A 39-year-old G2P1001 at 39 weeks’ gestational age is sent to labor and delivery from her obstetrician’s office because of a blood pressure reading of 150/100 mm Hg obtained during a routine OB visit. Her baseline blood pressures during the pregnancy were 100 to 120/60 mm Hg to 70 mm Hg. On arrival to labor and delivery, the patient reports no headache, visual changes, nausea, vomiting, or abdominal pain. The heart rate strip is reactive and the tocodynamometer shows irregular uterine contractions. The patient’s cervix is 3 cm dilated. Her repeat blood pressure is 160/90 mm Hg. Hematocrit is 34.0%, platelets are 90,000 mL, SGOT is 22 units per liter, SGPT is 15 units per liter, and urinalysis is negative for protein.
The patient is successfully inducted and undergoes vaginal delivery. Postpartum, she is on magnesium sulfate for seizure prophylaxis. Her vital signs are—blood pressure 154/98 mm Hg, pulse 93 beats per minute, respiratory rate 24 breaths per minute, and temperature 37.3°C. She has adequate urine output at greater than 40 cc/h. On examination, she is oriented to time and place, but she is somnolent and her speech is slurred. She has good movement and strength of her extremities, but her deep tendon reflexes are absent.
Which of the following is the most likely cause of her symptoms?
A. Adverse reaction to hydralazineMagnesium therapy is typically continued for 24 hours postpartum in order to decrease the risk of seizures. This patient is showing signs of magnesium toxicity. The therapeutic range of serum magnesium to prevent seizures is 4 to 7 mg/dL. At levels between 8 mg/dL and 12 mg/dL, patellar reflexes are lost. At 10 mg/dL to 12 mg/dL, somnolence and slurred speech commonly occur. Muscle paralysis and respiratory difficulty occur at 15 mg/dL to 17 mg/dL, and cardiac arrest occurs at levels greater than 30 mg/dL.