Dissection of a Complicated Pregnancy

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.