A 20-year-old woman with fatigue and palpitations

INITIAL MANAGEMENT OF HYPOKALEMIA

The initial management of hypokalemia should focus on life-threatening emergencies. While patients with potassium levels greater than 3 mmol/L are usually asymptomatic, those with levels below 3 mmol/L present with muscle weakness and rhabdomyolysis.⁴ An acute drop in serum potassium to less than 2 mmol/L is associated with respiratory muscle weakness and ventricular arrhythmias.⁴ If the patient has cardiac symptoms or hypoventilation due to respiratory muscle weakness, continuous monitoring in the intensive care unit and aggressive therapy are warranted.

4. Which potassium formulation is most appropriate for the treatment of hypokalemia in this patient?

• Potassium chloride
• Potassium phosphate
• Potassium acetate

Oral potassium is preferable in patients with a serum potassium above 2.5 mmol/L.^4,11 Potassium phosphate should be used when supplementation with both potassium and phosphorus is needed. Potassium acetate should be reserved for patients with acidosis and hypokalemia. Otherwise, potassium chloride is typically preferred.^4,12 It comes in liquid and tablet forms. Liquid forms have an unpleasant taste, whereas tablets are usually well tolerated. No more than 20 to 40 mEq of potassium chloride tablets should be given at a time, since higher doses are associated with gastrointestinal mucosal injury.¹²

Potassium chloride is particularly preferred in patients with metabolic alkalosis, since increased chloride intake and delivery to the distal tubule increases the expression of pendrin, a luminal chloride and bicarbonate exchanger in the cortical collecting duct.¹³ With metabolic alkalosis, increased excretion of bicarbonate occurs through up-regulation of pendrin. Potassium depletion down-regulates pendrin.¹³ Additionally, correction of metabolic alkalosis increases serum potassium by movement of potassium from the intracellular to the extracellular space.

Intravenous potassium should be reserved for patients with severe hypokalemia (< 2.5 mmol/L) or significant arrhythmias.¹¹ Oral and intravenous potassium can safely be given simultaneously.¹¹ The intravenous rate should not exceed more than 10 to 20 mEq of potassium chloride per hour unless the patient has a life-threatening arrhythmia, respiratory failure, or severe hypokalemia.^14,15 In life-threatening situations, a femoral line should be placed, and potassium should be given as rapidly as 20 mEq over 15 to 20 minutes.¹⁴ Cannulation of the subclavian and internal jugular veins should be avoided in severe hypokalemia since mechanical irritation from guidewire placement can provoke ventricular arrhythmias.¹⁴

During intravenous administration of potassium, laboratory monitoring after every 20 mEq of potassium chloride is advised because of the possibility of rebound hyperkalemia. In patients with severe hypokalemia, avoidance of factors that can worsen intracellular shift of potassium is also important. Avoid dextrose-containing fluids to prevent insulin-induced shifting of potassium into cells. Restore intravascular volume to blunt hypovolemia-induced renin and aldosterone secretion. If a patient presents with severe hypokalemia and acidosis, correct the hypokalemia before the acidosis to avoid intracellular shift of potassium.

OUR PATIENT’S MANAGEMENT AND FOLLOW-UP PLAN

Given the severity of our patient’s hypokalemia and her complaint of palpitations, she was admitted to the hospital for monitoring. She required 180 mEq of intravenous potassium chloride and 140 mEq of oral potassium chloride during the first 24 hours in order to achieve a serum potassium level above 3 mmol/L. Electrocardiographic U waves resolved once the level was above 2 mmol/L, and ST depressions resolved once it was above 3 mmol/L. The QT interval normalized after 24 hours of hospitalization.

On discharge, she was prescribed oral potassium chloride 40 mEq daily and magnesium sulfate 400 mg twice daily, with plans for a followup visit with her outpatient therapy team, which includes a psychiatrist, a social worker, and her primary care provider. She declined a referral for inpatient therapy but agreed to a goal of decreasing the frequency of induced vomiting and outpatient visits. She was also educated on how and when to access emergency medical care.¹⁶