Classification

The classification of hypertensive disorders in pregnancy is confusing because not all health care providers consistently use standard definitions. The classification system most commonly used in the United States is based on reports from the American College of Obstetricians and Gynecologists (ACOG, 2002) and the National High Blood Pressure Education Program (2000). This classification system is summarized in Table 12-1.

Pathophysiology

Preeclampsia can progress along a continuum from mild-to-severe preeclampsia to eclampsia. Current thought is that the pathologic changes that occur in the woman with preeclampsia are caused by disruptions in placental perfusion and endothelial cell dysfunction (Gilbert, 2011; Harvey and Sibai, 2013; Sibai, 2012). These changes are present long before the clinical diagnosis of preeclampsia is made (Roberts and Funai, 2009). Normally in pregnancy the spiral arteries in the uterus widen from thick-walled muscular vessels to thinner, saclike vessels with much larger diameters. This change increases the capacity of the vessels, allowing them to handle the increased blood volume of pregnancy. Because this vascular remodeling does not occur or only partially develops in women with preeclampsia, decreased placental perfusion and hypoxia result (Harvey and Sibai, 2013). Placental ischemia is thought to cause endothelial cell dysfunction by stimulating the release of a substance that is toxic to endothelial cells. This anomaly causes generalized vasospasm, which results in poor tissue perfusion in all organ systems, increased peripheral resistance and BP, and increased endothelial cell permeability, leading to intravascular protein and fluid loss and ultimately to less plasma volume. The main pathogenic factor is not an increase in BP but poor perfusion as a result of vasospasm and reduced plasma volume (Fig. 12-1) (Gilbert, 2011; Roberts and Funai, 2009). Fig. 12-2 demonstrates how endothelial cell dysfunction causes many of the common signs and symptoms of preeclampsia.

Reduced kidney perfusion decreases the glomerular filtration rate and can lead to degenerative glomerular changes and oliguria. Pathologic changes in the endothelial cells of the glomeruli (glomerular endotheliosis) are uniquely characteristic of preeclampsia. Protein, primarily albumin, is lost in the urine. Uric acid clearance is decreased, but serum uric acid levels increase. Sodium and water are retained. Acute tubular necrosis and renal failure may occur (Gilbert, 2011; Roberts and Funai, 2009).

Plasma colloid osmotic pressure decreases as serum albumin levels decrease. Intravascular volume is reduced as fluid moves out of the intravascular compartment, resulting in hemoconcentration, increased blood viscosity, and tissue edema. The hematocrit value increases as fluid leaves the intravascular space. Arteriolar vasospasm can lead to endothelial damage and increased capillary permeability, predisposing the woman to pulmonary edema (see Fig. 12-2) (Gilbert, 2011; Roberts and Funai, 2009).

Decreased liver perfusion can lead to impaired liver function and elevated liver enzyme levels. If hepatic edema and subcapsular hemorrhage develop, the woman may complain of epigastric or right upper quadrant pain. Hemorrhagic necrosis in the liver can result in a subcapsular hematoma, which is a rare occurrence (Gilbert, 2011). Rupture of a subcapsular hematoma is a life-threatening complication and a surgical emergency (see Fig. 12-2).

Neurologic complications associated with preeclampsia include cerebral edema and hemorrhage and increased central nervous system (CNS) irritability. CNS irritability manifests as headaches, hyperreflexia, positive ankle clonus, and seizures. Arteriolar vasospasms and decreased blood flow to the retina can lead to visual disturbances such as scotoma (dim vision or blind or dark spots in the visual field) and blurred or double vision (Gilbert, 2011; Roberts and Funai, 2009).

Traditionally preeclampsia was considered to affect the woman primarily, causing hypertension, proteinuria, and perhaps associated multisystem dysfunction. However, currently it is recognized that it can also primarily affect the fetus, resulting in fetal growth restriction, decreased amniotic fluid volume, abnormal fetal oxygenation, low birth weight, and preterm birth (Sibai, 2012).

HELLP Syndrome

HELLP syndrome is a laboratory diagnosis for a variant of severe preeclampsia that involves hepatic dysfunction, characterized by hemolysis (H), elevated liver enzymes (EL), and low platelet count (LP). It is not a separate illness. Specific laboratory findings are needed to diagnose HELLP syndrome and distinguish it from other serious diseases that share the same signs and symptoms. HELLP syndrome occurs in 0.5% to 0.9% of all pregnancies. Ten to twenty percent of women with severe preeclampsia develop it (Harvey and Sibai, 2013). Table 12-3 lists laboratory changes that occur in HELLP syndrome. Traditionally it was not diagnosed unless all three laboratory abnormalities were present. Recently, however, women who develop only one or two of the diagnostic laboratory values are being diagnosed with incomplete HELLP, partial HELLP, or the ELLP syndrome (Harvey and Sibai, 2013).

The pathophysiologic changes of HELLP syndrome occur as a result of arteriolar vasospasm, endothelial cell dysfunction with fibrin deposits, and adherence of platelets in blood vessels. Red blood cells are damaged as they pass through narrowed blood vessels and become hemolyzed, resulting in a decreased red blood cell and platelet count and hyperbilirubinemia. Endothelial damage and fibrin deposits in the liver lead to impaired liver function and can cause hemorrhagic necrosis. Liver enzymes are elevated when hepatic tissue is damaged (Gilbert, 2011).

HELLP syndrome usually develops during the antepartum period. The clinical presentation is often nonspecific. Most women with the disorder report a history of malaise, influenza-like symptoms, and epigastric or right upper quadrant abdominal pain. Symptoms tend to worsen at night and improve during the daytime. HELLP syndrome can progress rapidly (Harvey and Sibai, 2013).

HELLP syndrome appears to occur more frequently in Caucasian women than women of other races. A diagnosis of HELLP syndrome is associated with an increased risk for maternal death and adverse perinatal outcomes, including pulmonary edema, acute renal failure, disseminated intravascular coagulopathy (DIC), placental abruption, liver hemorrhage or failure, acute respiratory distress syndrome (ARDS), sepsis, and stroke (Sibai, 2012). The reported perinatal mortality rate ranges from 7.4% to 34%, with a maternal mortality rate of approximately 1% (Sibai, 2012). The rate of preterm birth in women with HELLP syndrome is approximately 70%, with 15% of these occurring before 28 weeks of gestation. Most of the perinatal deaths occur before 28 weeks of gestation in association with placental abruption or severe fetal growth restriction (Sibai, 2012).