Electrolytes Explained

Electrolytes

The important learning points for electrolytes include:

• Sodium, potassium, calcium, magnesium, phosphorus, and chloride
• The normal values clinicians must know for each electrolyte
• The major contributors to electrolyte imbalance
• Unique signs and symptoms of electrolyte imbalance

The basic metabolic panel is a blood test that measures electrolytes, glucose, and kidney function.

Sodium

Sodium is involved with nerve impulses. Sodium’s abbreviation starts with an “N” —an easy mnemonic is “N” for nerves. 

A standard sodium value range is 135 to 145 mEq/L, though it varies between institutions.

Sodium is an essential electrolyte because it is essential for nerve impulses.

Primary Functions

Sodium’s main function is the conduction of nerve impulses.

It is also a major contributor to serum osmolality — the concentration of particles within fluid. The three major contributors to serum osmolality are sodium, protein, and glucose. The more in the patient’s fluid, the more elevated the serum osmolality.

Hyponatremia

Hyponatremia is a sodium level below 135 mEq/L. The main contributor to hyponatremia is fluid volume excess, also called hemodilution. 

Congestive heart failure and kidney failure may cause hemodilution. Syndrome of inappropriate antidiuretic hormone (SIADH) is when the body secretes too much antidiuretic hormone and is another hyponatremia contributor.

Fluid volume excess causes low sodium levels on the basic metabolic panel (BMP), adversely affecting the nervous system. Clinical manifestations include muscle cramps and weakness. Clinicians must watch for seizures due to the diluted sodium levels.

When the patient’s sodium is diluted, serum osmolality drops. The osmolality inside the cells becomes higher than the osmolality in the vascular space. The fluid transports to the places of higher concentration, leaving the vascular space and entering the cell. This may lead to cerebral swelling, cerebral edema, and seizures.

Hypernatremia

Hypernatremia is a high sodium level over 145 mEq/L. Fluid volume deficit causes hemoconcentration, the main contributor of hypernatremia. Hypernatremic patients often are often dehydrated and regularly vomiting. Their sodium levels on the BMP are incredibly elevated.

Potassium

The normal potassium range is 3.5 to 5.0 mEq/L, however it varies across institutions. Around 98% of potassium is inside the cells due to the sodium-potassium pump. Sodium is mainly outside the cells.

The sodium-potassium pump brings potassium into the cell.

Primary Functions

Potassium is essential for:

• Cardiac function
• Nerve conduction
• Muscle contraction

Read: Electrocardiogram Interpretation in 10 Simple Steps

Hypokalemia

Hypokalemia is a low serum potassium less than 3.5 mEq/L, and one of its main causes is loop diuretics such as furosemide (Lasix^®).

Insulin is another cause. It stimulates the sodium-potassium pump and shifts potassium into the cells. 

Inhaled albuterol also pushes potassium into the cells. Treating a COPD patient with breathing treatments and nebulizer treatments with albuterol may decrease potassium.

Hemodilution does not contribute to low potassium levels because potassium lives inside of the cells. Hemodilution contributes to low sodium but not low potassium.

Hyperkalemia

Hyperkalemia is a potassium level over 5.0 mEq/L. It clinically manifests as an arrhythmia with peaked t-waves.

A major contributor to hyperkalemia is renal failure. Renal failure patients are not able to filter potassium out through the kidneys, so it builds up in the body. Other causes of hyperkalemia are ACE-inhibitors and angiotensin II receptor blockers, rhabdomyolysis, hemolysis, and metabolic acidosis.

Related Video – Hs and Ts – Hypo-Hyper Kalemia

Calcium

The normal value for calcium is 8.6 to 10.3 mg/dL, however the range varies.

Primary Functions

Calcium has several important bodily functions:

• Bone metabolism: 99% of calcium is in bones and teeth.
• Blood coagulation: Calcium has a major role in the formation of prothrombin.
• Muscle contraction.

Hypocalcemia

Hypocalcemia is a low calcium level. The hallmark sign of hypocalcemia is tetany, repetitive muscle contractions. Other symptoms include muscle cramps, weakness, and hypotension.

Renal failure is the main contributor to hypocalcemia. The kidneys play a large role in vitamin D synthesis, and the body requires vitamin D to absorb calcium. If the kidneys are not properly synthesizing vitamin D, the body cannot absorb calcium and hypocalcemia presents. 

Calcium levels also decrease in renal failure due to phosphorus build-up. Phosphorus levels increase as calcium levels decrease.

Hypercalcemia

Hypercalcemia is a high calcium level. The main signs are bone pain, kidney stones, abdominal pain, and confusion.

The main contributor to hypercalcemia is hyperparathyroidism. The parathyroid glands secrete parathyroid hormone (PTH), increasing calcium levels. If a patient has overactive parathyroid glands, calcium levels elevate.

The parathyroid glands secrete parathyroid hormone (PTH) to increase serum calcium levels.

Magnesium

The normal value for magnesium is 1.7 to 2.2 mg/dL, though it varies. Magnesium resides mostly in the bone and intracellular fluid and is primarily eliminated via the kidneys.

Primary Functions

Magnesium is important because it:

• Maintains cardiac rhythm
• Acts at neuromuscular junctions to facilitate nerve impulses

Magnesium plays a major role in cardiac rhythm. If a patient enters into a dysrhythmia, the provider first checks the potassium level. If the potassium level is stable, clinicians next look at the magnesium level.

Hypomagnesemia

Hypomagnesemia is a low magnesium level. Patients are often asymptomatic in mild cases. The main contributor to hypomagnesemia is alcoholism. Other causes are diarrhea and decreased absorption in the gastrointestinal tract.

Hypermagnesemia

Hypermagnesemia is a high magnesium level. The main symptoms are lethargy, weakness, and arrhythmias. The main contributor is renal failure. Since magnesium is primarily eliminated by the kidneys, patients with renal failure are not able to get rid of magnesium, so it builds up in the body.

Related Video – Magnesium: ACLS Medications

Phosphorus

The normal phosphorus range is 2.5 to 4.5 mg/dL. When phosphorus is a charged ion, it’s known as phosphate. The majority of phosphate is contained in the bones.

Primary Functions

The main functions of phosphorus are:

• Cellular metabolism: Phosphorus helps produce adenosine triphosphate (ATP).
• Formation of bone.
• Components of phospholipids and nucleic acids.

Phosphate is part of the adenosine triphosphate (ATP) molecule. The phosphate molecules are on the left side of the image.

Hypophosphatemia

Hypophosphatemia is a phosphorus level below 2.5 mg/dL. Patients are usually asymptomatic with mild to moderate hypophosphatemia. Patients with severe hypophosphatemia are weak due to ATP depletion. 

The main contributors are malabsorption, diarrhea, and antacids. For example, a patient with malabsorption may have a partially removed intestine due to gastric bypass surgery. They can’t effectively absorb nutrients. For antacids, many aluminum and magnesium-based antacids bind to phosphate.

Clinicians must remember if calcium levels increase, phosphorus levels decrease.

Hyperphosphatemia

Hyperphosphatemia is a high phosphorus level over 4.5 mg/dL. The main symptoms are calcium-phosphate precipitation in the joints, skin, heart, lungs. Some patients may develop hypocalcemia and subsequent tetany. 

The main contributor is renal failure. The kidneys normally excrete phosphate. As kidney function worsens, so does its ability to excrete phosphate. Patients cannot properly filter out phosphorus.

As kidney function decreases, so does the ability to filter and eliminate various electrolytes in the body, especially phosphorus and calcium.

Chloride

Chloride is an often forgotten yet important electrolyte. A normal chloride level is between 95 to 105 mmol/L.

Primary Functions

Chloride’s main functions are:

• Acid-base balance: Chloride is part of hydrochloric acid, contributing to acidity in the body.
• Fluid balance.

Chloride and sodium have a complementary relationship. Sodium (Na⁺) has a positive charge, while chloride (CI^–) has a negative charge, so they’re attracted to each other. They each have an equal role in fluid balance.

Hypochloremia

Hypochloremia is a low chloride level. Its main contributors are prolonged vomiting, diarrhea, and alkalosis.

Hyperchloremia

Hyperchloremia is a high chloride level. Its main contributors are hypernatremia, vomiting, and severe dehydration. Vomiting and severe dehydration lead to a state of hemoconcentration, causing elevated sodium and chloride levels.

Summary

The six important electrolytes within the body are sodium, potassium, calcium, magnesium, phosphorus, and chloride. There are standard ranges for each, and an elevated or decreased level will cause a variety of symptoms.