Extensive changes occur in the maternal cardiovascular system during pregnancy. Plasma blood volume increases 50%. Red blood cell volume increases 30%. The maternal heart rate is increased by 10% to 15%, and
maternal cardiac output is increased 30% to 50%. The end result of these adaptations is the ability to provide increased cardiac output, and oxygen and nutrient delivery, to the growing uterus and developing fetus. Any condition that causes a reduction in perfusion to the uterus is poorly tolerated by the fetus. Providers must be acutely aware that this increase in blood volume may initially mask a significant hemorrhage that may have significant consequences for both the mother and fetus. During pregnancy there is increased blood flow to the uterus. Every 8 to 11 minutes, the total circulating maternal blood volume flows through the uteroplacental bed, contributing to the potential for significant hemorrhage with any maternal abdominal trauma.

Pregnancy is considered a high-flow, low-resistance state. Under the influence of progesterone, the smooth muscles surrounding blood vessels are relaxed during pregnancy. This results in decreased systemic vascular resistance (SVR) and blood pressure that reaches its nadir in the second trimester. As the gestation progresses, SVR and maternal blood pressure gradually increase. Maternal blood pressure returns to prepregnancy levels by the end of the third trimester. During pregnancy the uteroplacental bed functions as a dilated, passive, low-resistance system. Perfusion pressure determines blood flow to the uterus and under normal circumstances there is no uteroplacental vasoconstriction to impede blood flow. Therefore, any condition that results in a decrease in maternal blood pressure, such as hemorrhage or hypovolemia, results in vasoconstriction of the uterine arteries and shunting of blood to the essential organs. This shunting of blood away from the uteroplacental bed has the compensatory effect of maintaining maternal blood pressure at the expense of the fetus. The increased blood volume of pregnancy and this physiologic shunting are what allow the maternal trauma patient to maintain relative physiologic stability until massive blood loss has occurred.⁸ Once tachycardia and hypotension develop, considered hallmark symptoms of blood loss, the care provider may already be behind with respect to resuscitative efforts.⁹ Therefore, tachycardia and hypotension in the pregnant trauma patient are clinically significant findings that require careful evaluation and should not be solely attributed to pregnancy.¹⁰

Additionally, maternal positioning has significant effects on maternal blood pressure and uterine blood flow. When the pregnant patient is placed in a supine position, the gravid uterus compresses the inferior vena cava. The end result of this compression is a decrease in venous return, a decrease in cardiac output, and a decrease in uterine blood flow, which can have profound effects on both normal and hemodynamically compromised patients. Thus, the supine position should be avoided. To avoid the supine position, providers may use a wedge or rolled blankets to tilt the spinal backboard in a 15 degree tilt.¹¹ If it is not possible to tilt the spinal backboard, then manual displacement of the uterus should be done. Care must be taken to ensure that the spine remains secure and aligned until a spinal injury is ruled out. These simple maneuvers are very effective in alleviating supine hypotension and its effect on uterine blood flow.

The maternal pulmonary system also undergoes significant adaptations that may affect trauma management in the pregnant patient. These adaptations occur to ensure that the developing fetus has adequate oxygen delivery and are discussed in detail in Chapter 5 of this text. As a result of these changes, the pregnant patient normally has a chronic compensated respiratory alkalemia that is reflected in the arterial blood gases.

The pregnant patient has diminished oxygen reserve and decreased blood buffering capacity. When caring for pregnant trauma patients, any acid–base balance disturbances should be evaluated, keeping in mind that a primary normal change in acid–base balance already exists. This leaves the pregnant trauma patient vulnerable to hypoxemia and less able to compensate when acidemia ensues.

A significant anatomic adaptation is the change in the location of the maternal diaphragm. As the uterus grows, the maternal diaphragm is displaced 4 centimeters above its normal location. This change in location must be considered if placement of a chest tube is necessary, to avoid injury to the diaphragm. If placement of a chest tube is performed, a higher insertion point should be utilized. In pregnant patients this insertion point is usually between the third and fourth intercostal space.

During pregnancy the bladder is displaced both anteriorly and superiorly by the growing uterus. The bladder essentially becomes an abdominal organ and much more vulnerable to injury. The renal pelvises and ureters are dilated secondary to relaxation of the smooth muscle and compression from the growing uterus. The gravid uterus may obstruct or impede urinary outflow. There is also an increase in renal blood flow, leading to an increase in glomerular filtration rate (GFR). This results in an increase in creatinine clearance during pregnancy. During pregnancy, a serum creatinine that would be considered normal in a nonpregnant patient may reflect seriously compromised renal function and requires further evaluation.¹²

The uterus increases dramatically in size as the pregnancy progresses. By 12 weeks gestation, the uterus moves out of the pelvis and becomes an abdominal organ, making it vulnerable to injury. In addition, because of the increased blood flow to the uterus during pregnancy, the likelihood of hemorrhage with any uterine injury or pelvic trauma is significantly increased.¹³

Secondary to these and other alterations during pregnancy, the potential for significant clinical problems exists in the pregnant trauma patient. A summary of these potential problems is presented in Box 21-1.

Initial prehospital care should include assessment of the clinical condition of the patient. If it is known that the patient is pregnant, transport to a level one trauma center with obstetric capabilities should be arranged, particularly if there is hemodynamic instability, loss of consciousness, or the fetus is viable. This assessment may not be possible if the patient is unable to communicate, is not visibly pregnant, or maternal obesity makes assessment of gestational age difficult.

Whenever possible, information related to the pregnancy should be sought by the initial responders and communicated to the accepting facility. This allows time for notification of both the obstetric and neonatal teams so that comprehensive, multidisciplinary care can begin immediately upon arrival at the trauma center. Vital signs should be obtained and symptoms assessed, with the knowledge that pregnant patients may not present in the same manner as nonpregnant patients.

If hemorrhage is suspected, two large bore (14 or 16 gauge) intravenous catheters should be placed and volume resuscitation initiated. Supplemental high flow oxygen via mask should be administered. When obstetric patients are placed on a spinal back board, a 15 degree lateral tilt should be maintained to avoid compression of the vena cava and aorta by the gravid uterus. Failure to properly position these patients can result in decreased uteroplacental perfusion as well as inadequate perfusion of other vital organs.

The primary survey is the systematic evaluation of a trauma patient performed according to standard Advanced Trauma Life Support (ATLS) protocols.¹⁴ This survey is accomplished within minutes and includes simultaneous assessment and interventions when significant, immediate, life-threatening injuries are present. Assessment and treatment priorities, in accordance with ATLS recommendations, are presented in Box 21-2.

The primary survey always begins with assessment of the patient’s airway. This includes the basic “look, listen, and feel” for movement of air. For the conscious patient, airway assessment can be accomplished at a glance; that is to say, the patient who is talking or shouting has an open, intact airway. An unconscious patient requires close assessment and may require assistance to obtain or maintain an open airway.

Protection of the airway is of the utmost importance. Maintenance of a patent airway and establishment of adequate ventilation and oxygenation may require intervention. If fetal hypoxemia is to be avoided, early aggressive maternal ventilatory support may be required. High flow oxygen via mask, if not already initiated, should be administered, even if there are no visible signs of respiratory distress. Oxygen demands are increased during pregnancy and traumatic injury further increases these demands. Pregnant trauma patients who have a respiratory rate of less than 12 breaths per minute or greater than 25 breaths per minutes may need additional intervention and support.

If airway patency is in doubt, use of a simple device such as an oropharyngeal airway may be sufficient. However, complete control of the airway is often required, in order to ensure adequate maternal oxygenation; therefore, endotracheal intubation may be necessary. Nasal intubation should be avoided in pregnant patients, since the increased vascularity in the upper airway and nares predisposes pregnant women to significant bleeding during this potentially traumatic procedure.

If endotracheal intubation is required, pre-oxygenation is essential, since the pregnant patient is vulnerable to rapid oxygen desaturation surrounding the period of time endotracheal intubation is performed.⁹ Placement of a pulse oximeter allows for assessment of arterial oxygen saturation (SaO₂) and detection of oxyhemoglobin desaturation. Since pregnant women are at increased risk for aspiration during intubation, placement of an oral or nasogastric tube for gastric decompression is an important safeguard. These measures, along with vigilant assessment and rapid intervention in the event of vomiting, may decrease the incidence of this very serious complication.

Assessment of bleeding and circulation are performed concurrently during the primary survey. Clinical parameters that are useful to assess circulation include heart rate, pulse quality, and capillary refill. These parameters reflect the adequacy of maternal perfusion. It is important to note that time-consuming traditional assessment of arterial blood pressure may not be necessary for patients who present with evidence of hypovolemic shock. For example, the presence of a palpable carotid artery pulse indicates a systolic arterial blood pressure of at least 60 mmHg, a palpable femoral pulse indicates a systolic pressure of at least 70 mmHg, and the presence of a palpable radial pulse indicates a systolic pressure of at least 80 mmHg. Traditional assessment of
arterial blood pressure should be performed for obstetric trauma patients as time permits.

When evaluating circulatory status, the physiologic changes of pregnancy cannot be ignored. The significant increase in maternal intravascular volume associated with normal pregnancy may mask hypovolemic shock, until significant blood loss has occurred. Care providers should assess for evidence of hemorrhage and initiate appropriate treatment when such evidence is present. Hypotension should be presumed to be secondary to hypovolemia, until proven otherwise.¹⁵ Significant compromise in uterine blood flow may exist, even with a normal maternal arterial blood pressure, because of the physiologic shunting that occurs to preserve blood flow to the heart, lungs, brain, and kidneys.

If not already in place, two large bore (14 to 16 gauge) intravenous catheters should be inserted and 1 to 2 liters of warmed crystalloid solutions should be infused. Normal saline or lactated Ringer’s solutions are the fluids of choice for volume resuscitation. In the face of continued hemorrhage and maternal instability, transfusion of O-negative blood should begin immediately, followed by type-specific or cross-matched packed red blood cells (PRBCs) and fresh frozen plasma as soon as it is available.