Fluids and Electrolytes Exam: A Study Guide By a 4.0 GPA Nursing Student (2025)

Are you lost on where and how to start studying for your fluids and electrolytes exam?

While I can’t put every piece of information in this blog post, and every school is different, you can treat this as a checklist. While this is a helpful guide, always follow your professor’s blueprints and study the information they stressed to you.

I got a 96% on my fluids and electrolytes exam and so here I will share with you what I believe you need to know to do well on your exam. Now I can’t make any guarantees, you have to do the work of course. But this is a great guide to getting your foundation started in my opinion.

So get your notepad ready, and your Quizlet ready to make. Let’s get into it.

*Disclosure: You agree that our articles are not a replacement for proper studying. Nursing procedures are rapidly changing, and state laws can vary. We encourage students to always check our content for accuracy, and always use the methods taught by your instructor, nurse manager, or local laws. You further agree never to hold Midlifenursing.com (and its associated apps, YouTube account, or social media channels) responsible for damages, failure of tests, or losses occurred.

1. Understand the difference between Extracellular and Intracellular fluids.

Understanding the difference between these is really going to help you with visualizing what is happening when administering IV fluids.

Extracellular key points:

• This is the fluid OUTSIDE the cell
• The two main components are: plasma and interstitial fluid
• Examples of extracellular fluid are: Lymph, CSF, synovial fluid, pleural fluid, and peritoneal fluid.
• Has a high concentration of Na+ and a low concentration of K+
• When you hear third spacing, think extracellular fluid.
• When you think of edema, think extracellular fluid.

Intracellular key points:

• The fluid INSIDE the cell
• Most body fluid is intracellular
• Has a high concentration of K+ and a low concentration of Na+

2. Understand the very basics of diffusion and osmosis.

To do well on your fluids and electrolytes exam, you need to understand how the movement of water and solutes occurs in the body.

• Diffusion is when solutes move from an area of higher concentration to an area of lower concentration.
• Osmosis is when fluid moves from an area of lower concentration to an area of higher concentration.

One of the best ways to “see” this in action is when we are talking about dialysis where there is a semipermeable membrane involved. Dialysis uses an isotonic solution, and each patient has a personalized prescription that is input into the machine.

Using the processes of osmosis and diffusion, the machine and dialyzer filter the patient’s blood without losing red blood cells. How? Because they are too large to pass through the semi-permeable membrane. You should not need to know this for your fluids and electrolytes exam, but it is very helpful in getting a visual of how fluids and electrolytes work and move in the body.

I have a slight advantage with knowing dialysis super well because I am a former dialysis technician but I’ll insert a great and super short dialysis video here so you can get a visual.

3. KNOW the different fluid types.

• Isotonic solutions are the types of solutions you are going to use most of the time. This solution is the closest in composition to human cells. Isotonic solutions are used mainly for blood transfusions, fluid maintenance, and dehydration.
• Hypotonic solutions have a lower concentration of Na+, they are more dilute with water. When you think “hypo” I want you to think “hippo”. This solution will make the cell bigger, or make it swell. So it is fairly easy to remember because we use this to rehydrate the cells.
• Hypertonic solutions have a higher concentration of Na+ than the other fluid types. They are very salty. I want you to remember that these are rarely and very cautiously used. Usually, this solution is used only in the ICU in fluid overload emergencies and cerebral edema. I like to visualize it as the solution that will “pull the water” out of the swelling cells.

Know the fluid types and what categories they are in. For example, you should automatically know that lactated ringers are an isotonic solution, but so is 0.9% normal saline. These two fluids are what you will be administering most of the time as a nurse.

*Tip: Turn these tables into flashcards. On one side of the flashcard write “isotonic” and on the other side list the fluid types.

Fluid Types

If you are struggling to understand the different fluid types, I highly recommend this Nurse Sarah video right here. It is so important that you understand this information for your fluids and electrolytes exam.

4. Know the signs and symptoms of hypervolemia and hypovolemia

Knowing these signs and symptoms is SO important on exams. This is important because you of course need to know if your patient is showing signs of dehydration, but also overhydration. We have to be very careful to especially watch for signs of overhydration when we are administering fluids to patients with heart issues.

These are the most common “hallmark” signs to watch for:

5. Hypokalemia and Hyperkalemia.

We are starting with potassium because it is the most dangerous electrolyte imbalance. Potassium (K+) is a critical lab to watch for. Therefore, it is HUGE on exams.

The main causes of K+ imbalance you should know for tests are: kidney disease causing hyperkalemia and potassium wasting diuretics, nausea, and vomiting causing hypokalemia.

The normal range for K+ is 3.5 to 5.0 mEq/L

Signs and symptoms of Hyperkalemia vs Hypokalemia

As you can see, there are not really too many differences between hyperkalemia and hypokalemia. Therefore it is very important you know the lab range to decipher.

Also know the key symptoms of K+ being out of wack such as dysrhythmias, muscle cramping, and sudden weakness. In exam questions, you may have to pick the likely electrolyte imbalance out of calcium, sodium, and phosphorous. The mentioned above are tell-tale signs of K+ imbalance.

Big safety consideration: When a patient has a K+ imbalance and especially when getting K+ through IV piggyback, they must be placed on a telemetry monitor.

Important nursing interventions for K+ imbalance you should know

For hypokalemia:

• Administer potassium as ordered (could be orally or intravenously) **Check IV site frequently. Super dangerous if infiltrates. Can cause phlebitis.
• If the lab result is low due to potassium wasting diuretics, discontinue their use and contact the health care provider
• If the patient is weak, follow safety protocols to prevent falls
• Encourage eating foods high in potassium (see table at the end of this article)
• RED ALERT: NEVER IV PUSH POTASSIUM (it is administered through IV drip with a prescribed rate)

For hyperkalemia:

• If the patient is on a K+ IV drip and it is causing a high K+ result, discontinue use
• Administer IV insulin with hypertonic glucose if prescribed to rush the K+ back into the cells
• The patient will be on potassium restricted diet (teach NOT to use salt substitutes as they are high in K+)
• Administer potassium wasting diuretics as prescribed
• In critical cases, the patient may be taken to dialysis
• Administer IV calcium if prescribed

6. Hyponatremia and Hypernatremia

Sodium levels are our second most critical lab to watch for when it comes to electrolytes. This is also a super important electrolyte to know very well on a fluids and electrolytes exam.

When I think of sodium in the body, my first thought is the brain, and then I think about muscles.

The main causes of Na+ imbalance you should know for tests are: increased sodium intake and/or dehydration causing hypernatremia, and vomiting, and diarrhea causing hyponatremia.

The normal range for Na+ is 135-145 mEq/L

Signs and symptoms of Hypernatremia vs Hyponatremia

The biggest difference between hypernatremia and hyponatremia to know, in my opinion, are with hyponatremia you have a high risk for seizures. With hypernatremia, we have dry and sticky mucous membranes and signs and symptoms of fluid overload (ex: high BP and edema).

Important nursing interventions for Na+ imbalance you should know

For hyponatremia:

• Patient teaching to increase sodium intake as prescribed (Foods like bacon, and hotdogs)
• Treat the dehydration with IV saline as prescribed
• If the cause is fluid overload, resulting in Na+ dilution, administer diuretics as prescribed

For hypernatremia:

• Administer sodium wasting diuretics as prescribed
• A sodium restriction may be placed by the HCP
• Administer IV fluids as prescribed if the cause is fluid loss d/t nausea and vomiting for example

7. Hypocalemia and Hypercalemia

Calcium levels in our blood are extremely important for many functions, but I like to think of the heart and muscles first. This can get confusing because we think of those two systems with potassium too. However, there are some key standouts when it comes to calcium in exam questions and we will cover those here.

The main causes of Ca+ imbalance you should know for tests are: immobility and hyperparathyroidism for hypercalcemia, not eating enough calcium, and inadequate vitamin D intake for hypocalcemia.

The normal range for Ca+ is 9 to 10.5 mg/dL (some sources also say 8.5 to 10.5 mg/dL)

*Don’t get hung up on tiny differences with labs. Most tests will make it more obvious with being out of range in my experience.

Signs and symptoms of Hypercalcemia vs Hypocalcemia

In my experience, hypocalcemia is the most heavily tested on out of these two. Why? Because of the two very unique signs. Chvosteks and Trousseaus signs. I will leave a super short video with two awesome examples of these and what they look like right here.

Important nursing interventions for Ca+ imbalance you should know

For hypocalcemia:

• Administer oral and/or IV calcium as prescribed. Make sure you monitor for infiltration.
• Keep calcium gluconate at the bedside
• Give Vitamin D to increase calcium absorption
• Initiate seizure precautions
• Patient will be a fracture risk, so implement fall precautions
• Give dietary teaching for foods high in calcium

For hypercalcemia:

• Give dietary teaching to avoid foods high in calcium
• Discontinue any infusions containing calcium
• Administer calcium wasting diuretics as prescribed
• Teach weight bearing exercises (this puts Ca+ back into the bones)

8. Hypomagnesemia and Hypermagnesemia

When you think of magnesium for your fluids and electrolytes exam, think of the “chill out” electrolyte. My first thought when it comes to magnesium is reflexes and muscles.

Personally, in my fundamentals class, we didn’t talk too much about magnesium and it wasn’t heavily tested on, but you will for sure want to remember it for OB Maternity content.

The main causes of Mg+ imbalance you should know for tests are: taking too many antacids with magnesium for hypermagnesemia, and malnutrition, vomiting and diarrhea for hypomagnesemia.

The normal range for Mg+ is 1.3-2.1 mEq/L

Signs and symptoms of Hypermagnesemia vs Hypomagnesemia

I find the best way to memorize hyper and hypo magnesemia is to go back to the “chill out” trick. Too much magnesium, the muscles and reflexes are just too chilled out. They are low and slow. Too little magnesium, and everything is too excited, and “wired out”.

Important nursing interventions for Mg+ imbalance you should know

For hypomagnesemia:

• Administer magnesium sulfate IV as prescribed
• Initiate seizure precautions
• Give dietary teaching to encourage foods high in Mg+
• Assess DTRs frequently

For hypermagnesemia:

• Administer diuretics as prescribed to excrete excess magnesium
• Teach patient to avoid Mg+ containing antacids
• Teach patient to avoid high Mg+ foods
• Administer calcium gluconate as prescribed (this is the antidote for magnesium overdose)

9. Hypophosphatemia and Hyperphosphatemia

One helpful trick to know is that phosphorous and calcium act oppositely of each other. Meaning, that if calcium is high, phosphorous is going to be low.

So if you get a question where the patient is clearly showing signs and symptoms of hypocalcemia but the answer options don’t have that, but hyperphosphatemia IS there, you have a good chance of picking that option.

The main causes of PO4-3 imbalance you should know for tests are: kidney disease for hyperphosphatemia, and using magnesium-based antacids for hypophosphatemia.

The normal range for PO4-3 is 2.5-4.5 mEq/L

Signs and symptoms of Hyperphosphatemia vs Hypophosphatemia

If you compare this table to the calcium symptoms table, you will see the similarities. But remember, it is the opposite. So if phosphorous is high, symptoms will be similar to hypocalcemia. So if you really know your hyper and hypo calcemia, you should do well with figuring out which phosphorous imbalance you’re dealing with.

In my experience, phosphorous questions are usually used in a renal patient scenario where they need to be taught to take their phosphate binders.

Important nursing interventions for PO4-3 imbalance you should know

For hypophosphatemia:

• Administer phosphorous supplements as prescribed
• Fracture risk so implement fall precautions
• Patient teaching includes high phosphorous-containing foods

For hyperphosphatemia:

• Administer phosphorous binders as prescribed (excreted through stool)
• Patient teaching to avoid laxatives and enemas that contain phosphate
• Patient teaching to avoid high phosphorous-containing foods

Your fluids and electrolytes exam content will follow you all through nursing school

This may seem like a lot of information, and I agree, it is. However, once you grasp this specific content, it will make nursing school SO much easier for you going forward.

When you take exams and quizzes, everything must be applied to a real-life scenario. If you are paying attention in clinical, nurses are on top of a patient’s labs all through their shifts. Monitoring and assessing these labs is one of our main roles as an RN.

Think about it, if your patient all of a sudden is acting confused but their oxygen levels are normal, you definitely want to look at what their Na+ is doing because if they are hyponatremic, we need to implement seizure precautions and notify the provider right away.

If you take this specific content really seriously it is going to help you so much, including with ATI and HESIs.

10. Important food sources to know on your fluids and electrolytes exam

HESI and nursing exams love to test you on your knowledge of what foods go with which electrolytes. When you think about it, it is pretty important actually. If our patient is staying in the hospital, they are going to be eating. If we have a patient with hypernatremia, we probably don’t want them ordering a hotdog and chips.

Here is a table of, in my experience, the most important foods to know for your fluid and electrolytes exam.

In Conclusion:

Hopefully, this is a great head start in your studies for your fluid and electrolytes exam. I strongly feel that if you make sure to know these basics and foundations, you can easily build on them to master anything else your teacher has taught.

One more super important thing I suggest doing is taking practice tests!

After completing my junior year in nursing school I have definitely found my favorites. I will list a few right here:

• Fluid and Electrolytes COMPREHENSIVE Nursing NCLEX Quiz
• Hypotonic, Hypertonic, & Isotonic IV Solution Quiz for Nursing Students & NCLEX Exam
• Fluid & Electrolyte NCLEX Practice Quiz (120 Questions)

In conclusion, the best way to study for any exam is to practice, practice, practice. If you are new to nursing school, you may be pretty shocked at how different the tests are.

You can memorize this information all you want, but nursing school tests only care if you can apply it in real world scenarios.

If you need some more tips on how to study and do well on exams, you can read this article we wrote right here. These are some of my best tips for success to start getting really high grades in nursing school.

So good luck to you on your fluids and electrolytes exam! If you got all the way here, this shows you are dedicated and willing to do what it takes to succeed! Please let me know how your exam goes in the comments below.