The most prevalent changes during pregnancy occur in the cardiovascular system. Why all these alterations are important to you when you try to resuscitate a pregnant woman suffering a penetrating trauma? The increase in total blood volume, plasma volume, heart rate, stroke volume, and cardiac output, as well as the decrement in blood pressure, and central venous pressure, can interfere with assessment of the hemodynamic status of your patient.

Blood pressure is lower during pregnancy due to the decreased systemic vascular resistance owing to progesterone-induced vasodilation and due to the low resistance of the placental bed.

The increase in heart rate is the result of the estrogen-mediated increases in myocardial alpha receptors. The normal ECG changes in pregnancy include sinus tachycardia; left axis deviation (15°–20°); ectopic beats; Q wave in leads III and aVF; inverted or flattened T waves in leads III, V1, and V2; and unspecific ST changes.

Volume loss may be underestimated and hemodynamic instability signs may not be apparent until your patient has lost over 30 % of her total blood volume. If blood loss exceeds 2,500 mL, then pregnant patient’s condition can deteriorate extremely rapidly. Also, uterine blood flow comprises about 20 % of cardiac output, has no autoregulation, and is dependent on maternal mean arterial blood pressure, but you have to keep in mind that the fetus may be at risk even with no maternal signs of hypovolemia, while after their appearance the fetus is in jeopardy. So, you cannot rely on hemodynamic stability as an indicator of maternal blood loss, and it is reasonable to overhydrate in order to prevent hypoperfusion of the uteroplacental circulation.

The confusion can be even greater if you do take into consideration the “physiologic anemia” of pregnancy, as maternal erythropoiesis increment does not keep pace with the increase of plasma volume. Hematocrit and hemoglobin values of 30 % and 10 g/dL, respectively, are considered normal. A smart enough approach is to compare, if available, the most recent laboratory exams, as a lot of pregnant women have hematocrit levels obtained as a part of routine care.

Also, colloid osmotic pressure declines progressively with advancing gestational age owing to the falling level of serum albumin.

The respiratory system also undergoes changes. Oxygen consumption is increased due to the augmentation of the metabolic demands of the growing breasts, uterus, placenta, and fetus, and the partial pressure of oxygen (PaO₂) rises in order to maintain adequate oxygen delivery to all these tissues and fetus. Under this hypermetabolic status, you should always supply supplemental oxygen to the pregnant patient, even before you start your evaluation.

The growing uterus elevates the diaphragm. Subsequently, the respiratory reserve and residual volumes decline and result to the decrease of the functional residual capacity. So, you do not have as much time as you may think in case your pregnant patient has depressed respiration or is apneic.

These respiratory changes lead to an increase of the tidal volume and a slight or no increase of the respiratory rate, resulting to an upgrade of minute ventilation and lowering of the partial pressure of carbon dioxide levels (PaCO₂). So, you must consider any PaCO₂ levels between nonpregnant values. The pH remains, however, between normal values, because of the compensatory renal excretion of bicarbonate. As you already know, this is called compensated respiratory alkalosis. Keep in mind that this means that the pregnant patient has, already, a component of metabolic acidosis before her injury.

The renal perfusion is markedly increased during pregnancy, resulting in an increase in glomerular filtration rate. This leads to a drop in both serum creatinine and blood urea nitrogen levels, and values above 0.8 and 13 mg/dL, respectively, should be considered abnormal. Also, serum sodium is reduced. It is important if you want to evaluate a pregnant patient’s kidney function in trauma setting. Hydronephrosis, hydroureter, and urinary stasis are not uncommon owing to the relaxing effects of progesterone on smooth muscle, as well as to the growing uterus, predisposing to urinary infections.

Progesterone-mediated smooth muscle relaxation results to a decreased lower esophageal sphincter tone, and also the gastric empting is prolonged. In addition, stomach is displaced cephalad. Because of these changes, the risk of aspiration increases in a pregnant patient who cannot protect her airway in case of trauma. Remember that normal confusing complaints of the pregnant patient include nausea, vomiting, and abdominal discomfort. Bowel peristalsis is declined, too. As a consequence of this, there may be a prolonged period of postoperative ileus, nausea, and vomiting. Also, stasis of both gastric and gallbladder contents is common in pregnancy. Chronic distention of the parietal peritoneum by the expanding uterine contents produces less acute symptoms in cases of intraperitoneal bleeding, while the stretching of the peritoneum makes localizing pain difficult late in pregnancy.

Maternal white blood count increases in pregnancy. Levels between 5,000 and 30,000 cells per cubic milliliter (cells/mm³) are considered normal (up to 16,000 cells/mm³ during 1st and 2nd trimesters and up to 20,000 – 30,000 cells/mm³ during labor). Platelets range as in the nonpregnant status while at the lowest values. The levels of fibrinogen upgrade twofold times (normal values for pregnancy are more than 200 mg/dL) compared with nonpregnant measurements, and most procoagulant factors are increased, too. This seems to be beneficial for the pregnant patient in achieving hemostasis after trauma. But, also, you should carefully evaluate normal or low values of fibrinogen, with elevated fibrin degeneration products, and below normal values of platelets, as suggestive of disseminated intravascular coagulation (DIC). Another issue needed to be considered is that the increased procoagulant factors, in addition to the venous stasis in the lower extremities during pregnancy, place pregnant patient at risk for deep venous thrombosis and pulmonary embolism (DVT/PE). Therefore, when not contraindicated, DVT/PE prophylaxis should be considered.

Pregnancy alters the pattern of injury as gestation advances. The risk of trauma of fetus increases with gestation age. Fetal death is the result of direct fetal injury or preterm delivery. Before 13 weeks of gestation, the uterus is not yet an abdominal organ and is protected by the pelvic bones. Fetal loss in the first trimester is the result of maternal hypotension or death rather than a result of direct trauma. As the uterine enlarges, it and its contents occupy more and more space in the abdominal cavity, and it displays the bowel cephalad. This is protective regarding the bowel, but the uterus and fetus are more vulnerable to injury. The incidence of visceral injury with penetrating trauma in pregnancy is 16–38 %, compared with 80–90 % in nonpregnant population. Also, there are a thinning of the uterine wall and relative decrease in amniotic fluid volume with gestation age advancement, contributing to fetal vulnerability. Penetrating injuries in their majority involve uterine wall or uterine wall and fetus. The density of the uterus dissipates the energy of low-velocity traumas, but high-velocity ones are more devastating to mother and fetus. Maternal penetrating trauma in the upper abdominal area or posterior entry wounds are, however, associated with bowel or other visceral injuries; therefore, these injuries are explored surgically more often.

The bladder is displaced cephalad, too, making it susceptible to direct injury. So, you have to remember that in case of hematuria.

It is recognized that most pregnant trauma victims should be transported to a trauma center. Prehospital findings such as tachycardia (>110 beats/min), chest pain, loss of consciousness, and third trimester pregnancy have been independently associated with the need for care in a trauma center. The evaluation and management of these patients require a multidisciplinary approach. The trauma surgeons, the obstetricians, and maternal-fetal medicine specialists, emergency medicine technicians, emergency room physicians and nurses, anesthesiologists, and pediatricians are all members of a large collaborating team with the same intent, the rescue of mother and fetus. Treatment protocols regarding penetrating injuries are the same for the pregnant patient. Between your treatment options are immediate laparotomy and surgical exploration, laparoscopy, local wound exploration, diagnostic peritoneal lavage, CT imaging, and observation in an intensive care setting with continuous fetal monitoring and serial evaluations.