In our institutions, any patient who is taking antihypertensive medication and in whom we are entertaining a diagnosis of preeclampsia is recommended for hospitalization for the duration of her pregnancy or until a diagnosis of preeclampsia can be ruled out with reasonable certainty.
Expectant management beyond 37 weeks does not benefit mother or fetus
Because preeclampsia is a multisystem disease, it has maternal, placental, and fetal consequences. The cure for preeclampsia remains delivery of the placenta. Expectant management offers no maternal benefit, but does offer some potential neonatal benefits if prematurity is a concern. Once concerns about prematurity have been largely eliminated, generally by achieving a gestational age of 37 weeks, further expectant management is not indicated, offers little or no additional benefit to the fetus, and leaves both mother and fetus at risk.
Therefore, once the pregnancy reaches 37 weeks, delivery is recommended.
When preeclampsia is severe, and when it is superimposed in a patient who is taking antihypertensive medication, we generally do not continue the pregnancy beyond 34 weeks.4 In our institutions, most patients who are being expectantly managed for severe preeclampsia remote from term—and who have remained stable—are delivered between 32 and 34 weeks’ gestation, depending on the specific clinical circumstances.
CHALLENGE NO. 4: Controlling blood pressure
Cerebrovascular accident (stroke) is the leading cause of maternal mortality from preeclampsia in the United States. Not all cases can be prevented, but one suggested preventive strategy is adequate BP control. Some cases of stroke in the setting of preeclampsia will occur despite systemic BP readings that are not considered to be in a dangerous range. One reason may be an override of normal cerebral blood flow autoregulatory mechanisms, resulting in increased cerebral blood flow, rising cerebral perfusion pressures, and vessel rupture. Such occurrences may sometimes, but not always, be related to coagulopathy.
When a patient has elevated BP, generally defined as persistent systolic pressures above 160 to 170 mm Hg and persistent diastolic pressures above 105 to 110 mm Hg, antihypertensive therapy is indicated and should be administered in a timely fashion.
Labetalol, nifedipine, and hydralazine have all been used effectively in such acute settings, when administered parenterally (except nifedipine, which may be given orally) and when given in proper dosages (TABLE 3).
Avoid oral use of labetalol or hydralazine to treat acute hypertensive emergencies.
TABLE 3
Pharmacotherapy of acute hypertension
| Drug | Dosage | Directions |
|---|---|---|
| Hydralazine* | 5 mg IV | Repeat in 10 min, then give 10 mg IV every 20 min until BP stabilizes (140–150/90–100 mm Hg) |
| Labetalol* | 10–20 mg IV push | Repeat every 10-20 min, doubling the dosage each time until a maximum total cumulative dosage of 300 mg has been given |
| Nifedipine* | 10 mg | Repeat in 20 min for four doses (maximum 40 mg); then give 10–20 mg orally every 4–6 h to achieve a stable BP of 140–150/90–100 mm Hg |
| * If target blood pressure is not reached after the maximum dosage of an agent is given, then additional or alternative pharmacotherapy must be utilized. | ||
Goals for treatment
In the antepartum patient, the goal is to maintain systolic BP at 140 to 150 mm Hg and diastolic pressure at 90 to 100 mm Hg to keep from inadvertently inducing uteroplacental insufficiency secondary to reduced uterine blood flow.
In the delivered patient, the risk of mild hypotension is not quite as great, although an attempt to rapidly return the patient to her previous normal BP profile may cause symptomatic hypotension.
If a patient develops a true hypertensive crisis with hypertensive encephalopathy (which generally occurs at BPs exceeding 240/140 mm Hg), then emergent intervention with a rapidly acting agent such as sodium nitroprusside is necessary and should be managed by someone skilled in critical care and the use of such drugs.
CHALLENGE NO. 5: Preventing seizures
Magnesium sulfate is the drug of choice to prevent both initial and recurrent eclamptic seizures.5 Two large clinical trials ended any doubts about its efficacy, demonstrating its superiority over both phenytoin and diazepam in the settings of preeclampsia and eclampsia.
Magnesium sulfate is best administered intravenously (IV) via continuous infusion pump. An initial bolus of 4 to 6 g is given over 15 to 30 minutes; this amount does not need to be adjusted to the patient’s level of renal function. A continuous infusion of magnesium sulfate is usually initiated at a rate of 2 g/hour. It is this infusion dosage that may need to be altered, based on the patient’s urine output and renal function.
Evidence of magnesium toxicity includes:
- loss of deep-tendon reflexes
- respiratory depression
- blurred vision
- cardiotoxicity.