Hypokalemia – Diagnosis and Treatment

The normal potassium level in the human blood is between 3.5-5.0 mEq/L. Hypokalemia is characterized by potassium levels that are lower than 3.5 mEq/L and it can be problematic particularly due to the neuromuscular and cardiovascular complications it may cause. It may be classified as mild (3-3.4 mEq/L), moderate (2.5-2.9mEq/L) or severe (<2.5 mEq/L).

In normal situations, the daily potassium intake is around 40-120 mEq/day, with most of it being excreted However, the kidneys have the capacity to reduce to excretion to only 5-25mEq/day if needed, and for that reason low dietary ingestion is almost never an isolated cause of hypokalemia (although it may very well make it worse).

The causes, clinical manifestations and treatment of hypokalemia are discussed below.

CAUSES:

Hypokalemia can be caused by one or a combination of the situations below:

Increased potassium loss:

Drugs: diuretics (thiazides, loop diuretics), laxatives, glucocorticoids, fludrocortisone, penicillin, amphotericin, aminoglycosides
GI losses: diarrhea, vomiting, ileostomy, intestinal fistula
Renal causes (renal tubular acidosis, diuretics, increased mineralocorticoid activity, polyuria, Bartter and Gitelman syndromes), dialysis
Endocrine disorders: hyperaldosteronism (Conn’s syndrome), Cushing’s syndrome

Trans-cellular shift / Cellular uptake:

Insulin/glucose therapy
Increase on the beta-adrenergic activity (e.g. use of salbutamol and other beta-agonists, theophylline, head injury)
Metabolic alkalosis
Hypothermia
Increased blood cell production
Some intoxications (barium, cesium, chloroquine)

Decreased potassium intake (not a major contributor)

Increased sweat losses (not usually a major contributor)

Magnesium depletion (associated with increased renal potassium loss)

SIGNS & SYMPTOMS:

It may be asymptomatic or present with one or more of the signs and symptoms mentioned below. The severity of the symptoms depends not only on the potassium levels, but also on how quick the potassium levels dropped from the patient`s baseline. The presentation may include:

Weakness
Constipation
Muscle cramps
Respiratory difficulties
ECG changes (U waves, T wave flattening, ST segment depression)
Cardiac arrhythmias (premature atrial and ventricular beats, sinus bradycardia, paroxysmal atrial or junctional tachycardia, atrioventricular block, and ventricular tachycardia or fibrillation)
Rhabdomyolysis (severe hypokalaemia)
Ascending paralysis (severe hypokalaemia)

DIAGNOSIS:

The history is often enough to establish the cause of hypokalemia (e.g. a patient that uses diuretics). However in some situations the cause may not be clear. In such cases, measuring the urinary potassium (24h is better) may be helpful to differentiate between urinary loss vs transcellular shift. The presence of hypokalemia and urinary potassium higher than 30mEq/day indicates an inability of the kidneys to concentrate the potassium (and hence indicates that the hypokalemia is caused or worsened by a kidney dysfunction). Another test that can be used is the potassium-to-creatinine ratio, that is <13meq/g creatinine (1.5mEq/mmol creatinine) when the hypokalemia is due to cellular shifts or GI losses and >13meq/g creatinine when the hypokalemia is caused by renal loss. After assessing the urinary potassium, the acid-base status should be evaluated. The interpretation can be as below:

High urinary potassium excretion + Metabolic acidosis: DKA, renal tubular acidosis (type 1 or type 2).
High urinary potassium excretion + Metabolic alkalosis: Diuretics, vomiting, renovascular disease, primary hyperaldosteronism, Gitelman or Bartter syndrome.
Low urinary potassium excretion + Metabolic acidosis: Losses through the lower GI tract (e.g. adenoma, some laxatives).
Low urinary potassium excretion + Metabolic alkalosis: Vomiting (e.g. bulimia), some laxatives.

TREATMENT:

The management of hypokalemia should be focused on preventing or treating the acute complications of low potassium levels, replacing the potassium deficit and treating the underlying cause and preventing further wasting if possible.

For mild asymptomatic hypokalemia potassium supplements should be used (10 to 20 mEq orally, two to four times a day, with meals). If potassium supplements are not enough, potassium sparing diuretics may be used as well, with careful monitoring of serum potassium.

Severe or symptomatic hypokalemia can be treated promptly with oral and IV potassium. The oral potassium should be used in the dose 20-40 mEq three to four times a day (the lower dose is for patients receiving IV potassium, and the higher doses for patients receiving just the oral). The IV potassium can be given in a solution with normal saline (not glucose) in a concentration of 20-60 mEq/L and a rate around 10-20 mEq/h to avoid phlebitis and hyperkalemia (a central vein is a better option for a rate higher than 10 mEq/h). The potassium should be measured again after 40mEq of IV potassium (and further doses will depend on the results). Continuous EEG monitoring should be provided during the treatment. Once the hypokalemia is no longer severe, the IV should be reduced or stopped (continuing only with the oral therapy).

As a general rule, 10mEq of potassium given may increase serum potassium by 0.1.

Potassium chloride is the preferred agent in most situations (except in patients with acidosis which may benefit from potassium bicarbonate).

Low magnesium may occur together with hypokalemia and can make the treatment of the latter harder. In such patients, magnesium replacement should be provided as well.

Dosing forms:
Potassium chloride:
Extended release capsules: KLOR-CON SPRINKLE, MICRO-K or generic – 8 or 10mEq capsules.
Extended release tablets: K-TAB (8, 10 or 20mEq tablets), KLOR-CON or generic (8, 10, or 20 mEq tablets)
Solution PO: K-SOL 20 or 40mEq/15mL (10 or 20%); generic 20 mEq/15mL (10%).

REFERENCES & FURTHER READING: