Potassium is one of the electrolytes that allows for cells to maintain their membrane potential or ability to discharge. Smooth and skeletal muscles and nerves are particularly affected when potassium levels fall. Inadequate potassium in the blood, or hypokalemia, disturbs electrical function of cells by affecting their ability to depolarize, or discharge, and repolarize, or recharge.
Causes of Hypokalemia
Hypokalemia may result when stores of potassium in the body are adequate, but the balance is off. This is often due to a shift of potassium when it is moved into the cells from the extracellular environment in response to high insulin or circulating stress hormones. Low blood potassium may also be the result of a dietary deficiency, kidney losses or gastrointestinal losses due to diarrhea, vomiting, or malabsorption.
People with high blood pressure are often prescribed diuretics, which work on the collecting ducts of the kidney to excrete sodium and water. This excretion leads to the activation of the renin-angiotensin-aldosterone system, which responds to decreased volume and acts on the kidneys to conserve sodium and water if the a person becomes hypovolemic from excess diuresis. When sodium is conserved, potassium excretion is enhanced, leading to lowered levels.
Symptoms of Hypokalemia
Normal serum potassium ranges from 3.5 to 5 millimoles per liter. When potassium levels are below this range, cells cannot recharge after discharge and are unable to fire repeatedly, which leads to the disturbance of electrical signaling between cells. This disturbance results in muscle weakness, muscles aches and cramps and cardiac palpitations. A small drop in potassium may not necessarily cause symptoms, but large drops can be life-threatening. More serious symptoms of severe hypokalemia result from a disturbance of electrical activity within the conducting cells. These include abnormal heart rhythms, constipation, fatigue, muscle damage or rhabodmyolysis, muscle spasms and even periodic paralysis.
Treatment of Hypokalemia
Serum potassium levels above 3 millimoles per liter can be treated with oral potassium replacement if symptoms occur. However, serum levels under 3 millimoles per liter may require intravenous replacement, as very low levels can quickly become life-threatening. When potassium is given intravenously, it must be infused at a slow rate, as potassium is irritating to the veins and infusing it too quickly can result in cardiac dysrhythmia.
Bananas, whether in raw or smoothie form, are a great source of potassium. Meat lovers can reach for fish, such as salmon, cod or flounder, beef or turkey. Other fruits and vegetables with high levels of potassium include cantaloupe, oranges, strawberries, kiwi, avocados, apricots, mushrooms, peas, beets and tomatoes.
- UpToDate: Clinical Manifestations and Treatment of Hypokalemia
- Seminars in Neurology: Potassium Disorders
- Harrison's Principles of Internal Medicine, 18th edition; AS Fauci et al.
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