HYPOKALEMIA   48A

A 45-year-old woman presents to the emergency department after 5 days of nausea, vomiting, and diarrhea. She states that she has only been able to drink water occasionally, and her vomiting and diarrhea have been profuse. On review of systems, she complains of fatigue and muscle cramps. Her medical history includes hypertension, for which she takes hydrochlorothiazide (HCTZ). Physical examination reveals symmetric hyporeflexia of the extremities. An electrocardiogram (ECG) reveals broad and flattened T waves with a prominent U waves. Her serum K⁺ is measured at 2.5 mEq/L.

What are the salient features of this patient’s problem? How do you think through her problem?

Salient features: Vomiting and diarrhea causing extrarenal potassium losses; fatigue and muscle cramps; thiazide diuretic use, causing kaliuresis; hyporeflexia on examination; ECG with flattened T waves and U waves; low serum potassium level

How to think through: The patient’s symptom of fatigue can be attributed to her poor oral intake in the setting of acute illness. What factors in her history and physical examination prompt you to consider an electrolyte abnormality? (Protracted vomiting in combination with diarrhea, muscle cramps, and hyporeflexia.) Is the underlying cause of her hypokalemia, intrarenal or extrarenal? (Both, but mainly extrarenal.) What diagnostic test can help differentiate between an intrarenal and extrarenal cause of the potassium loss? (Measurement of urine K⁺ concentration and calculation of the transtubular potassium gradient.) What role does the thiazide diuretic likely play here? (The gastrointestinal [GI] losses are likely the primary cause of the potassium loss, with HCTZ limiting her ability to retain sufficient potassium to compensate. Given the combination of losses, measurement of urine K⁺ and calculation of the transtubular potassium gradient are not necessary.) How should the patient be managed initially? (Oral repletion of potassium, reserving intravenous repletion [which can be dangerous] if the patient does not tolerate oral potassium. Hydration intravenously or orally. Suspension of HCTZ until full recovery.) If her potassium level were to remain low after initial repletion, is there another electrolyte abnormality that should be explored? (Yes. Look for a low serum magnesium level.)

HYPOKALEMIA   48B

What are the essentials of diagnosis and general considerations regarding hypokalemia?

Essentials of Diagnosis

Serum K⁺ is below 3.5 mEq/L (< 3.5 mmol/L).

Severe hypokalemia may induce dangerous arrhythmias and rhabdomyolysis.

Transtubular potassium concentration gradient (TTKG) can distinguish renal from nonrenal loss of potassium.

General Considerations

GI loss from infectious diarrhea is the most common cause.

Potassium shift into the cell is transiently stimulated by insulin and glucose and facilitated by β-adrenergic stimulation; α-adrenergic stimulation blocks potassium shift into the cell.

Aldosterone increases potassium secretion in the distal renal tubule.

Magnesium is a cofactor for potassium uptake and is required for maintenance of potassium levels; magnesium depletion should be suspected in persistent or refractory hypokalemia.

Stay updated, free articles. Join our Telegram channel

Join