endocrine and metabolic disorders
Hypokalemia
Etiology of Hypokalemia
Hypokalemia can be caused by decreased intake of potassium but is usually caused by excessive losses of potassium in the urine or from the gastrointestinal (GI) tract. Abnormal GI potassium losses occur in all of the following: Chronic diarrhea, including chronic laxative abuse and bowel diversion Clay (bentonite) ingestion, which binds potassium and greatly decreases absorption Rarely, villous adenoma of the colon, which causes massive potassium secretion Protracted vomiting or gastric suction (which removes volume and hydrochloric acid) causes renal potassium losses due to Metabolic Alkalosis 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: After administration ofinsulin Familial Periodic Paralysis None Glycogenesis during total parenteral nutrition or enteral hyperalimentation (stimulatinginsulinrelease) Stimulation of the sympathetic nervous system, particularly with beta 2-agonists (eg,albuterol,terbutaline), which may increase cellular potassium uptake Hyperthyroidism (occasionally) due to excessive beta-sympathetic stimulation (hypokalemic Familial Periodic Paralysis 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: Adrenal steroid excess that is due to Cushing Syndrome , Bartter Syndrome and Gitelman Syndrome , an uncommon genetic disorder that is characterized by renal potassium and sodium wasting, excessive production of renin and aldosterone, and normotension. Bartter syndrome is caused by mutations in a loop diuretic–sensitive ion transport mechanism in the loop of Henle. Bartter Syndrome and Gitelman Syndrome is an uncommon genetic disorder characterized by renal potassium and sodium wasting, excessive production of renin and aldosterone, and normotension. Gitelman syndrome is caused by loss of function mutations in a thiazide-sensitive ion transport mechanism in the distal nephron. Ingestion of substances such as glycyrrhizin (present in natural licorice and used in the manufacture of chewing tobacco), which inhibits the enzyme 11 beta-hydroxysteroid dehydrogenase (11β-HSDH), preventing the conversion ofcortisol, which has some mineralocorticoid activity, tocortisone, which does not, resulting in high circulating concentrations ofcortisoland renal potassium wasting. Liddle Syndrome , a rare autosomal dominant disorder caused by unrestrained sodium reabsorption in the distal nephron due to one of several mutations found in genes encoding for epithelial sodium channel subunits. Inappropriately high reabsorption of sodium results in both severe Renal potassium wasting can also be caused by numerous congenital and acquired renal tubular diseases, such as the Renal Tubular Acidosis and Hypomagnesemia 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 medications that cause hypokalemia. Potassium-wasting diuretics that block sodium reabsorption proximal to the distal nephron include Loop diuretics Osmotic diuretics Thiazide diuretics By inducing diarrhea, laxatives, especially when abused, can cause hypokalemia. Surreptitious use of diuretics or laxatives or both is a frequent cause of persistent hypokalemia, particularly among patients preoccupied with weight loss and among health care professionals with access to prescription medications. Other medications that can cause hypokalemia include Amphotericin B Antipseudomonal penicillins (eg, carbenicillin) Penicillin in high doses Theophylline(both acute and chronic intoxication) 