Hypokalemia definition and meaning
Hypokalemia is defined as a condition when the potassium levels in the blood serum are low, meaning below the normal levels. It is the most common electrolyte disturbance seen in medical practice.
It is also referred to as:
- hypokalemic syndrome
- low potassium syndrome
- hypopotassemia syndrome
Potassium is an essential mineral and an important electrolyte for the functioning of nerve and muscle cells and more importantly of the heart muscle cells. This post on its benefits will tell you how important it can be.
Its levels are controlled by your kidneys, which allow for its excess to be removed from the body through urine. The kidneys excrete 90% of this electrolyte with the remaining excreted by the gastrointestinal system and through sweat.
Mild hypokalemia usually does not show any symptoms. Too low potassium levels can lead to arrhythmia (abnormal heart rhythms) and severe muscle weakness. Severe hypokalemia is life-threatening.
These conditions are reversed once the potassium levels are corrected.
Hypokalemia as defined by serum potassium levels
Normal potassium levels in the blood are between 3.5 and 5.0 mmol/L (3.5 and 5.0 mEq/L).
- Hypokalemia is defined when serum potassium levels fall below 3.5 mEq/L.
- Moderate hypokalemia is a serum level of 2.5-3 mEq/L.
- Severe hypokalemia or a very low potassium level is defined as a level less than 2.5 mEq/L. This is a life-threatening situation and requires urgent medical care.
The total body potassium stores approximately amount to 50 mEq/kg (about 3500 mEq in a 70-kg person). 98% of it is found inside the cells (described as intracellular) of tissues, organs, etc., and only 2% in the blood. 75% of the intracellular potassium is found in the muscle cells.
These numbers are good provided there is no prevailing acid-base abnormality such as diabetic ketoacidosis or severe nonketotic hyperglycemia (NKH).
Secondly, there is no strict correlation between its serum concentration and its total stores in the body.
In chronic hypokalemia, a potassium deficit of 200 to 400 mmol or 200 to 400 mEq in the body stores is required to lower the serum potassium concentration by 1 mmol/L or 1 mEq/L.
Causes of hypokalemia
Often, the cause of hypokalemia can be found through the medical history of the patient.
1. The most common cause of low potassium in the body is due to its loss from the body as a result of severe vomiting, diarrhea, excessive laxative use, or excessive sweating.
2. Sometimes, you could lose potassium through the urine due to the taking of certain drugs such as diuretics or “water pills” (for high blood pressure or heart conditions), which could also drain the excess sodium and water.
3. Again, certain drugs such as insulin, albuterol, and terbutaline cause more potassium to move from the blood into the body cells and this can cause hypokalemia.
4. In adrenal gland disorders, such as Cushing syndrome, the adrenal glands secrete too much aldosterone, which is a hormone that makes the kidneys excrete large amounts of potassium.
5. Sometimes, hypomagnesemia (low magnesium level in blood) can cause low potassium in the blood.
6. Additionally, certain drugs that can cause hypokalemia include:
- beta-adrenergic agonists such as isoproterenol
- alpha-adrenergic antagonists such as clonidine
- antibiotics such as gentamicin and carbenicillin
- antifungal agent amphotericin B can also cause loss of potassium.
- acetaminophen overdose
Since many foods such as beans, dark leafy greens, potatoes, fish, and bananas contain a good amount of this electrolyte, low potassium intake is rarely blamed for hypokalemia.
Mild hypokalemia can often be asymptomatic. The symptoms or the clinical manifestations of severe hypokalemia that may be present are nonspecific and are predominantly seen as related to muscular or cardiac function. Those that are present are often due to the underlying causes rather than due to the hypokalemia itself.
Muscle and nerve symptoms
Mild hypokalemia usually does not cause any symptoms. A larger fall in potassium can cause fatigue, muscle weakness, cramping, twitches, tingling or numbness, and even paralysis.
Moderate to severe falls in potassium levels are known to have an effect on the heart and cause abnormal heart rhythms, which can manifest as a feeling of skipped heartbeats or palpitations.
This can cause you to feel lightheaded or faint. A very low potassium level can even cause your heart to stop.
However, in people who already have a heart problem or take the heart drug digoxin, even a slight fall in potassium can cause these heart effects.
Some people may experience constipation due to the reduced effect of potassium on the smooth muscles of the gastrointestinal tract.
Other symptoms can include:
- Worsening diabetes control or polyuria
- Psychological symptoms (eg, psychosis, delirium, hallucinations, depression)
Potassium deficiency is called hypokalemia. Low levels of the electrolyte can cause certain complications and should be duly addressed.
- On the nerves and muscle front, it will affect your sense of touch and muscle control. There will be tingling and numbness in the extremities. You will feel frequent muscle cramps and muscle twitches. All these problems will disappear once your potassium levels return to normal.
- Fatigue and weakness. Hypokalemia results in poor cellular metabolism resulting in poor energy output by the cells. This can make you feel tired and weak.
- Effects on the heart. Your heart beats normally due to the control of the nerves. Potassium deficiency will alter the heart rhythm and cause arrhythmias (rapid and irregular beating of the heart). This condition requires immediate medical attention.
- Effects on kidneys. Hypokalemia will result in loss of calcium through the kidneys. This can cause kidney stones and calcium deficiency.
- On the digestive front, low potassium can cause weak digestion and constipation, abdominal pain, and bloating. This is due to the improper functioning of the nerves that control the gastrointestinal tract functions.
Tests to diagnose hypokalemia
Low potassium levels are diagnosed by
- measuring its levels in the blood
- through an ECG (electrocardiography)
- through measuring its levels in urine
- a serum magnesium assay
Urine electrolytes (potassium and chloride): Tests for urine electrolytes help to differentiate the renal causes from non-renal causes of hypokalemia when the cause of hypokalemia is not readily known.
If the urine potassium level is less than 20 mEq/L, possible causes could be:
- Diarrhea and regular laxative use
- Diet or total parenteral nutrition (TPN) contents
- The use of insulin, excessive bicarbonate supplements, and episodic weakness
The possible cause could be diuretics if the urine potassium level is higher than 40 mEq/L. If diuretic use is absent, test for arterial blood gases (ABG) and find out the acid-base balance. If alkalosis is found to be present, possible causes could be one of the following:
- Bartter syndrome
- Gitelman syndrome
- Mineralocorticoid excess
Low potassium levels in the blood can be easily measured in the laboratory through a blood test.
The test that is ordered is the basic metabolic panel, which includes testing for serum sodium, potassium, glucose, chloride, bicarbonate, BUN, and creatinine.
Patients with high blood pressure who are on diuretics such as hydrochlorothiazide and furosemide often lose potassium through urine. They are, therefore, regularly monitored by blood tests to verify that their blood level is normal.
Similarly, patients with long-standing diarrhea and vomiting are tested for electrolytes because of loss of water and electrolytes, which can cause dehydration and weakness.
A false hypokalemia reading can occur when blood with a high WBC count is left at room temperature. This happens due to the removal of potassium by the WBCs. Repeating the test for confirmation, therefore, becomes necessary.
ECG changes in hypokalemia
An electrocardiogram (ECG) can also show changes indicating the presence of hypokalemia, characterized by flat “t” waves and/or characteristic “U” waves on the EKG tracing.
Other investigations include:
Arterial blood gas (ABG) analyses are done to detect metabolic acidosis or alkalosis
Testing for serum digoxin level becomes necessary if the patient is on digitalis. People with heart failure are commonly given digoxin and diuretics. Many diuretics can cause potassium loss through urine. Its low level in the body increases the risk of digitalis toxicity.
Management and treatment
The aim of hypokalemia management is
- First, stop the potassium loss
- Replenish its stores
- Find out the cause of hypokalemia and treat it.
- Prevent complications
Oral potassium chloride is the medicine of choice to replenish the lost stores when the person is losing potassium as in when he or she is on thiazide diuretics.
Potassium-sparing diuretics could be an ideal replacement provided kidney function is normal.
To stop its loss due to diuretics, angiotensin-converting enzyme (ACE) inhibitors could be a better alternative to treat hypertension because they inhibit renal potassium excretion.
However, a careful watch should be kept on the potassium levels in patients on ACE inhibitors with renal insufficiency who are taking its supplements or potassium-sparing diuretics.
Potassium can irritate the digestive tract; its supplements should, therefore, be taken in small doses several times a day with food instead of a single large dose.
Indications for treatment with intravenous infusion of potassium to rapidly treat hypokalemia include:
- Dangerously low potassium levels
- Abnormal heart rhythms due to very low levels.
- Oral supplements are ineffective.
- The person continues to lose more potassium than can be replenished by oral supplements.
If hypomagnesemia is present with hypokalemia, it too has to be treated.