute. Continuous electronic fetal heart-rate monitoring (EFM) remains the most widely used modality for evaluation of the fetus, and is an adjunct to the monitoring of the maternal condition. The use of EFM permits prompt identification of the fetus at great risk for asphyxia and fetal death. Any viable fetus of 24 or more weeks' gestation requires monitoring after a trauma event. This includes patients with no obvious signs of abdominal injury because direct impact is not necessary for fetoplacental pathology to be present.

Controversy exists concerning the duration of fetal monitoring following a traumatic event to identify potential trauma-related fetal problems. The objective of the monitoring period is to identify premature labor, abruptio placenta and fetal distress. The combination of high-resolution real-time ultrasonography and cardiotocographic monitoring seems to have the highest sensitivity and specificity. They should both be instituted as soon as feasible without interfering with maternal resuscitative efforts.

The most common obstetric problem caused by trauma is uterine contractions. Myometrial and decidual cells, damaged by contusion or placental separation, release prostaglandins that stimulate uterine contractions. Progression to labor depends upon the size of uterine damage, the amount of prostaglandins released, and the gestational age of the pregnancy. Some studies question the routine use of tocolytics for premature labor after trauma because the majority (90%) of contractions stop spontaneously and those contractions that are not self-limited are often pathological in origin, thus, contraindications to tocolytic therapy.

Placental abruption after trauma occurs in 2 to 4% of minor accidents and in up to 50% of major injuries. Separation results as the inelastic placenta shears away from the elastic uterus during sudden deformation of the uterus. Abruption can occur with little or no external signs of injury to the abdominal wall. Maternal mortality from abruption is less than 1%, but fetal death ranges from 20 to 35%. Clinical findings that indicate abruption include vaginal bleeding, abdominal cramps, uterine tenderness, amniotic fluid leakage, maternal hypovolemia, a uterus larger than normal for the gestational age, or a change in the fetal heart rate. When present after trauma, vaginal bleeding is a ominous sign often indicative of placental separation. The first-line test to try to confirm the presence of abruption is the transabdominal ultrasound. Unfortunately, it is less than 50% accurate. In general, cardiotocographic monitoring is more sensitive in picking up placental abruption by fetal distress than ultrasound is by visualization. Most cases of abruption become evident within several hours after trauma. Cardiotocographic monitoring should be started in the resuscitation room and continued for a minimum of 4 hours. A minimum of 24 hours of cardiotocographic monitoring is recommended for patients with frequent uterine activity ( more than 6 contractions per hour ), abdominal or uterine tenderness, ruptured membranes, vaginal bleeding, or hypotension. For patients without any of these signs or symptoms, normal findings on the cardiotocographic monitor for at least 4 hours duration and a normal ultrasound, discharge may be considered. Fetal distress is associated with placental abruption 60% of the time and immediate intervention is required.

In the trauma setting, ultrasound may help identify other problems related to the maternal event besides placental abruption such as cord prolapse and placenta previa. It is also routine to evaluate the fetus for gestational age, cardiac activity and movement. If time permits, a complete biophysical profile may be performed.

Diagnostic Modalities/Radiation Exposure
Following maternal stabilization and assessment, and fetal evaluation, the extent of maternal and fetal injury is determined with the help of specific diagnostic modalities. Sensitivity to radiation is greater during intrauterine development than at any other time of life. Although there is much concern about radiation exposure, a diagnostic modality deemed necessary for maternal evaluation should not be withheld on the basis of its potential hazard to the fetus.

The fetal dose of radiation received in individual cases may vary by a factor of 50 or more, depending on the equipment used, technique used, number of radiographs done in a complete study, maternal size, and fetal/uterine size. In general, x-ray beams aimed more than 10 cm away from the fetus are not dangerous.

The major effects of exposure to the fetus include congenital malformations, growth retardation, postnatal neoplasia, and death. In the first week of life, before implantation, the embryo is very sensitive to lethal effects of radiation but has a low probability of sustaining teratogenic or growth-retarding effects if it is able to implant and grow. During major organogenesis of the 2nd to 7th weeks, the embryo is sensitive to the teratogenic, growth-retarding, lethal, and postnatal neoplastic effects of radiation. Organs are less sensitive to radiation teratogenesis in the 8th to 40th weeks, but growth retardation, central nervous system dysfunction, and postnatal neoplastic effects may occur. Studies show that exposure of the fetus to less than 5 to 10 rad (5000 to 10000 mrad) causes no significant increase in the risk of congenital malformations, intrauterine growth retardation, or miscarriage. Although this does not mean that there are definitely no risks in exposures less than 5 rad, it does mean that this level of radiation carries little risk for the fetus when compared to spontaneous risks. At a radiation dose of 15 rad, there is approximately a 6% chance that the child could develop severe mental retardation, a less than 3% chance of developing childhood cancer, and a 15% chance of having a small head size.

When performing radiographic evaluation of the mother, fetal irradiation should be minimized by shielding the abdomen when feasible with a lead apron. When many radiographs are required over a long period, a thermoluminescent dosimeter may be attached to the patient to serve as a guide to the dosage of radiation delivered. As a guide to physicians, reports from some studies indicate that the radiation dose from a plain AP chest x-ray is in general below 0.005 rad, a pelvic film below 0.4 rad, CT-scan of the head (1-cm slices) 0.05 rad, CT-scan of the upper abdomen (20 1-cm slices) below 3.0 rad and CT-scan of the lower abdomen (10 1-cm slices) 3.0 to 9.0 rad.

Blunt Abdominal Trauma
There are several important considerations when addressing blunt thoracoabdominal trauma in the pregnant patient. The physical examination may be unreliable because the enlarged uterus displaces the abdominal content and stretches the peritoneum thus perhaps diminishing the response to peritoneal irritation. The evaluation of possible injury to the abdomen is different because of the presence of the gravid uterus. The preferred diagnostic modalities for evaluation during the first trimester of pregnancy are ultrasound, diagnostic peritoneal lavage (DPL), and CT-scan, in that order. Because the first trimester is the period of organogenesis, ultrasound is preferable for the detection of hemoperitoneum. Because of its sensitivity, DPL can be used to evaluate the abdomen using the supraumbilical, open technique to avoid injury to the gravid uterus. The major disadvantage of DPL with respect to the pregnant patient is its invasiveness. If CT-scan is necessary, both oral and intravenous contrast media should be administered. During the second trimester, ultrasound or CT-scan may be used to evaluate the abdomen. DPL may be difficult to perform because the enlarged uterus may interfere with the dependent catheter position and return of fluid. On the other hand, several studies have shown its safety and usefulness. During the third trimester, the injured pregnant patient can best be assessed by ultrasound or CT-scan.

Although motor vehicle accidents are the most common cause of serious blunt trauma in pregnancy, assaults, abuse and falls are frequent. In addition to maternal mortality from blunt trauma, which is estimated to be about 7%, the fetus is at significant risk, especially if placental abruption, placenta previa, or uterine rupture occur.

Penetrating Thoracoabdominal Trauma
As mentioned before, as pregnancy progresses, intra-abdominal organs change position, with important implications (Figure 1). Because the bowel is pushed upward by the enlarged uterus, penetrating injury to the upper part of the abdomen is more likely to be associated with multiple gastrointestinal injuries. Organs involved in decreasing frequency are the small bowel, liver, colon, and stomach. During the third trimester, injuries to the lower quadrants of the abdomen almost exclusively involve the uterus. This may be advantageous to the mother because the uterus and amniotic fluid absorb most of the energy of the missile, resulting in less destruction to other organs. If the uterus is involved in penetrating trauma, fetal injury may occur in 60 to 90% of cases. Gunshot wounds to the uterus carry a maternal mortality of 7 to 9% and a fetal mortality of around 70%. Fetal mortality is higher if injury is caused before 37 weeks of gestation.

When evaluating the pathway of a bullet, radiographs (anteroposterior and lateral views) of the chest and abdomen, with the entrance and the exit wounds marked with paper clips may help the physicians. Some controversy exits but the prevailing opinion at this time is that pregnant women with gunshot wounds to the abdomen should generally undergo mandatory celiotomy. Stab wounds to the abdomen are managed similarly in pregnant and nonpregnant patients if signs of obvious intra-abdominal injury are present (shock, peritoneal signs, evisceration) or positive investigation.

A midline celiotomy should be performed, with exploration as in the nonpregnant state. If extrauterine intra-abdominal injuries are identified, organs are repaired or resected in the usual manner. Whenever the enlarged uterus interferes with adequate examination or repair, cesarean section is required. Celiotomy alone does not justify cesarean section because it prolongs the operation and increases blood loss by at least 1000 ml. Specific indications for cesarean section during celiotomy include maternal shock and pregnancy near term, threat to life from exsanguination from any cause, mechanical limitation for maternal repair, irreparable uterine injury, instability in a potentially viable fetus, unstable thoracolumbar spine injury, and maternal death.

Burn Injury
Treatment priorities are the same when managing pregnant and nonpregnant burn victims. Maintenance of a normal intravascular volume, avoidance of hypoxia, and prevention of infection are important. Burned areas of tissue should be debrided and cleaned. Silver sulfadiazine cream should be used sparingly because of the risk of kernicterus associated with sulfonamide absorption.

In cases of electrical burns, fetal mortality is high at 73% even with a rather low electrical current because of the fetus' lack of resistance to electrical shock. This is probably related to the fact that the fetus is floating in amniotic fluid with a low resistance to current. No matter how trivial their injury may seem, fetal monitoring and ultrasound assessment are indicated for all pregnant victims of electrical shock.

Perimortem Cesarean Delivery
During maternal resuscitation, adequate oxygenation, fluid loading, and left lateral decubitus should be tried to see if maternal circulation can be improved. Maternal survival after delivery of the fetus during unsuccessful cardiopulmonary resuscitation (CPR) has been reported. If there is no response to advanced cardiac life support within a few minutes (2 to 3 minutes), maternal cardiopulmonary resuscitation must be continued, anterior thoracotomy with open-chest cardiac massage (OCM) but without aortic cross-clamping should be considered, and emergency cesarean section for a viable fetus should be performed.

Studies have shown that conventional external cardiac massage (ECM) becomes less effective as the patient approaches term because of mechanical factors. The only method of assessing adequacy of fetal oxygenation during CPR is to monitor fetal heart rate (FHR). Carotid pulse and end-tidal CO2 monitoring should be used to monitor adequacy of maternal vital organ perfusion during CPR.

When the gestational age is less than 24 weeks, emergency cesarean delivery is usually not performed because the fetus is too small to survive and the birth is unlikely to have much effect on maternal hemodynamics. However, when gestational age is greater than 24-25 weeks, emergency cesarean birth probably will favorably affect maternal or fetal outcome. At a gestational age of 26 to 32 weeks, when external cardiac massage is not effective, as indicated by failure to generate a carotid pulse, inadequate end-tidal CO2 levels, or fetal bradycardia, OCM should be seriously considered before an emergency cesarean section is performed. If OCM prove successful, the delivery may be delayed so that chances of postnatal survival improve. Even slight prolongation of fetal intrauterine life will probably improve the chances of fetal survival, especially when gestational age is less than 28 weeks. If, however, OCM proves to be ineffective, the fetus must be delivered immediately. After 32 weeks gestation, when ECM is not effective, an emergency cesarean section must be performed immediately. Delivering the infant improves maternal cardiac filling, thereby improving the success of CPR. The longer the delay between the onset of cardiac arrest and delivery, the less are the chances of fetal and maternal survival. If, however, the ECM appears to be effective, ECM may be continued for 5 minutes. If a spontaneous circulation is not restored within 5 minutes, an emergency cesarean delivery must be performed. If this fails to revive the mother, OCM may be considered. Ideally, personnel trained in neonatal resuscitation should be available to attend the infant.

Trauma has become the most frequent cause of maternal death in the United States of America. The main principle guiding therapy must be that resuscitating the mother will resuscitate the fetus.

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