Low blood potassium is a condition called hypokalemia. Approximately 98 percent of the body's potassium stores are located within cells in what is known as intracellular fluid, or ICF, according to "Harrison's Principles of Internal Medicine." A delicate balance is maintained between the potassium in the ICF and the amount in the extracellular fluid, or ECF. Hypokalemic states are generally conditions in which potassium has been excessively forced into the ICF or is being abnormally excreted in massive amounts.
Normal Potassium Levels
Potassium normally exists in the blood between 3.5 to 5.0 millimoles per liter, or mmol/L, and sometimes higher at 3.7 to 5.2 mmol/L in adults, according to the National Library of Medicine. Hypokalemia occurs when plasma levels drop below 3.5 mmol/L.
"2007 Current Consult Medicine" explains that for each 1 mEq/L decrease in blood potassium below the level of 3.5 to 4 mmol/L, a loss of about 4 to 5 mEq per kilogram occurs.
Potassium and Electrical Conduction
Potassium is a positively-charged ion that is responsible for the relaxation phase of muscles, especially that of the heart. "Rapid Interpretation of EKGs" says the outflow of potassium ions into the ECF leads to relaxation of myocytes, which allows the heart to fill after contraction. In states of hypokalemia, the electrical conduction of the lower chambers of the heart, called the ventricles, becomes unstable. Thus, when potassium levels are low, the ventricles fire spontaneously, causing dangerous arrhythmias. Other EKG abnormalities due to hypokalemia include torsades de pointes and paroxysmal tachycardia.
Causes
The causes of hypokalemia include excessive kidney elimination in the urine, the use of diuretics such as furosemide, abuse of laxatives and enemas, large volume diarrhea, vomiting, magnesium deficiency, profuse sweating, Cushing's syndrome, diabetic ketoacidosis and leukemia. Medications such as amphotericin B and antibiotics also can cause severe depletion in potassium levels.
Signs and Symptoms
According to "Harrison's Principles of Internal Medicine," signs and symptoms vary among patients. Muscle weakness, cramps, constipation, palpitations, fatigue, and increased thirst and urination are common, along with nausea and vomiting.
Signs include muscle paralysis exhibited as a limb paralysis, the breaking down of muscle called rhabdomyolysis, tetany, decreased tendon reflexes, arrhythmias and cardiac arrest.
Treatments
"2007 Current Consult Medicine" indicates that the safest way to treat hypokalemia is by giving oral potassium supplementation. Potassium chloride promotes the most rapid treatment of hypokalemia associated with metabolic acidosis. Only in severe cases of hypokalemia is intravenous potassium applied, due to the possibility of causing rebound hyperkalemia.
References
- "Harrison's Principles of Internal Medicine (17th edition)"; Dr. Anthony Fauci et al, eds.; 2008
- "2007 Current Consult Medicine"; Dr. Maxine Papadakis and Dr. Stephen McPhee; 2007
- "The Johns Hopkins Hospital: The Harriet Lane Handbook (17th edition)"; Dr. Jason Roberston and Dr. Nicole Shilkofski; 2005
- "Step-Up to Medicine (second edition)"; Dr. Steven Agabegi and Dr. Elizabeth Agabegi; 2008
- "Rapid Interpretation of EKGs"; Dr. Dale Dubin; 2000
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