Explain the management of preeclampsia-related hypertension.
Control of hypertension in the parturient with preeclampsia is imperative since acute elevations of blood pressure can lead to cerebral hemorrhage, the leading cause of mortality. The patient’s blood pressure should be neither acutely decreased nor decreased to levels considered nor-mal for other parturients since a low blood pressure could compromise uteroplacental blood flow. Although MgSO4 causes vasodilation, it does not treat hypertension adequately and an alternative antihypertensive drug is usually needed. Also, as in any patient with hypertension, responses to both antihypertensive and pressor agents are exaggerated. Therefore, reduced doses of these agents should be used initially and the response noted prior to increasing the dose.
The most frequently used antihypertensive agent is hydralazine, which not only decreases blood pressure but also increases renal and uteroplacental blood flow. The tachycardia that occurs with the use of hydralazine can be treated with propranolol. Hydralazine is not the agent of choice in the acute situation since it takes 10–15 minutes before an effect is seen.
Nitroprusside, a potent arterial vasodilator, is often used when immediate control of blood pressure is required. It is administered by infusion making it easy to titrate to effect. Nitroprusside, however, crosses the placenta and cyanide toxicity has been described in the neonate after prolonged infusion in the mother. Trimethaphan, a ganglionic blocker, has also been used with good success in the emergent situation.
Nitroglycerin, a venous dilator, is useful when tight con-trol of blood pressure is required for prolonged periods. Nitroglycerin is not as potent as nitroprusside but is easy to titrate and has minimal effect on the fetus.
Propranolol, diazoxide, methyldopa, and captopril are generally not used in the patient with preeclampsia because of their adverse side-effects (Table 60.3).