Delivery of the fetus to resolve preeclampsia.
• Magnesium Sulfate to Control Convulsions
Magnesium sulfate administered parenterally is an efective anticonvulsant that avoids producing central nervous system depression. It may be given intravenously by continuous inusion or intramuscularly by intermittent injection (Table 40-11). The dosages for severe preeclampsia are the same as for eclampsia. Because labor and delivery is a more likely time for convulsions to develop, women with preeclampsia-eclampsia usually are given magnesium sulfate during labor and for 24 hours postpartum.
In the United States, magnesium sulfate is almost universally administered intravenously. Of concern, magnesium sulfate solutions, although inexpensive to prepare, are not readily available in all parts of the developing world. And even when the solutions are available, the technology to infuse them may not be. herefore, it should not be overlooked that the drug can be administered intramuscularly and that this route is as efective as intravenous administration (Salinger, 20l3). In two reports from India, intramuscular regimens were nearly equivalent in preventing recurrent convulsions and maternal deaths in women with eclampsia (Chowdhury, 2009; lana, 20l3). hese observations comport with earlier ones from Parkland Hospital (Pritchard, 1975, 1984).
Magnesium suate is not given to treat hypertension. Magnesium most likely exerts a specific anticonvulsant action on the cerebral cortex. Typically, the mother stops convulsing after the initial 4-g loading dose. By an hour or two, she regains consciousness suiciently to be oriented to place and time.
he magnesium sulfate dosage regimens presented in Table 40-11 usually result in plasma magnesium levels illustrated in Figure 40-19. When magnesium sulfate is given to arrest eclamptic seizures, 10 to 15 percent of women will have a subsequent convulsion. If so, an additional 2-g dose of magnesium sulfate in a 20-percent solution is slowly administered intravenously. In a small woman, this additional 2-g dose may be used once, but it can be given twice if needed in a larger woman. In only 5 of 245 women with eclampsia at Parkland Hospital was it necessary to use alternative supplementary anticonvulsant medication to control convulsions (Pritchard, 1984). For these, an intravenous barbiturate is given slowly. Midazolam or lorazepam may also be given in a small single dose, but prolonged use is avoided because it is associated with a higher mortality rate from aspiration pneumonia (Royal College of Obstetricians and Gynaecologists, 2006).
TABLE 40-1 1. Magnesium Sulfate Dosage Schedule for Severe Preeclampsia and EclampSia
Give 4-to 6-g loading dose of magnesium sulfate diluted in 100 mL of IV fluid administered over 15-20 min Begin 2 g/hr in 100 mL of IV maintenance infusion. Some recommend 1 g/hr
Monitor for magnesium toxicity:
Assess deep tendon reflexes periodically Some measure serum magnesium level at 4-6 hr and adjust infusion to maintain levels between 4 and 7 mEq/L (4.8 to 8.4 mg/dL)
Measure serum magnesium levels if serum creatininen::1.0 mg/dL Magnesium sulfate is discontinued 24 hr ater delivery
Give 4 g of magnesium sulfate (MgS04·7H20 USP) as a 20% solution intravenously at a rate not to exceed 1 g/min