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A 48-year-old woman develops constipation postoperatively and self-medicates with milk of magnesia. She is noted to have an elevated serum magnesium level. Which of the following represents the earliest clinical indication of hypermagnesemia?

a. Loss of deep tendon reflexes

b. Flaccid paralysis

c. Respiratory arrest

d. Hypotension

e. Stupor

The answer is a. The earliest clinical indication of hypermagnesemia is loss of deep tendon reflexes, which tends to be seen with a modest hypermagnesemia, over about 4 mEq/L. States of magnesium excess are characterized by generalized neuromuscular depression. Clinically, severe hypermagnesemia is rarely seen except in those patients with advanced renal failure treated with magnesium-containing antacids. However, hypermagnesemia is produced intentionally by obstetricians who use parenteral magnesium sulfate (MgSO4) to treat preeclampsia. MgSO4 is administered until depression of the deep tendon reflexes is observed. Greater elevations of magnesium produce progressive weakness, which culminates in flaccid quadriplegia. Other cardiorespiratory complications include respiratory failure or arrest secondary to respiratory muscle dysfunction, and hypotension may be secondary to the direct arteriolar relaxing effect of magnesium. Changes in mental status occur in the late stages of the syndrome and are characterized by somnolence that progresses to coma.

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Symptoms of Hypermagnesemia
Magnesium level (mEq/L) Manifestation(s)
1.5–2.1 Normal
2.1–4.2 Typically asymptomatic
4.2–5.8 Lethargy, drowsiness, flushing, nausea and vomiting, diminished deep tendon reflexes
5.8–10 Somnolence, loss of deep tendon reflexes, hypotension, ECG changes
>10 Complete heart block, cardiac arrest, apnea, paralysis, coma
Source: McEvoy C, Murray PT. Electrolyte disorders in critical care. In: Jesse B. Hall, et al. (eds.). Principles of Critical Care, 4th ed. New York, NY: McGraw-Hill, 2014.

An asymptomatic middle-aged woman is found to have a serum sodium level of 125 mEq/L after routine laparoscopic cholecystectomy. Which of the following is the most appropriate management strategy for this patient?

a. Administration of hypertonic saline solution

b. Administration of normal saline

c. Administration of sodium chloride tablets

d. Restriction of free water

e. Diuresis with furosemide

The answer is d. The initial, and often definitive, management of an asymptomatic patient with hyponatremia is free water restriction. Symptomatic hyponatremia, which occurs at serum sodium levels less than or equal to 120 mEq/L, can result in headache, seizures, coma, and signs of increased intracranial pressure and may require infusion of hypertonic saline. Since this patient is asymptomatic, she ...

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