Regimens to lower BP safely
It is imperative that blood pressure be lowered in a measured and safe manner, not to exceed a drop of 25% to 30% in the first 60 minutes, and not to drop below 150/95.4 Medications available for blood pressure reduction are listed in the Clip-and-save chart above.5
Every effort must be made to not overcorrect the hypertension. Too swift or too dramatic a reduction in blood pressure can have untoward consequences for both mother and fetus, including but not limited to acute fetal distress secondary to uteroplacental underperfusion, and the possibility of maternal myocardial or cerebral infarction. For these reasons, short-acting intravenous agents are recommended to treat hypertensive emergencies, and oral or sublingual compounds are to be avoided because they are more likely to cause precipitous and erratic drops in blood pressure.6
Pulmonary edema is not uncommon, due to capillary leakage and myocardial dysfunction. Aggressive use of furosemide along with a rapidly acting antihypertensive drug will best allow for improvement of the clinical picture in a timely manner.
Acute management steps
Critical care facilities required. During the acute management phase, patients should be cared for in an intensive care unit (or a labor and delivery unit with critical care capabilities) under the direction of physicians skilled in managing critically ill patients. In most institutions, such management will include participation of anesthesiologists, maternalfetal medicine specialists, and nurses with critical care expertise.
Delivery considerations. During initial management, the patient should have continuous fetal heart rate monitoring. Under such extreme circumstances, it is often not possible to prolong a pregnancy that is remote from term. Delivery decisions will need to balance prematurity risks against maternal risks of continuing the pregnancy.
Hypertension is not a contraindication to glucocorticoids for accelerating lung maturation in the fetus and minimizing neonatal risk of intracranial hemorrhage and necrotizing enterocolitis.7 Adjusting for gestational age, neonates of preeclamptic mothers are afforded no additional maturity compared with neonates born prematurely for other reasons. Delay of delivery for 48 to 72 hours may not be possible in many cases, however. Once the patient is stabilized, delivery must be considered.
Start magnesium sulfate, continue antihypertensives
At this point, it is prudent to start magnesium sulfate to prevent eclampsia. In most cases, however, excluding a diagnosis of preeclampsia in a timely manner is nearly impossible. Under these circumstances, magnesium sulfate is recommended, in addition to continued antihypertensive medications, to maintain BP control.
Magnesium sulfate is best administered intravenously, preferably through an infusion pump apparatus. A loading dose of 4 to 6 g (I prefer 6 g) is given as a 20% solution over 15 to 20 minutes, and then a continuous infusion may be initiated at a rate that depends on the patient’s renal function. In a patient with normal renal function, a rate of 2 g per hour is appropriate, but may need to be reduced if acute renal failure ensues.
In a report of 3 recent cases, investigators found magnesium sulfate was beneficial for controlling the clinical symptoms of pheochromocytoma when conventional therapy was unsuccessful. The presenting symptoms of these nonpregnant patients included hypertensive encephalopathy (2 patients) and catecholamine-induced cardiomyopathy (1 patient).6
In general, however, the role of magnesium sulfate should be for preventing progression to eclampsia, and not for acute blood pressure control.
Delivery decisions
Vaginal delivery is often less hemodynamically stressful for the mother, but not always practical. Many cases are remote from term with the fetus in a nonvertex presentation, or the uterine cervix is unfavorable for induction, or a protracted attempt at labor induction may not be prudent.
Under such circumstances, cesarean delivery must be considered and may be preferable. The reasons relate to the underlying maternal condition that often includes some degree of uteroplacental insufficiency. Altered placental function, combined with extreme prematurity, often results in the fetus being unable to tolerate labor for very long, necessitating emergent cesarean under potentially less controlled circumstances. The anesthesiologist and others on the critical care team must review the optimal anesthesia technique.
In most circumstances, and in the absence of coagulopathy, regional anesthesia affords the best results. When regional anesthesia is not an option, balanced general endotracheal anesthesia with antihypertensive premedication using a short-acting agent may be the safest alternative.
Maintain postpartum vigil
With delivery of the fetus, there may be a temptation to be less rigorous in maintaining blood pressure control during the post-partum period. In patients with chronic hypertension without superimposed preeclampsia, this may be acceptable, as these patients better tolerate higher blood pressures and still maintain appropriate cerebral vascular autoregulation.