The ratio of intracellular to extracellular potassium is important in determining the cellular membrane potential. Small changes in the extracellular potassium level can have profound effects on the function of the cardiovascular and neuromuscular systems.
Low potassium (hypokalemia) refers to a lower than normal level of potassium in your bloodstream. Potassium is a chemical (electrolyte) that is critical to the proper functioning of nerve and muscles cells, particularly heart muscle cells. Hypokalemia is generally defined as a serum potassium level of less than 3.5 mEq/L (3.5 mmol/L). Severe hypokalemia is a level of less than 2.5 mEq/L.
Most cases of hypokalemia occur in the setting of specific disease states, and most common cause of low potassium is excessive potassium loss in urine or from the digestive tract, transcellular shift (movement of potassium from serum into cells), or the direct effect of medications. Only rarely is low potassium due to sweating or not getting enough potassium in your diet.
Patients are often asymptomatic, particularly those with mild hypokalemia. Symptoms that are present are often from the underlying cause of the hypokalemia rather than the hypokalemia itself. The symptoms of hypokalemia are nonspecific and predominantly are related to muscular or cardiac function.
Those symptoms include: weakness and fatigue (most common), palpitations, psychological symptoms (eg, psychosis, delirium, hallucinations, depression). Muscle cramps and pain are only present in severe cases, as Troponin's (a regulatory protein complex that is integral to muscle contraction in skeletal and cardiac muscle) becomes impaired. Therefore, hypokalemia can hyperpolarize skeletal muscle cells, impairing their ability to develop the depolarization necessary for muscle contraction. It can also reduce blood flow to skeletal muscles. The reduced blood flow can predispose patients to Rhabdomyolysis (damaged skeletal muscle tissue breaks down its breakdown products are released into the bloodstream) especially when vigorous exercise is combined with impaired blood-flow regulation. The combination of these effects frequently leads to muscle weakness, easy fatigability, cramping, and myalgias. Paralysis, although uncommon, can occur in cases of profound potassium deficiency.
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