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💧 NCLEX guideUpdated October 202610 min read4 practice questions

NCLEX fluid and electrolytes: imbalances, IV fluids and ABGs

Fluid and electrolyte items test patterns. Low calcium and low magnesium make nerves and muscles irritable: tingling, tetany, seizures. High calcium and high magnesium make them sluggish: weakness, lost reflexes, slow breathing. Potassium is dangerous at both ends because of the heart: peaked T waves when high, flat T waves and U waves when low. Sodium problems show up in the brain. ABGs take three steps: pH, ROME, compensation.

Normal ranges, and why your book may differ

Ranges vary by laboratory and textbook. Learn the common review ranges, and use the range printed in the item when there is one. The rest of the panel is in the NCLEX lab values guide.

ElectrolyteCommon review rangeOther published ranges
Sodium135–145 mEq/L136–145 mEq/L
Potassium3.5–5.0 mEq/Lupper limit 5.1 or 5.2 mEq/L
Calcium (total)9.0–10.5 mg/dL8.3–10.2 or 8.6–10.2 mg/dL
Magnesium1.5–2.5 mEq/L1.3–2.1 or 1.5–2.4 mEq/L
Phosphorus2.5–4.5 mg/dL3.0–4.5 or 2.5–4.0 mg/dL

High and low: the signs of each imbalance

ImbalanceCommon causesWhat the exam shows youNursing focus
Hypokalemia (K below 3.5)Loop and thiazide diuretics, vomiting, NG suction, diarrhea, insulinWeakness, cramps, constipation, flat T waves and U waves; digoxin toxicity more likelyCardiac monitor; replace by mouth or IV pump; urine output first
Hyperkalemia (K above 5.0)Kidney failure, potassium-sparing diuretics, ACE inhibitors, burns, crush injuries, acidosisWeakness, paresthesias, slow irregular pulse, peaked T wavesCardiac monitor; stop potassium; calcium gluconate, insulin with dextrose, removal
Hyponatremia (Na below 135)SIADH, fluid excess, diuretics, hypotonic fluidsHeadache, nausea, confusion, seizuresSeizure precautions; fluid restriction for SIADH; 3% saline if severe; correct slowly
Hypernatremia (Na above 145)Water loss, too little water, diabetes insipidusThirst, dry mucous membranes, restlessness, seizuresReplace water slowly to avoid cerebral edema
HypocalcemiaThyroid or parathyroid surgery, low vitamin D, kidney disease, pancreatitisTingling of mouth and fingers, tetany, Chvostek's and Trousseau's signs, laryngospasm, prolonged QTIV calcium gluconate; seizure precautions; watch the airway
HypercalcemiaHyperparathyroidism, cancer, immobilityWeakness, confusion, constipation, kidney stones, shortened QTIV fluids, then calcium-lowering drugs as ordered; mobilize
HypomagnesemiaAlcohol use disorder, malnutrition, diuretics, proton pump inhibitorsTremor, hyperactive reflexes, tetany, seizures, torsades; often low K and Ca tooReplace magnesium; seizure precautions; monitor
HypermagnesemiaKidney failure, magnesium sulfate infusions, magnesium antacids and laxativesDiminished or lost deep tendon reflexes, lethargy, low BP, bradycardia, slow breathingStop the magnesium; calcium gluconate
HypophosphatemiaRefeeding after starvation, alcohol use disorder, DKAMuscle and respiratory weakness, confusion, rhabdomyolysisRefeed slowly; replace phosphate
HyperphosphatemiaKidney failureMostly the signs of the low calcium it causesPhosphate binders with meals, low-phosphate diet

The shortcut: calcium and magnesium share a pattern (low twitches, high sedates), phosphorus moves opposite to calcium, potassium weakens muscles both ways while the ECG tells them apart, and sodium is the brain. Potassium: The Electrolyte That Stops Hearts and Sodium, Calcium and Magnesium: Twitching, Seizing and Going Flat drill them.

Potassium and the ECG

  • High potassium changes the ECG in order as it climbs: tall peaked T waves, then flattened or lost P waves, then a widened QRS, then a sine wave and asystole. How fast it rose matters as much as the number.
  • Low potassium flattens the T wave and brings out a U wave, often with ST depression, and raises the risk of arrhythmias, especially with digoxin.

A high potassium with no ECG changes and no cause may be a hemolyzed sample and is usually redrawn; with ECG changes, treat first.

Chvostek's and Trousseau's signs

Both show the nerve and muscle irritability of low calcium (low magnesium can cause them too):

  • Chvostek's sign: tap the facial nerve in front of the ear; the facial muscles or upper lip twitch.
  • Trousseau's sign: inflate a blood pressure cuff about 20 mmHg above systolic for 2 to 3 minutes; the hand and wrist go into carpal spasm. It is the more specific of the two.

The classic setting is the day after a thyroidectomy or parathyroidectomy: tingling around the mouth first, laryngospasm next. Check the signs, keep IV calcium gluconate available, report. A positive sign never means high calcium.

IV fluids: isotonic, hypotonic, hypertonic

TypeExamplesWhat it doesUse it forWatch for
Isotonic0.9% sodium chloride (normal saline), lactated Ringer'sStays in the vessels; no net shiftHypovolemia: blood loss, shock, burns, vomiting, diarrhea. Normal saline is the only fluid run with bloodOverload in heart or kidney failure: crackles, JVD, weight gain
Hypotonic0.45% sodium chlorideMoves water into cellsCellular dehydration, hypernatremiaNever with increased intracranial pressure; worsens hypotension
Hypertonic3% and 5% sodium chloridePulls water out of cellsSevere symptomatic hyponatremia; cerebral edema in critical carePulmonary edema; frequent sodium checks; slow, by pump

D5W is isotonic in the bag but acts as free water once the dextrose is used, so it is no volume expander and is avoided with increased intracranial pressure. D5 in 0.45% saline, D5 in 0.9% saline and D5 in lactated Ringer's are hypertonic in the bag. IV Fluids, Potassium Rules and the First 15 Minutes of a Transfusion covers IV safety.

IV potassium rules

  • Never IV push, never undiluted. The FDA label for potassium chloride concentrate says it "must be diluted before administration" and is "not for direct patient injection"; a bolus can stop the heart.
  • Always by infusion pump, ideally from a premixed bag.
  • Rate: the label's usual limit is 10 mEq per hour when serum potassium is above 2.5 mEq/L. Faster rates follow facility policy, usually by central line with continuous cardiac monitoring.
  • Urine output and kidney function first: potassium leaves through the kidneys.
  • Watch the site: IV potassium irritates veins; if the site hurts, check for infiltration or phlebitis.
  • Oral potassium goes with food and a full glass of water; extended-release tablets are not crushed.

"KCl 40 mEq IV push" is an order to question, not to adjust: diluting it and pushing it slowly is still wrong.

ABG interpretation in three steps (ROME)

Normal values: pH 7.35–7.45, PaCO₂ 35–45 mmHg, HCO₃⁻ 22–26 mEq/L (some labs run bicarbonate to 29).

  1. pH: below 7.35 is acidosis, above 7.45 is alkalosis.
  2. ROME, Respiratory Opposite, Metabolic Equal: PaCO₂ moving opposite to the pH means respiratory; HCO₃⁻ moving the same way as the pH means metabolic.
  3. Compensation: other value normal, uncompensated. Other value abnormal in the direction that pulls the pH back toward normal: partially compensated while the pH is still abnormal, fully once it is in range. In a fully compensated gas, the side of 7.40 the pH sits on names the original problem.

The lungs compensate within minutes, the kidneys over hours to days, which is why long-standing COPD often shows a high PaCO₂, a high HCO₃⁻ and a near-normal pH.

DisorderPatternCommon causes
Respiratory acidosispH low, PaCO₂ highHypoventilation: COPD, opioid or sedative overdose, airway obstruction
Respiratory alkalosispH high, PaCO₂ lowHyperventilation: anxiety, pain, fear, overventilation
Metabolic acidosispH low, HCO₃⁻ lowDKA, kidney failure, severe diarrhea, shock; Kussmaul breathing is the lungs compensating
Metabolic alkalosispH high, HCO₃⁻ highVomiting, NG suction, diuretics, excess antacids; often low potassium

ABGs in Three Steps: ROME runs the steps on practice gases.

The traps, and two worked examples

  • Low potassium with digoxin is a priority even at a normal digoxin level.
  • Chronic hyponatremia is corrected slowly, generally no more than about 8 to 10 mEq/L in 24 hours; a fast rise causes osmotic demyelination.
  • Vomiting and NG suction cause metabolic alkalosis; diarrhea causes metabolic acidosis.

1. A client with diabetic ketoacidosis has pH 7.29, PaCO₂ 30 mmHg, HCO₃⁻ 15 mEq/L. How should the nurse interpret these results? pH low: acidosis. HCO₃⁻ low, same direction: metabolic. PaCO₂ low, pushing the pH up, with the pH still below 7.35. Partially compensated metabolic acidosis. The deep, rapid breathing is that compensation.

2. A client with chronic kidney disease missed two dialysis sessions. Potassium is 6.8 mEq/L and the monitor shows peaked T waves. Which order should the nurse carry out first?

  1. Sodium polystyrene sulfonate by mouth. Removes potassium, but over hours. Not first.
  2. Calcium gluconate IV. Stabilizes the heart without lowering the potassium. First.
  3. Regular insulin IV with dextrose. Shifts potassium into cells; check glucose after. Next.
  4. Prepare for hemodialysis. The definitive fix, but it takes time. Later.

With ECG changes: protect the heart, shift, then remove. The fluid and electrolyte practice questions repeat these patterns.

✅ Test yourself: 4 questions

Four fluid and electrolyte items. Name the imbalance, or what the fluid is for, before you read the options. Every client is fictional; exam practice only, not medical advice.

Question 1 of 4

A client with acute pancreatitis is being treated on a medical unit. Which finding requires the nurse's immediate follow-up?

  1. Pain that eases when the client sits up and leans forward
  2. Tingling around the mouth with twitching of the facial muscles
  3. Epigastric pain that radiates through to the back
  4. A serum lipase three times the upper limit of normal
Show the answer and rationale

Answer: B

In pancreatitis, fatty acids released from damaged tissue bind calcium, so perioral tingling and facial twitching signal hypocalcemia that can progress to tetany, laryngospasm, and dysrhythmias. Epigastric pain radiating to the back and a lipase above three times normal are the diagnostic features of the disease itself. Sitting up and leaning forward often eases the pain and is an expected finding.

📚 Learn it: Sodium, Calcium and Magnesium: Twitching, Seizing and Going Flat

Question 2 of 4

An older adult with heart failure is receiving a second unit of packed red blood cells. Ninety minutes into the unit, the client is short of breath with crackles in both lungs, the blood pressure has risen from 138/80 to 176/98 mm Hg, and the neck veins are distended. After stopping the transfusion, which prescription should the nurse anticipate?

  1. IV furosemide to remove the excess volume
  2. A normal saline bolus to protect the kidneys
  3. IV diphenhydramine to block histamine
  4. Oral acetaminophen to reduce a fever
Show the answer and rationale

Answer: A

Dyspnea, crackles, a rising blood pressure, and distended neck veins during a transfusion describe transfusion-associated circulatory overload, which is most likely in older adults and clients with heart failure; after the transfusion is stopped and the client is seated upright with oxygen, a diuretic removes the excess volume. Diphenhydramine treats an allergic reaction with hives and itching, and acetaminophen treats a febrile reaction. A saline bolus supports kidney perfusion in an acute hemolytic reaction but would worsen overload here.

📚 Learn it: IV Fluids, Potassium Rules and the First 15 Minutes of a Transfusion

Question 3 of 4

A client with metastatic breast cancer is admitted with confusion, constipation, frequent urination, and a serum calcium of 14.2 mg/dL. Which prescription should the nurse implement first?

  1. 0.9% sodium chloride IV at the prescribed rate
  2. Zoledronic acid IV over 15 minutes
  3. A stool softener and assistance with walking
  4. Furosemide 40 mg by IV push
Show the answer and rationale

Answer: A

Hypercalcemia causes polyuria that leaves the client volume depleted, which further reduces calcium excretion, so isotonic saline comes first to restore volume and help the kidneys excrete calcium. A bisphosphonate such as zoledronic acid is also prescribed, but it takes 2 to 4 days to lower the calcium, and calcitonin can be added for a faster, short-lived effect. A loop diuretic is used only after volume is restored, if at all, because giving it to a dehydrated client worsens the problem, and treating the constipation can wait.

📚 Learn it: Sodium, Calcium and Magnesium: Twitching, Seizing and Going Flat

Question 4 of 4

A unit of packed red blood cells arrives for a client just as the client's only IV catheter infiltrates. The IV team will not be able to place a new catheter for about 90 minutes. What should the nurse do with the unit?

  1. Keep it at the bedside and run it faster once access is in
  2. Start it through the infiltrated catheter at a slow rate
  3. Return it to the blood bank until IV access is ready
  4. Store it in the unit's medication refrigerator for now
Show the answer and rationale

Answer: C

Blood is stored only in monitored blood bank refrigerators, and a red cell unit should be started within about 30 minutes and completed within 4 hours of leaving the blood bank, so a unit that cannot be started promptly goes back. A unit medication refrigerator is not monitored for blood storage, a 90-minute delay followed by a rushed infusion risks bacterial growth and circulatory overload, and an infiltrated catheter is never used.

📚 Learn it: IV Fluids, Potassium Rules and the First 15 Minutes of a Transfusion

Practice 10 physiological adaptation questions →

Electrolytes, ABGs and other Physiological Adaptation items with a rationale after each one, misses saved to Weak Spots. Free, no sign-up.

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❓ Frequently asked

What are the normal electrolyte ranges for the NCLEX?

Common review ranges: sodium 135 to 145 mEq/L, potassium 3.5 to 5.0 mEq/L, total calcium about 9.0 to 10.5 mg/dL, magnesium about 1.5 to 2.5 mEq/L, phosphorus about 2.5 to 4.5 mg/dL. Labs differ slightly; when an item prints a range, use it.

What ECG changes go with high and low potassium?

High: peaked T waves first, then flattened P waves, a widened QRS, and finally a sine wave and asystole. Low: flattened T waves, U waves and ST depression, with more arrhythmias, especially on digoxin.

Why is potassium never given IV push?

A bolus can cause fatal arrhythmias or cardiac arrest. The concentrate must be diluted and given by pump, usually no faster than 10 mEq per hour unless policy allows more with cardiac monitoring.

How do you interpret an ABG with ROME?

Check the pH for acidosis or alkalosis. Respiratory Opposite, Metabolic Equal: a PaCO2 moving opposite to the pH means respiratory, a bicarbonate moving with it means metabolic. Then see whether the other value is normal (uncompensated) or pulling the pH back toward normal (compensating).

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📚 Learn it in the app's lessons

Sources

  1. OpenStax, Clinical Nursing Skills, Appendix A: Adult Lab Values
  2. OpenStax, Medical-Surgical Nursing, 10.2 Fluid Disturbances and Replacement (isotonic, hypotonic and hypertonic IV fluids)
  3. OpenStax, Medical-Surgical Nursing, 10.3 Electrolyte Imbalance (ranges, Chvostek's and Trousseau's signs, potassium never IV push)
  4. OpenStax, Medical-Surgical Nursing, 10.4 Acid-Base Imbalance (ROME, compensation, causes)
  5. FDA label via DailyMed (NIH), Potassium Chloride for Injection Concentrate, B. Braun: must be diluted, not for direct injection, usual limit 10 mEq/hour
  6. StatPearls (NIH Bookshelf), Hyperkalemia (ECG progression; calcium first, insulin with dextrose, dialysis; updated Dec. 2025)
  7. StatPearls (NIH Bookshelf), Hyponatremia (correction limits, 3% saline, osmotic demyelination; updated June 2026)
  8. StatPearls (NIH Bookshelf), Trousseau Sign (how it is elicited; more specific than Chvostek's)
  9. StatPearls (NIH Bookshelf), Hypermagnesemia
  10. StatPearls (NIH Bookshelf), Hypophosphatemia (refeeding, alcohol use disorder, severe weakness)
  11. MedlinePlus Medical Encyclopedia (NIH), High potassium level (causes, emergency treatment; reviewed Oct. 2025)

Accessed October 2026. Yearly figures name their year; NCSBN publishes a new statistics brief each June and a new test plan every three years (next: April 2029). Exam preparation only, never medical advice. NCLEX® is a registered trademark of NCSBN, which does not endorse this site.

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