Hypertension in pregnancy: Tailoring treatment to risk
Not all hypertensive gravidas should receive drug therapy. In fact, antihypertensive medications should be halted in some patients. Here, 2 experts present a comprehensive plan for high- and low-risk women.
Pathophysiology. In hypertensive encephalopathy, loss of autoregulation leads to generalized cerebral vasodilation. Under normal conditions, when the mean arterial pressure is between 60 and 130 mm Hg, patients maintain constant cerebral blood flow. In hypertensive patients, however, autoregulation occurs between mean arterial pressures of 110 and 180 mm Hg as a result of arteriolar thickening. When BP exceeds the ability of the vessels to autoregulate, blood flow hyperperfuses the brain, causing fluid to leak into the perivascular tissue and resulting in vasogenic cerebral edema. Altered vascular reactivity to normally circulating pressor agents, deficient levels of vasodilating prostaglandins, endothelial dysfunction, and activation of the coagulation cascade may further exacerbate this condition.28
Treatment options. Clinically, it may be impossible to differentiate hypertensive encephalopathy from eclampsia, and magnesium sulfate should be considered for seizure prophylaxis. The most frequently used antihypertensive medications for this syndrome are shown in TABLE 6. Nitroprusside lowers BP most predictably, but because of the associated risks of fetal cyanide toxicity, other medications may be more desirable first-line agents in the pregnant woman.
Importantly, because sudden drops in BP may impair cerebral perfusion, we recommend that the mean arterial pressure be lowered no more than 25% from baseline (TABLE 7). If pulmonary edema develops, oxygen and furosemide should be administered, and consultation with subspecialists considered. (We suggest such consultation for cases of renal dysfunction and cerebral complications, as well.) Because nitroprusside is both a vasodilator and a venodilator, it is an ideal agent in this situation.
TABLE 6
Medications for treating acute severe hypertension
| DRUG | DOSE | ONSET OF ACTION | DURATION OF ACTION | SIDE EFFECTS |
|---|---|---|---|---|
| Hydralazine | 5-10 mg IV every 20 min | 10-20 min | 3-6 h | Tachycardia Headache Flushing Angina |
| Labetalol | 20-80 mg IV every 10 min | 5-10 min | 3-6 h | Scalp tingling Vomiting Heart block |
| Sodium nitroprusside* | 0.25-5 mcg/kg/min | Immediate | 1-2 min | Nausea Vomiting Muscle twitching Thiocyanate and cyanide intoxication |
| Nicardipine* | 5-15 mg/h IV | 5-10 min | 1-4 h | Tachycardia Headache Phlebitis |
| *Drugs to use in the presence of hypertensive encephalopathy. | ||||
TABLE 7
Principles of management for severe hypertension and encephalopathy
Acute severe hypertension
|
Hypertensive encephalopathy
|
| *Lower mean arterial pressure no more than 25% from baseline. |
Postpartum management
Monitor BP for at least 48 hours. Women with high-risk chronic hypertension are more likely to suffer postpartum complications such as pulmonary edema, hypertensive encephalopathy, and renal failure than normotensive patients.8 This risk is even higher when these women also have target organ involvement, superimposed preeclampsia, abruptio placentae, morbid obesity, or longstanding hypertension.
In these patients, BP must be closely monitored and controlled for at least 48 hours after delivery. Intravenous labetalol or hydralazine can be administered for acute elevations of BP29; diuretics should also be used for women with circulatory congestion and pulmonary edema.30
Methyldopa remains the first-line agent for breastfeeding patients without compelling indications for another drug.
Oral antihypertensive therapy may be needed to maintain BP control. In choosing the appropriate agent, it is important to consider whether factors compel the choice of one medication over another. For example, for patients with a history of myocardial infarction, beta blockers and ACE inhibitors are excellent choices to decrease mortality.31 In patients with diabetes mellitus, as mentioned earlier, ACE inhibitors offer a renoprotective effect.10
Consider drug concentrations in breast milk. Another significant consideration in the postpartum period is whether the mother wishes to breastfeed her infant. All antihypertensive medications are found in breast milk to varying degrees,32 and the long-term effects of these medications on breastfeeding infants has not been specifically studied.
Because concentrations of methyldopa in milk are low and considered safe, it remains the first-line agent for patients without compelling indications for another antihypertensive drug. Concentrations of labetalol and propranolol also are low in breast milk; therefore, these may be better choices than atenolol and metoprolol, which are more highly concentrated in breast milk.12
Although diuretic agents have low concentrations in breast milk, they may decrease milk production.32
Little information exists regarding the excretion of calcium-channel blockers in breast milk, but no untoward effects are apparent.33 ACE inhibitors and angiotensin II receptor antagonists should be avoided because of potential deleterious effects on neonatal renal function, even though their concentrations in breast milk appear to be low. If ACE inhibitors are indicated for the breastfeeding mother, current data suggest that captopril and enalapril are safe.34
The authors report no financial relationship with any companies whose products are mentioned in this article.
