NCLEX-RN Study Guide

NCLEX Fluid and Electrolytes Questions (2026)

November 2, 2026 · 5 min read · Reviewed for clinical accuracy by Dolma Tsering, RN

Short answer. Fluid and electrolyte NCLEX questions are about safety with numbers. Potassium is never given by intravenous push, sodium is corrected slowly, and the tonicity of the fluid decides which direction water moves.

What the 2026 NCLEX tests in this area

Physiological Adaptation: fluid volume deficit and excess, electrolyte imbalance
Pharmacological and Parenteral Therapies: IV fluid selection, replacement, monitoring

Key facts to know

Isotonic fluids	0.9 percent sodium chloride and lactated Ringer. Stay in the vascular space
Hypotonic fluids	0.45 percent sodium chloride. Move water into cells and can worsen cerebral edema
Hypertonic fluids	3 percent sodium chloride. Pull water out of cells and require close monitoring
Potassium administration rule	Never IV push. Dilute, infuse with a pump, and verify urine output first
Normal serum sodium	135 to 145 mEq/L
Correction speed for hyponatremia	Slowly, because rapid correction causes osmotic demyelination

Practice question from this chapter

A client with 2 days of diarrhea has a blood pressure that drops from 118/76 to 96/58 mmHg on standing, heart rate 112 beats/min, poor skin turgor, potassium 3.1 mEq/L, and sodium 130 mEq/L. Which action should the nurse implement first?

Encourage sports drinks and oral rehydration
Give an antidiarrheal medication
Restrict fluids until the diarrhea stops
Initiate intravenous fluids with potassium replacement as ordered

Show answer and rationale

Correct answer: D. Initiate intravenous fluids with potassium replacement as ordered

Orthostatic hypotension, tachycardia, and electrolyte depletion indicate significant dehydration, so intravenous fluids with potassium replacement are the correct first action. Oral rehydration is inadequate for this degree of depletion; antidiarrheals do not replace the losses; restricting fluids worsens dehydration.

Second practice question

A client with rhabdomyolysis from a crush injury has dark brown urine, a potassium level of 6.0 mEq/L, a creatinine of 3.1 mg/dL, and is receiving intravenous fluids. Which finding requires the most immediate action?

Potassium level of 6.0 mEq/L
Urine output of 90 mL over the last 2 hours
Serum creatinine of 3.1 mg/dL
Dark brown urine

Show answer and rationale

Correct answer: A. Potassium level of 6.0 mEq/L

The potassium level is correct because 6.0 mEq/L with ongoing muscle breakdown places the client at risk for lethal cardiac dysrhythmia and needs immediate treatment. Urine output of 45 mL/hour is adequate, the creatinine reflects the kidney injury already present, and dark urine is the expected finding that prompted treatment.

Tonicity decides the direction

Isotonic fluid replaces volume and stays in the vessels, which is why it is used for hypovolemia and shock. Hypotonic fluid hydrates cells and is used for cellular dehydration, but it can increase intracranial pressure. Hypertonic fluid pulls water out of cells and is used for severe hyponatremia or cerebral edema with strict monitoring.

When an item shows a client receiving 0.45 percent sodium chloride who is becoming confused, think sodium falling and cerebral edema, not a need for more hypotonic fluid.

Potassium is the safety item

Potassium moves cardiac conduction, so both the level and the rate of replacement matter. Never give a bolus. Verify renal function and urine output before giving a dose, use a pump, and teach the client to report burning at the site. A client on digoxin or a potassium sparing diuretic needs the level checked before the dose.

Signs that show the direction of the imbalance

Before you reach for a fluid, decide whether the client is dry, wet or cellular. Dry means tachycardia, low pressure, poor turgor and low urine output, and needs an isotonic bolus. Wet means crackles, oedema, raised jugular venous pressure and weight gain, and needs restriction and diuresis. Cellular dehydration with a high sodium means free water deficit, and hypotonic fluid is the answer.

Electrolytes follow their own signatures. Sodium disorders change the brain, so expect confusion and seizures. Potassium disorders change the heart, so expect weakness and dysrhythmias. Magnesium disorders amplify potassium problems, which is why they are replaced together.

Replacement safety

Potassium is the one that kills. Never give a bolus, verify urine output before each dose, use a pump, and teach the client to report burning at the site. Calcium and magnesium follow the same logic of slow, monitored replacement with cardiac monitoring.

Monitor the response, not just the dose. Repeat labs, urine output, weight and lung sounds tell you whether the replacement is working or is being overdone, and overdoing it produces the opposite problem within hours.

Frequently asked questions

Can potassium chloride be pushed IV?

Never. It must be diluted and infused with rate control. Rapid administration causes fatal dysrhythmias.

Which fluid is used for hypovolemic shock?

An isotonic crystalloid such as 0.9 percent sodium chloride or lactated Ringer, given as a bolus per protocol.

Why correct hyponatremia slowly?

Rapid correction can cause osmotic demyelination with permanent neurological damage.

What do I monitor during IV therapy?

Intake and output, daily weight, lung sounds, edema, and the electrolyte panel, plus the site for infiltration.

Why is 0.45 percent sodium chloride avoided after head injury?

It lowers serum osmolality and can shift water into brain cells, worsening cerebral oedema. Isotonic fluid is preferred in neuro injury.

What is the safest way to replace magnesium?

Slowly, with cardiac monitoring and a rate as prescribed, watching for flushing, hypotension and loss of deep tendon reflexes as signs of excess.

Free tool: the IV drip rate and dosage calculator shows the formula, the working and twelve practice problems with full rationales. No account needed.

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