Hypokalemia

Abnormal GI potassium losses occur in all of the following:

Protracted vomiting or gastric suction (which removes volume and hydrochloric acid) causes renal potassium losses due to metabolic alkalosis Metabolic Alkalosis Metabolic alkalosis is primary increase in bicarbonate (HCO3⁻) with or without compensatory increase in carbon dioxide partial pressure (Pco2); pH may be high or nearly normal. Common... read more and stimulation of aldosterone due to volume depletion; aldosterone and metabolic alkalosis both cause the kidneys to excrete potassium.

The transcellular shift of potassium into cells may also cause hypokalemia. This shift can occur in any of the following:

Familial periodic paralysis Familial Periodic Paralysis Familial periodic paralysis is a rare autosomal dominant condition with considerable variation in penetrance characterized by episodes of flaccid paralysis with loss of deep tendon reflexes... read more is a rare autosomal dominant disorder characterized by transient episodes of profound hypokalemia thought to be due to sudden abnormal shifts of potassium into cells. Episodes frequently involve varying degrees of paralysis. They are typically precipitated by a large carbohydrate meal or strenuous exercise.

Various disorders can increase renal potassium excretion.

Excess mineralocorticoid (ie, aldosterone) effect can directly increase potassium secretion by the distal nephrons and occurs in any of the following:

Renal potassium wasting can also be caused by numerous congenital and acquired renal tubular diseases, such as the renal tubular acidoses Renal Tubular Acidosis Renal tubular acidosis (RTA) is acidosis and electrolyte disturbances due to impaired renal hydrogen ion excretion (type 1), impaired bicarbonate resorption (type 2), or abnormal aldosterone... read more and Fanconi syndrome Fanconi Syndrome Fanconi syndrome consists of multiple defects in renal proximal tubular reabsorption, causing glucosuria, phosphaturia, generalized aminoaciduria, and bicarbonate wasting. It may be hereditary... read more , an unusual syndrome resulting in renal wasting of potassium, glucose, phosphate, uric acid, and amino acids.

Hypomagnesemia Hypomagnesemia Hypomagnesemia is serum magnesium concentration < 1.8 mg/dL (< 0.70 mmol/L). Causes include inadequate magnesium intake and absorption or increased excretion due to hypercalcemia or drugs... read more is a common correlate of hypokalemia. Much of this correlation is attributable to common causes (ie, diuretics, diarrhea), but hypomagnesemia itself may also result in increased renal potassium losses.

Diuretics are by far the most commonly used drugs that cause hypokalemia. Potassium-wasting diuretics that block sodium reabsorption proximal to the distal nephron include

By inducing diarrhea, laxatives, especially when abused, can cause hypokalemia. Surreptitious diuretic or laxative use or both is a frequent cause of persistent hypokalemia, particularly among patients preoccupied with weight loss and among health care practitioners with access to prescription drugs.

Other drugs that can cause hypokalemia include

ECG should be done on patients with hypokalemia. Cardiac effects of hypokalemia are usually minimal until serum potassium concentrations are < 3 mEq/L (< 3 mmol/L). Hypokalemia causes sagging of the ST segment, depression of the T wave, and elevation of the U wave. With marked hypokalemia, the T wave becomes progressively smaller and the U wave becomes increasingly larger. Sometimes, a flat or positive T wave merges with a positive U wave, which may be confused with QT prolongation (see figure ECG patterns in hypokalemia ECG patterns in hypokalemia ). Hypokalemia may cause premature ventricular beats Ventricular Premature Beats (VPB) Ventricular premature beats (VPB) are single ventricular impulses caused by reentry within the ventricle or abnormal automaticity of ventricular cells. They are extremely common in both healthy... read more and premature atrial contractions Atrial premature beats Various rhythms result from supraventricular foci (usually in the atria). Diagnosis is by electrocardiography. Many are asymptomatic and require no treatment. (See also Overview of Arrhythmias... read more , ventricular Ventricular Tachycardia (VT) Ventricular tachycardia is ≥ 3 consecutive ventricular beats at a rate ≥ 120 beats/minute. Symptoms depend on duration and vary from none to palpitations to hemodynamic collapse and death. Diagnosis... read more and supraventricular tachyarrhythmias Reentrant Supraventricular Tachycardias (SVT) Including Wolff-Parkinson-White Syndrome Reentrant supraventricular tachycardias (SVT) involve reentrant pathways with a component above the bifurcation of the His bundle. Patients have sudden episodes of palpitations that begin and... read more , and 2nd- or 3rd-degree atrioventricular block Atrioventricular Block Atrioventricular (AV) block is partial or complete interruption of impulse transmission from the atria to the ventricles. The most common cause is idiopathic fibrosis and sclerosis of the conduction... read more . Such arrhythmias become more severe with increasingly severe hypokalemia; eventually, ventricular fibrillation may occur. Patients with significant preexisting heart disease and patients receiving digoxin are at risk of cardiac conduction abnormalities as a result of even mild hypokalemia.

The cause of hypokalemia is usually apparent by history (particularly the drug history); when it is not, further investigation is warranted.

After acidosis and other causes of intracellular potassium shift (increased beta-adrenergic effect, hyperinsulinemia) have been eliminated, 24-hour urinary potassium and serum magnesium concentrations are measured. In hypokalemia, potassium secretion is normally < 15 mEq/L (< 15 mmol/L). Extrarenal (GI) potassium loss or decreased potassium ingestion is suspected in chronic unexplained hypokalemia when renal potassium secretion is < 15 mEq/L (< 15 mmol/L). Secretion of > 15 mEq/L (> 15 mmol/L). suggests a renal cause for potassium loss. Unexplained hypokalemia with increased renal potassium secretion and hypertension suggests an aldosterone-secreting tumor or Liddle syndrome. Unexplained hypokalemia with increased renal potassium loss and normal blood pressure suggests Bartter syndrome or Gitelman syndrome, but hypomagnesemia, surreptitious vomiting, and diuretic abuse are more common and should also be considered.