A woman who is 24 weeks pregnant is placed on an intravenous infusion of magnesium sulfate. What side effect should the nurse inform the patient that she might experience?

Choice A rationale Magnesium sulfate is a central nervous system depressant and a smooth muscle relaxant. While it can cause fluid shifts, it is not primarily known for causing urinary frequency. In fact, if therapeutic levels become too high, it can lead to decreased urinary output (oliguria) by inhibiting the renal system, thereby increasing the risk of magnesium toxicity. Urinary output is a key assessment for magnesium toxicity. Choice B rationale Magnesium sulfate acts as a peripheral vasodilator, causing relaxation of vascular smooth muscle, which leads to a decrease in systemic vascular resistance. This peripheral vasodilation causes a sensation of warmth and a visible flushing of the skin, particularly in the face and neck, due to increased cutaneous blood flow. This effect is a very common, expected side effect upon initiation of the infusion. Choice C rationale While not a primary, expected side effect, headaches are a generalized symptom that could potentially be associated with changes in blood pressure or fluid dynamics, but the prominent side effect from magnesium's vasodilation is the flush. Hypotension, stemming from vasodilation, is a more directly related cardiovascular effect than headache, which is not universally reported. Choice D rationale Nausea and vomiting are possible side effects of magnesium sulfate, linked to its general smooth muscle relaxing effects, potentially affecting gastrointestinal motility. However, the most immediate and common patient-reported side effect upon infusion is the warm flush due to its potent peripheral vasodilatory action, making the flush the most pertinent information to provide first.