Dissection of a Complicated Pregnancy

     "Medic One…..respond to a woman in labor. Reporting party states the patient is having trouble breathing." En route, you go over in your mind the procedure for problem deliveries. It was only two months ago that you assisted a mother in delivering a healthy baby girl at home, so the procedure is fresh in your mind. The night air is crisp, and the slight draft through your partially open window serves only to stimulate you in the early morning hours. Your EMT partner seems much calmer, most likely because he knows you'll be "in charge."

     On arrival, you make your way into the bedroom to find an obviously pregnant 21-year-old female lying on the bed writhing in pain and hyperventilating. She tells you that she woke up with pain in her back and it is steadily getting worse. You continue with your history-taking while assisting the patient onto your cot. As you peel back the covers to assist her, you notice a fluid stain in the middle of the bed. She tells you that at the height of pain, her water broke. Her husband verifies that his wife is 39 weeks along and the baby is due in "about a week." It's apparent that the baby is threatening to make an early appearance.

     As you assist her from the bed to the cot, she says she can't feel her legs. "They're just numb," she reports. You prepare to start an IV, which is made more difficult due to her constant movement. Your partner applies oxygen. When you ask the patient if she has the urge to push, she replies, "No, but my back is killing me!"

     "This woman is going to deliver the baby right here if we don't scoot to the hospital," you whisper to your partner. After a quick check for crowning, you load her into the ambulance. En route, she continues to complain of severe back pain.

     You attempt to time the pains so you can give the hospital some information about the frequency of contractions; however, there seems to be no consistency to the duration of the pains.

     On arrival at the hospital, you make your way to Labor & Delivery. The patient tells you she can't move her legs now, and she needs more help than usual moving onto the bed. You recite a quick report to the managing nurse, collect your equipment and head back up to the ambulance bay. You remember thinking, "A routine OB call." But days later, while talking with your medical director, you find out that the "routine" call turned out to be a pathophysiologic nightmare.

     The obstetrician assessed the patient to be in active labor with poor progression. The amniotic sac had ruptured and, due to the patient's severe pain, an emergency C-section was done. The obstetrician noted that the patient was complaining of difficulty moving and feeling her legs, but thought it might be due to fetal pressure on the lumbar nerves that supply the lower extremities. The C-section was "textbook" and an 8 lb., 3 oz. healthy-appearing infant was delivered.

     As the mother woke up from general anesthetic, she continued to writhe. The obstetrician noted that only her upper body was moving; no spontaneous movement was seen from her waist down. After a neurologic consultation and an emergent MRI, the worst was confirmed: The patient had an aortic dissection extending from the aortic valve to mid-abdomen. Emergency surgery was performed, leaving the patient with a new aortic valve and a Dacron graft to replace her ascending and a portion of descending aorta. The patient continued to recover in the CVICU.

AORTIC DISSECTION IN PREGNANCY
     Aortic dissection (AD) is a rare, although not unheard of, complication of pregnancy. It may present in multiple ways and can be, on first presentation, confused with the normal initiation of labor in a term pregnancy. As many as 50% of all cases of aortic dissection in females under age 40 are associated with pregnancy. Unchecked hypertension, Marfan's disease and histologic changes to the arterial walls mediated by progesterone and estrogen have all been implicated in aortic dissection in pregnancy. Acute aortic dissection is characterized by a tearing or separation of the intima lining of the aortic wall so that blood "dissects" down the false lumen (see Figure 1). There are generally three types of AD recognized: those involving the ascending aorta, descending aorta, or both (Figure 2). Blood vessels emanating from the aortic arch may be deprived of blood flow, risking ischemia downstream, usually in the extremities. In addition, the vessel wall may rupture, causing massive intrathoracic or intraabdominal hemorrhage and, almost assuredly, instantaneous death from exsanguination.

     Because back pain is a common complaint in pregnancy, AD can be difficult to diagnose, especially if not considered in the differential diagnosis. An EMS crew dispatched to a patient with a term pregnancy may find her complaining of back pain, and the weight of the fetus may be implicated as the cause of pain.

     So, how can a prehospital provider "make" the diagnosis, and what can be done prior to arrival at the hospital?

     First, the diagnosis must be considered. If you don't think about it, you can't diagnose it. If a pregnant patient complains of severe back pain, particularly upper back pain, acute AD should be considered. AD pain is different than that of active labor, as the patient will usually be moving constantly or writhing in pain, as opposed to the intermittent pains of labor. A history of Marfan's disease (a collagen-vascular disorder characterized by a tall, thin body habitus) or pregnancy-induced hypertension (PIH) may be obtained. Hypertension is almost always present, unless the false lumen occludes the artery supplying the extremity used to obtain blood pressure.

     You've loaded your patient and are en route to the hospital. You recall reading an article about acute AD in pregnancy and think that's what your patient may be experiencing. What can you do?

     After ensuring that your patient is getting oxygen and a patent IV is in place, direct your attention to the cardiovascular system. Check the pulses in all extremities. Are they present and equal in strength from side to side? Attempt to obtain a blood pressure in both arms. The systolic pressure should vary no more than 10–20 mmHg between arms. A discrepancy greater than 20 mmHg may indicate the presence of an AD that is at least partially occluding one of the main vessels from the arch of the aorta (Figure 3), such as occlusion of the left subclavian artery causing a lower blood pressure in the left arm. This, however, should not be considered the "rule," as AD is possible with equal bilateral blood pressures.

     Ischemia in the lower extremities may be recognized by poor capillary refill, cyanotic toes or mottling of the skin. A useful acronym for this is ILEAD: Ischemia of the Lower Extremity in Aortic Dissection. AD should be considered in a patient with evidence of lower extremity ischemia along with chest or upper back pain. Blood flow to the spinal arteries may produce a similar effect by compromising spinal cord function of the lower extremities.

     One of the main tactics for treating AD is lowering the blood pressure to minimize stress to the arterial walls and thereby decrease arterial pressure causing the luminal dissection. Depending on your EMS system, you may be asked to decrease the patient's blood pressure with medication. The safest drug to accomplish this is labetalol, which has both beta-blockade and alpha-blockade effects. It is typically ordered in 10–20 mg aliquots given every 30 minutes. Nitroglycerin is another drug that may be used for this purpose; however, it can produce a reflex tachycardia, so it is usually preceded by a true beta-blocker like esmolol to blunt this effect. The combination of nitroglycerin and esmolol is typically outside the realm of EMS practice. Labetalol remains the primary treatment modality for AD complicated by hypertension. Although labetalol is classified as a "C" drug in pregnancy (no studies have shown it to be harmful in pregnancy, although it is only recommended when the benefits outweigh risk), it has been given safely in pregnancy for many years and continues to be used by obstetricians for pregnancy-induced hypertension. The risk of administering any drug to decrease blood pressure is that blood flow to the uterus may also be compromised.

     The pain may become so intense it requires treatment with a narcotic, such as morphine. This can be titrated to effect, but it should be discussed with online medical control prior to administration.

     If time allows, obtain a 12-lead EKG. An ascending AD can be associated with dissection into a coronary artery, mimicking an acute ST-segment elevation myocardial infarction (STEMI). This can be fraught with problems, as the paramedic's first reflex would be to administer aspirin, which is contraindicated in both AD and pregnancy. It is also not uncommon with an extensive ascending AD to have aortic valve involvement, predisposing the patient to valvular incompetence and "flash" pulmonary edema. This should be treated aggressively with oxygen administration and continuous positive airway pressure (CPAP), if available. In this case, nitroglycerin may be administered to decrease preload to the heart and subsequently relieve pulmonary vascular congestion. In any case, the patient should be emergently transported to a facility offering high-risk pregnancy care, cardiovascular surgery and neonatal intensive care.

CONCLUSION
     Acute thoracic or abdominal AD (or both), especially in the term pregnancy patient, remains an elusive diagnosis due to the overlapping symptoms of active labor. Another condition that may be confused with AD is acute pulmonary embolism (PE). While usually causing chest pain and dyspnea, it can also be responsible for severe back pain, not unlike AD. There are no hard and fast rules for differentiating between AD and PE. Generally, these are difficult to diagnose without radiologic studies. Only by looking for the signs and symptoms known to be associated with AD and conveying your suspicions to the attending ED physician or obstetrician can you save the patient a significant morbidity and, quite possibly, a terrible mortality.

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Jim Morgan, DO, is an emergency medicine attending physician at Freeman Health System in Joplin, MO.