Magnesium sulfate should be initiated at the beginning of labor induction or, in women scheduled to undergo elective cesarean section, at least 1 hour prior to surgery.
Excessive doses of magnesium sulfate can lead to toxicity that could prove fatal to the mother or fetus. Therefore, specific protocols should be used to monitor all women receiving this drug. All such patients should have their reflexes checked every hour, urine-out measured hourly, and respiratory rate monitored closely. Magnesium sulfate should never be given as an IV bolus. It is recommended that the loading and maintenance doses be prepared premixed in an IV solution to ensure the proper concentration. The solution should be infused using a standard infusion pump. Serum magnesium levels should be obtained on a regular basis only in women with abnormal renal function (serum creatinine of 1.2 mg or more per deciliter), reduced urine output (less than 100 mL in 4 hours), or absent reflexes. In these cases, the infusion of magnesium sulfate should be discontinued or reduced according to maternal serum level.
In general, magnesium will not reach toxic levels until 4 hours or more after a maintenance dose. If the patient develops muscle weakness (double vision, inappropriate speech, respiratory difficulty) or shallow or absent respiratory effort or cardiac arrest, discontinue magnesium sulfate immediately, administer 1 g calcium gluconate in an IV (slowly, over 5 to 10 minutes), and intubate and ventilate the patient artificially. Subsequent management depends on the magnesium level.
Diagnosis of abruptio placentae. The slightly increased risk of abruptio placentae in patients with hypertensive disorders is not related to hypertension, but rather to the presence of preeclampsia. The highest risk usually is seen in patients who are suffering or just suffered from convulsions or in women with HELLP syndrome. Thus, it is important to document that patients were notified to report the onset of abdominal tenderness or vaginal bleeding. Also, instruct nursing personnel to report these findings to the physician as soon as they occur. The physician should evaluate the patient immediately.
Early in labor, bleeding may signify a “bloody show,” particularly when it is minimal, brief, and not associated with uterine contractions or FHR patterns. Abruptio placentae should be suspected in the presence of tetanic contractions, more than 5 uterine contractions in 10 minutes, or repetitive late decelerations or fetal bradycardia. Also suspect abruptio placentae if bleeding is persistent in the absence of placenta previa.
Antihypertensive therapy
The objective of treating severe hypertension is to prevent cerebrovascular accidents without compromising uteroplacental blood flow, which is already reduced in severe preeclampsia-eclampsia. There is considerable confusion regarding what BP level to treat and the desired level to achieve and maintain during treatment. Though there is little to no information regarding what systolic BP level to treat, most studies and textbooks recommend treatment if it exceeds 110 mm Hg.2 Some require this elevation to persist for at least 6 hours, some for 1 hour, and others for 30 minutes. The general recommendation is to lower the diastolic level to below 100 mm Hg, keeping it between 90 and 100 mm Hg.1,2 A recent consensus report and American College of Obstetricians and Gynecologists (ACOG) practice bulletin recommend treating diastolic blood pressure levels as low as 105 to 110 mm Hg, but no specific time period is described.1,2 A review of all such recommendations—none of which are based on scientific data—found considerable inconsistencies. Nonetheless, these recommendations have prompted expert witnesses in several malpractice cases to testify that diastolic BP as low as 100 mm Hg and systolic BP as low as 160 mm Hg should be treated.
There is considerable confusion regarding what BP level to treat and the desired level to achieve and maintain during treatment.
Preeclampsia is characterized by endothelial cell injury as well as vasospasm. These vascular pathologic changes have been described in cerebral blood vessels using Doppler velocimetry, angiography, computerized tomography (CT) scanning, magnetic resonance imaging (MRI), and autopsy. Some of these patients are predisposed to cerebral ischemic changes and stroke as a result of the disease process itself. Also, some patients with severe preeclampsia-eclampsia will have thrombocytopenia and DIC because of either the illness’s progression or abruptio placentae. These patients also are predisposed to intracerebral hemorrhage at normal or mildly elevated blood pressures. Finally, some patients with preeclampsia have a propensity to develop cerebral complications because of the aforementioned abnormalities. In such cases, the presence of hypertension (usually fluctuating with wide pulse pressure) is the result of intracerebral hemorrhage, rather than the cause. Consequently, any aggressive or rapid reduction in maternal BP may result in reduced cerebral blood flow, producing cerebral ischemia to normal brain tissue.