The objective of treating acute severe hypertension is to prevent potential cerebrovascular and cardiovascular complications such as encephalopathy, hemorrhage, and congestive heart failure (National High Blood Pressure Working Group, 2000). For obvious ethical reasons, there are no randomized trials to determine the level of hypertension to treat in order to prevent these complications. The point at which to begin antihyperten-sive drug therapy is not clear. Antihypertensive therapy is recommended by some for sustained systolic blood pressure values of >180 mmHg, and for sustained diastolic values of >110 mmHg. Some experts recommend treating systolic levels of >160 mmHg, others recommend treating diastolic levels of >105 mmHg, whereas others use a mean arterial blood pressure of >126—130 mmHg (ACOG Practice Bulletin, 2001; National High Blood Pressure Working Group, 2000). The definition of sustained hypertension is not clear and ranges from 30 min to 2 h.
The most commonly used and advocated agent for the treatment of severe hypertension in pregnancy is intravenous hydralazine given as bolus injections of 5—10 mg every 15—20 min for a maximum dose of 30 mg. Recently, several drugs have been compared to hydralazine in small, randomized trials. The results of these trials were the subject of a recent systematic review that suggested that intravenous labetalol or oral nifedi-pine are as effective as each other, and that these two drugs have fewer side effects than intravenous hydralazine (Duley et al., 2000). The recommended dose of labetalol is 20—40 mg IV every 10—15 min for a maximum of 220 mg, and the dose of nifedipine is 10—20 mg orally every 30 min for a maximum dose of 50 mg (National High Blood Pressure Working Group, 2000). We generally use sustained blood pressure values of >170 mmHg systolic or >110 mmHg diastolic to initiate therapy intrapartum. For women with thrombocytopenia and those in the postpartum period we use systolic values of >160 mmHg or diastolic of >105 mmHg.
Table 25.4. Acute treatment of hypertension
Onset of action
5-10 mg IV every 20 min up to max. dose of 30 mg
10-20 mg IV, then 40-80 mg every 10min up to max dose of 300mg
Continuous infusion 1-2mg min-1
10 mg po, repeated in 30 min prn, then 10-20 mg q 4-6h
0.25-5 mcgkg-1 min-1 IV infusion
Risk of fetal cyanide poisoning with prolonged treatment
Table 25.5. Chronic treatment with antihypertensive medications
Methyldopa Labetalol Thiazide diuretic Nifedipine
250-500 mg po q 6-12 h 100 mg po bid 12.5 mg po bid 10-20mg po q 4-6h
Our first line agent is IV labetalol, and if maximum doses are ineffective, oral nifedipine is added. Tables 25.4 and 25.5 list the most commonly used antihypertensive medications.
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