Diseases

Potassium is critical for the normal functioning of the muscles, heart, and nerves. It plays an important role in controlling activity of smooth muscle (such as the muscle found in the digestive tract) and skeletal muscle (muscles of the extremities and torso), as well as the muscles of the heart. It is also important for normal transmission of electrical signals throughout the nervous system within the body.Normal blood levels of potassium are critical for maintaining normal heart electrical rhythm. Both low blood potassium levels (hypokalemia) and high blood potassium levels (hyperkalemia) can lead to abnormal heart rhythms.The most important clinical effect of hyperkalemia is related to electrical rhythm of the heart. While mild hyperkalemia probably has a limited effect on the heart, moderate hyperkalemia can produce EKG changes (EKG is a reading of the electrical activity of the heart muscles), and severe hyperkalemia can cause suppression of electrical activity of the heart and can cause the heart to stop beating.Another important effect of hyperkalemia is interference with functioning of the skeletal muscles. Hyperkalemic periodic paralysis is a rare inherited disorder in which patients can develop sudden onset of hyperkalemia, which in turn causes muscle paralysis. The reason for the muscle paralysis is not clearly understood, but it is probably due to hyperkalemia suppressing the electrical activity of the muscle.

Blood is withdrawn from a vein (like other blood tests). The potassium concentration of the blood is determined in the laboratory. If hyperkalemia is suspected, an electrocardiogram (ECG or EKG) is often performed, since the ECG may show changes typical for hyperkalemia in moderate to severe cases. The ECG will also be able to identify cardiac arrhythmias that result from hyperkalemia.

Treatment of hyperkalemia must be individualized based upon the underlying cause of the hyperkalemia, the severity of symptoms or appearance of ECG changes, and the overall health status of the patient. Mild hyperkalemia is usually treated without hospitalization especially if the patient is otherwise healthy, the ECG is normal, and there are no other associated conditions such as acidosis and worsening kidney function. Emergency treatment is necessary if hyperkalemia is severe and has caused changes in the ECG. Severe hyperkalemia is best treated in the hospital, oftentimes in the intensive care unit, under continuous heart rhythm monitoring.Treatment of hyperkalemia may include any of the following measures, either singly or in combination:

• A diet low in potassium (for mild cases).
• Discontinue medications that increase blood potassium levels.
• Intravenous administration of glucose and insulin, which promotes movement of potassium from the extracellular space back into the cells.
• Intravenous calcium to temporarily protect the heart and muscles from the effects of hyperkalemia.
• Sodium bicarbonate administration to counteract acidosis and to promote movement of potassium from the extracellular space back into the cells.
• Diuretic administration to decrease the total potassium stores through increasing potassium excretion in the urine. It is important to note that most diuretics increase kidney excretion of potassium. Only the potassium-sparing diuretics mentioned above decrease kidney excretion of potassium.
• Medications that stimulate beta-2 adrenergic receptors, such as albuterol and epinephrine, have also been used to drive potassium back into cells.
• Medications known as cation-exchange resins, which bind potassium and lead to its excretion via the gastrointestinal tract.
• Dialysis, particularly if other measures have failed or if renal failure is present.

Treatment of hyperkalemia also includes treatment of any underlying causes (for example, kidney disease, adrenal disease, tissue destruction) of hyperkalemia.

Hyperkalemia can be asymptomatic, meaning that it causes no symptoms. Sometimes, patients with hyperkalemia report vague symptoms including:

• nausea,
• fatigue,
• muscle weakness, or
• tingling sensations.

More serious symptoms of hyperkalemia include slow heartbeat and weak pulse. Severe hyperkalemia can result in fatal cardiac standstill (heart stoppage). Generally, a slowly rising potassium level (such as with chronic kidney failure) is better tolerated than an abrupt rise in potassium levels. Unless the rise in potassium has been very rapid, symptoms of hyperkalemia are usually not apparent until potassium levels are very high (typically 7.0 mEq/l or higher).Symptoms may also be present that reflect the underlying medical conditions that are causing the hyperkalemia.

The major causes of hyperkalemia are kidney dysfunction, diseases of the adrenal gland, potassium sifting out of cells into the blood circulation, and medications.

Hyperkalemia is a common diagnosis. Fortunately, most patients who are diagnosed have mild hyperkalemia (which is usually well tolerated). However, any condition causing even mild hyperkalemia should be treated to prevent progression into more severe hyperkalemia. Extremely high levels of potassium in the blood (severe hyperkalemia) can lead to cardiac arrest and death. When not recognized and treated properly, severe hyperkalemia results in a high mortality rate.Technically, hyperkalemia means an abnormally elevated level of potassium in the blood. The normal potassium level in the blood is 3.5-5.0 milliequivalents per liter (mEq/L). Potassium levels between 5.1 mEq/L to 6.0 mEq/L reflect mild hyperkalemia. Potassium levels of 6.1 mEq/L to 7.0 mEq/L are moderate hyperkalemia, and levels above 7 mEq/L are severe hyperkalemia.