A 21-year-old woman comes to the physician with progressive weakness and loss of energy. She nearly collapsed yesterday while performing one of her routine 3-hour workouts. She is not doing well academically in college despite persistent attempts to improve her grades. Her blood pressure is 102/58 mm Hg and pulse is 113/min. Her body mass index is 21 kg/m². Fine hair is noted on her scalp. Examination shows dental erosions with slightly enlarged cheeks. There is no edema. Laboratory results are as follows: In addition to potassium supplementation, which of the following is the best treatment to correct the laboratory abnormalities in this patient?

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11ec25c8_d111_95b8_bc81_33c66403cb81_MD0003_00 This patient's presentation (age, exercise, fine hair, dental erosions) is consistent with likely bulimia nervosa. Bulimia is more common in younger women and leads to binge eating followed by induced vomiting. The body mass index tends to be normal or slightly low. Patients can present with hypotension, tachycardia, dry skin, hair loss, parotid gland hypertrophy with puffy cheeks, and dental erosions due to periodic induced vomiting. The chronic vomiting can lead to volume depletion causing metabolic alkalosis (MA), hypokalemia, and hypochloremia. MA is due to an underlying disorder producing excess bicarbonate (generation phase) combined with a process preventing renal bicarbonate excretion (maintenance phase). MA is further classified as saline responsive or resistant. The generation phase in saline-responsive MA can be due to urinary or gastrointestinal hydrogen loss (eg, diuretics, vomiting) or decreased oral intake. The maintenance phase (eg, hypovolemia) prevents the normal kidney from excreting the excess bicarbonate in the urine. The kidneys perceive a decreased effective arterial blood volume from the underlying etiology (eg, vomiting with volume depletion) and increase renin and aldosterone release. This leads to sodium reabsorption, potassium excretion, and hydrogen excretion. There is also decreased bicarbonate excretion. If the history cannot provide the etiology, urine chloride can differentiate between saline-resistant and saline-responsive MA. Saline-resistant MA has excess mineralocorticoid causing hydrogen and potassium loss and increased sodium retention leading to increased extracellular volume. The kidneys respond by excreting both sodium and chloride to result in high urine chloride. Saline-responsive MA has low urine chloride (<20 mEq/L) due to hypovolemia and hypochloremia. Treatment for both types focuses on the underlying cause to reverse generation and increase renal bicarbonate excretion. In saline-responsive MA, normal saline administration restores arterial volume, corrects hypochloremia, and increases urinary bicarbonate excretion. (Choice A) Acetazolamide is a diuretic that works by inhibiting carbonic anhydrase, which leads to decreased reabsorption of bicarbonate, sodium, and chloride. This may improve her alkalosis somewhat; however, this will worsen her volume depletion. Additionally, acetazolamide causes hypokalemia, an undesirable side effect in this woman who already has a low serum potassium concentration. It can be considered in edematous patients with metabolic alkalosis. (Choices B and D) Hyperventilation decreases pCO₂ and causes respiratory alkalosis. Breathing into a bag increases pCO₂ and decreases pH slightly, but it does not reverse the underlying metabolic alkalosis. (Choices C and E) Calcium gluconate and insulin can be used as acute therapy for hyperkalemia. This patient has hypokalemia. (Choice F) Loop diuretics increase distal sodium delivery and the secretion of aldosterone, which would further worsen metabolic alkalosis, hypokalemia and volume depletion. (Choice H) Sodium bicarbonate infusion would not be needed in a patient who already has excess serum bicarbonate. It is used primarily in those with metabolic acidosis, hyperkalemia, and renal failure. Educational objective: The pathogenesis of metabolic alkalosis requires generating excess bicarbonate (generation phase) and preventing excretion of excess bicarbonate (maintenance phase). Treatment involves addressing the underlying cause and promoting urinary bicarbonate excretion. References: Rational treatment of acid-base disorders. (http://www.ncbi.nlm.nih.gov/pubmed/2196165)

A 21-Year-Old Woman Comes to the Physician with Progressive Weakness