Fluid and Electrolyte Balance

Fluid and Electrolyte Balance Video

Welcome to this video tutorial on fluid and electrolyte balance!

Fluid and electrolyte balance is essential to the process of life, and abnormal concentrations can be life-threatening. In this video, we will look at how fluid and electrolyte disturbances occur, the simplified function of the electrolyte, normal values, signs and symptoms, and basic treatment.



The body is largely made up of water, or fluids, in fact, it is approximately 50-60% of the body’s weight. Water has many important functions, including maintenance of blood volume; cellular transport of vital substances, such as oxygen and glucose; transport of waste products to the lungs and kidneys for removal; lubrication and cushioning; breakdown of food in the digestive system; a medium for chemical reactions in cells; and maintenance of body temperature.

Intracellular and Extracellular Fluid

Body fluid is further broken down into \(\frac{2}{3}\) intracellular fluid (fluid inside the cell) and \(\frac{1}{3}\) extracellular fluid (fluid outside the cell). All body fluid compartments contain fluids and electrolytes. Cells maintain a balance by the transferring of fluid and electrolytes in and out of the cell. The concentration of electrolytes depends on the fluid volume and the body’s ability to regulate the fluid and solvents. The major intracellular electrolytes are potassium and magnesium. The major extracellular electrolytes are sodium and chloride.


Electrolytes are ions that carry either a positive or negative charge. Exact concentrations of electrolytes are vital to body pH and overall homeostasis. These electrically charged ions move fluids within the body, produce energy, contract muscles, and perform many other roles in the body. The most prominent cations (positively charged ions) are hydrogen, sodium, potassium, magnesium, and calcium. The anions (negatively charged ions) are chloride, bicarbonate, sulfate, and phosphate.

Most of these electrolytes come from our food and fluid intake. Electrolytes can also be affected by medications, hyperalimentation, blood administration, and IV fluids.

Fluid and electrolyte imbalances can occur due to various causes, such as nausea/vomiting, dehydration, surgery, trauma, burn injuries, bleeding, and liver or kidney problems. The body’s electrolytes are regulated by the endocrine system, the vascular system, the gastrointestinal system, and the kidneys.

Electrolyte Reference Values

It’s important to know the normal ranges of the major electrolytes, their basic functions, and the signs and symptoms of imbalances. So let’s start by looking at the reference values you need to memorize—remember that these lab values are a measurement of what is in the ECF (extracellular fluid), it doesn’t measure the total body fluid. Also, these are guidelines, and each lab may have a slight variation, but will also provide reference values with the test result. This list is in order from smallest to largest, showing that the smallest quantity of electrolyte in the ECF is magnesium, compared to sodium, which has the largest amount.

Magnesium is 1.5-2.5 (it’s measured in mEq/L, but don’t be overly concerned about remembering that—it’s the number values that you want to memorize)
Phosphorus is 2.5-4.5
Potassium is 3.5-5.0
Calcium 8.5-10.5
Chloride 95-105

Sodium is 135-145


Let’s look at each one in bold individually, focusing on their basic function in the body, along with the signs and symptoms you will see.


Magnesium is a major intracellular cation (meaning that magnesium is mostly inside the cell and just a small amount in the ECF). Its normal range is 1.5-2.5 mEq/L. The basic function of magnesium is muscle relaxation. So if you have a lot of magnesium, over 2.5 (called hypermagnesemia), then the muscles are too relaxed, causing muscle weakness, vasodilation, hypotension, decreased DTR (deep tendon reflexes), respiratory arrest, and cardiac arrest.

On the other hand, if magnesium is low (called hypomagnesemia), below 1.5, the effect is opposite—muscles are excited, there’s neuromuscular irritability, tremors, increased DTRs, tachycardia, confusion, and seizures. You often see magnesium given in preterm labor or preeclampsia to relax the contractions or decrease the blood pressure. You would need to assess the DTR’s during magnesium administration, because if the magnesium level gets too high, the DTR’s will become faint and diminish, which is a precursor to respiratory depression and cardiac arrest.


Potassium is also a major intracellular cation in the body. Therefore, since the serum electrolyte value is a measurement of the amount of potassium in the ECF, very small variances in the potassium level make a big difference in the patient. Remember, normal level is 3.5-5.0 mEq/L. The basic function of potassium is intracellular excitation, which means it is crucial to heart function, and can cause arrhythmias if the levels are too high or too low. Potassium also plays a role in the conduction of nerve impulses and skeletal muscle activity.


Hyperkalemia is when the potassium level is greater than 5.0 mEq/L, and can be life-threatening. With a lot of potassium, there is an overexcitement of cardiac tissue, and on the ECG you will see tall peaked T waves. You will also see muscle twitching and cramps early on, then later, muscle weakness and paralysis, with possible life-threatening cardiac dysrhythmias. Hyperkalemia is often associated with renal disease because the patient is not excreting out potassium properly, but it can also be a result of using salt substitutes and medications, such as potassium-sparing diuretics. Treatment involves renal dialysis, potassium lowering medications, and restricting potassium-containing foods.


Hypokalemia is when serum potassium falls below 3.5 mEq/L. It is usually a result of bodily fluid losses occurring from vomiting, diarrhea, or sweating; as well as some medications such as diuretics, laxatives, or steroids. Because potassium affects the way neuromuscular cells depolarize and repolarize energy, when potassium levels are low, the cells cannot repolarize, are unable to fire repeatedly, causing muscles and nerves to not function normally. Moderate hypokalemia results in muscle weakness or spasms, leg cramping, numbness/tingling, fatigue, lightheadedness, heart palpitations, bradycardia, and in severe cases, cardiac arrest.

The ECG changes seen with hypokalemia include a flattened T wave and possible extra U wave, because of the repolarization abnormalities. Treatment of the underlying cause and supplemental potassium is usually given. Potassium is found in foods such as bananas, melons, or raw spinach. Also, oral potassium supplements, IV fluids with potassium, and switching to potassium-sparing diuretics will help increase the potassium levels. Be sure IV potassium is diluted and administered with an IV pump because potassium can burn the vein and an overdose can cause cardiac arrhythmias and death.


Calcium is found primarily in the bones and teeth (actually 99%), with the remaining 1% dissolved in the blood. The normal range for the total serum calcium is 8.5-10.5 mg/dL, and about half of that is bound to plasma proteins, mainly albumin, and the other half is ionized or free-floating. Since albumin is made in the liver, someone with liver problems or decreased albumin will show a low serum calcium without symptoms, because the decrease is in the protein-bound rather than the ionized calcium. Patients who have lost ionized calcium will be symptomatic.

So let’s look at the simplified body function of calcium.

Body Function of Calcium

Neuronal excitability (or motor neurons sending signals to muscles, causing them to contract). It’s a little confusing, because hypercalcemia causes decreased muscle contraction, whereas hypocalcemia causes excess muscle contraction and spasms. Think of it as a way to stabilize membrane channels.

In hypocalcemia, there are a lot of easily excitable muscles, but calcium is not there to stabilize the membrane channels. Not enough calcium causes tetany (involuntary contraction of muscles), vomiting and diarrhea (GI muscles are going crazy), convulsions, and heart dysrhythmias. There are 2 classic signs of tetany that are important to know. First is Trousseau’s sign, where you inflate a blood pressure cuff above systolic BP on the arm for 2 minutes, and the hand develops a contracted position. The other is Chvostek’s sign, which is elicited by tapping the patient’s face lightly over the facial nerve, just below the temple, and the result is facial muscle twitching. Treatment for hypocalcemia involves a high-calcium diet, calcium supplements with vitamin D to enhance absorption; or for the more severe cases with signs of tetany, an IV solution of calcium gluconate is given, along with continuous cardiac monitoring.

In hypercalcemia, there is too much calcium, over 10.5 mg/dL. With the excess calcium stabilizing the membrane channels, you will see decreased muscle contraction, constipation from decreased GI tract motility, decreased DTR’s, lethargy, bone pain, and decreased activity of the cardiovascular system, resulting in dysrhythmias and cardiac arrest. Treatment involves hydrating with fluids, cardiac monitoring, and loop diuretics to promote calcium excretion.

Sodium is the major extracellular fluid cation, so its simplified body function is extracellular excitation. It has a big impact on the body’s fluid balance and the functioning of muscles and the central nervous system. Sodium is most abundant in blood plasma, and water follows sodium. For example, when the plasma has a high sodium content, high levels of fluid in the plasma will occur. The normal range for sodium is 135-145 mEq/L.

Hyponatremia, or sodium level less than 135, is basically the result of having more water than sodium. It is most commonly caused by diuretics, diarrhea, congestive heart failure, liver disease, or renal failure. Signs and symptoms are primarily neurologic, due to the shift of water into brain cells causing edema. These include headaches, confusion, seizures, and coma. Other symptoms include nausea/vomiting, muscle weakness, fatigue, restlessness, and irritability. Treatment includes correcting the underlying cause, diuretic medications, IV sodium, and fluid restrictions.

Hypernatremia, or sodium level higher than 145, results from too much sodium, not enough water. It can occur from various factors including dehydration, fever, diabetes insipidus, Cushing’s Syndrome, long exposure to environmental heat, or extensive exercise. Signs and symptoms of hypernatremia include thirst, dry mucous membranes and skin, edema, agitation, restlessness, confusion, diminished cardiac output, and in severe cases, seizures and coma. Like other electrolyte disorders, treatment of hypernatremia includes the correction and management of underlying causes by administering diuretics, measuring I/O, dialysis, and decreasing sodium intake.

Remember, know the normal ranges and the basic function of the primary electrolytes—this will really help you in answering questions related to fluid and electrolyte balance.


Let’s look at a couple of sample questions.

1. A nurse is caring for a patient with a calcium level of 7.5 mg/dL. Which nursing interventions are necessary based on this calcium level? Choose all that apply.

  1. Assess for positive Trousseau sign
  2. Implement seizure precautions
  3. Administer IV calcium gluconate
  4. Implement continuous cardiac monitoring


2. A patient with a potassium level of 2.5 mEq/L will exhibit the following symptoms:

  1. Muscle irritability, then weakness; tall peaked T waves
  2. Increased DTR’s, neuromuscular irritability, confusion
  3. Muscle weakness, numbness/tingling, flattened T waves, U waves
  4. Relaxed muscles, vasodilation, hypotension, decreased DTR’s


Great job! Thanks for watching this video tutorial on fluid and electrolyte balance! Hope this helps you in your studies!

Frequently Asked Questions


What are electrolytes?


Electrolytes are ions that carry either a positive or negative charge. Exact concentrations of electrolytes are vital to body pH and overall homeostasis. These electrically charged ions move fluids within the body, produce energy, contract muscles, and perform many other roles in the body.


How much of the body’s weight consists of water?


Water makes up approximately 55-60% of the body’s weight and is involved in many critical functions, including maintenance of blood volume, cellular transport of vital substances such as oxygen and glucose, transport of waste products to the lungs and kidneys for removal, lubrication and cushioning, the breakdown of food in the digestive system, providing a medium for chemical reactions in cells, and maintenance of body temperature.


What is fluid balance?


Fluid balance refers to the homeostasis of all bodily fluids both inside the cell (intracellular fluid) and outside the cell (extracellular fluid) and is impacted by the amount of water taken in and the amount of water removed from the body (via excretion, perspiration, nausea/vomiting, etc).


What is intracellular fluid?


Intracellular fluid is fluid that is located within the cells of the body. It makes up about 40% of the body’s weight and consists mostly of water, proteins, and electrolytes.


What is extracellular fluid?


Extracellular fluid is fluid located outside of and surrounding the cell. It is found in blood’s plasma, cerebrospinal fluid, interstitial fluid, lymph fluid, and the other fluids that protect the body’s organs and line the body’s cavities.


What are the main electrolytes in the body?


The major intracellular electrolytes are potassium and magnesium. The major extracellular electrolytes are sodium and chloride.


What is the role of and normal range for potassium?


Potassium is responsible for intracellular excitation critical to cardiac function. The normal range for serum potassium is 3.5-5 mEq/L.


What is the role of and normal range for magnesium?


Magnesium is responsible for maintaining appropriate muscular relaxation. The normal range for serum magnesium is 1.5-2.5 mEq/L.


What is the role of and normal range for sodium?


Sodium is responsible for the functioning of muscles and the central nervous system. The normal range for serum sodium is 135-145 mEq/L.


What is the role of and normal range for calcium?


Calcium is responsible for neuronal excitability (including cardiac neuronal excitability) and bone growth and development. The normal range for serum calcium is 8.5-10.5 mg/dL.


What is the role of and normal range for chloride?


Chloride is important in the maintenance of homeostasis of fluid and electrolytes. The normal range for serum chloride is 95-105 mEq/L.


What is the role of and normal range for phosphorus?


Phosphorus is critical to bone development and cellular growth. The normal range for serum phosphorus is 2.5-4.5 mg/dL.


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by Mometrix Test Preparation | Last Updated: June 20, 2024