Fluid and Electrolyte Questions for the Prometric Nursing Exam 2026: 20 MCQs with Answers on IV Fluids, Dehydration, Fluid Overload, Sodium, Potassium, Calcium, Magnesium, Acid-Base and Blood Gas Interpretation

Fluid, electrolyte and acid-base questions appear across the medical-surgical, critical care and pharmacology domains of the registered nurse paper, usually 8 to 12 questions in total, and they are the ones most often answered from memory rather than understanding. The exam wants three things: the normal ranges, the signs of each imbalance, and the nursing action that is safe. This set covers what recurs; the drug maths is in the drug calculation set.

Intravenous fluids

Question 1

Which intravenous fluid is isotonic and appropriate for initial volume replacement in a hypovolaemic adult?

1. 0.45% sodium chloride
2. 0.9% sodium chloride, Hartmann's solution (Ringer's lactate) or a balanced crystalloid such as Plasma-Lyte
3. 5% dextrose in water
4. 3% sodium chloride

Answer: B. 5% dextrose is isotonic in the bag but becomes hypotonic once the glucose is metabolised, so it does not expand the intravascular space; 0.45% saline is hypotonic; 3% saline is hypertonic and used only for severe symptomatic hyponatraemia under close monitoring.

Question 2

A patient with cerebral oedema after a head injury is prescribed intravenous fluids. Which fluid should the nurse question?

1. 0.9% sodium chloride
2. 5% dextrose or 0.45% sodium chloride, because hypotonic fluids shift water into cells and worsen cerebral oedema
3. Hypertonic saline per protocol
4. Mannitol per protocol

Answer: B. Hypertonic fluids and mannitol draw fluid out of swollen brain cells; the nurse checks every bag against the patient's condition, not just the prescription.

Question 3

Which patient is at greatest risk of fluid volume overload from intravenous therapy?

1. A 25-year-old with gastroenteritis
2. An 80-year-old with heart failure and chronic kidney disease receiving maintenance fluids
3. A 40-year-old post-appendicectomy
4. A 30-year-old marathon runner

Answer: B. Older age, cardiac and renal disease reduce the capacity to handle fluid; signs of overload are weight gain, oedema, raised jugular venous pressure, crackles, breathlessness and a bounding pulse.

Question 4

The nurse assesses a patient with fluid volume deficit. Which findings are expected?

1. Bounding pulse, hypertension, crackles
2. Tachycardia, postural hypotension, dry mucous membranes, reduced skin turgor, concentrated urine with a high specific gravity, raised urea and haematocrit, and reduced urine output below 0.5 mL/kg/h
3. Weight gain of 2 kg overnight
4. Distended neck veins

Answer: B. Daily weight is the most reliable measure of fluid balance; 1 kg of weight change is about 1 litre of fluid.

Sodium

Question 5

A patient with heart failure on a thiazide has a sodium of 124 mmol/L, headache, nausea and confusion. Which nursing actions are appropriate?

1. Encourage three litres of oral fluid daily
2. Implement seizure precautions and neurological observations, restrict fluids as prescribed, hold the thiazide pending medical review, monitor sodium levels, and expect a slow correction of no more than 8 to 10 mmol/L in 24 hours
3. Give a rapid infusion of 0.9% saline
4. Give a salt-free diet

Answer: B. Rapid correction of chronic hyponatraemia causes osmotic demyelination; hypertonic saline is reserved for seizures or severe symptoms and given under close monitoring.

Question 6

An elderly patient with dementia in a hot climate has a sodium of 158 mmol/L, dry sticky mucous membranes, agitation and a low-grade fever. The most likely cause and the management are:

1. Excess intravenous saline; diuretics
2. Water deficit from inadequate intake and insensible losses; oral water or hypotonic intravenous fluids as prescribed, lowering sodium slowly (no faster than about 10 mmol/L in 24 hours) to avoid cerebral oedema, with careful monitoring
3. SIADH; fluid restriction
4. Normal finding in the elderly

Answer: B. Hypernatraemia is common in patients who cannot access water, especially in Gulf summers; thirst is the first defence and is blunted in the elderly.

Potassium

Question 7

A patient on furosemide has a potassium of 2.9 mmol/L. Which assessment findings and ECG changes are expected?

1. Peaked T waves and diarrhoea
2. Muscle weakness, cramps, constipation, paralytic ileus, fatigue, and ECG changes of flattened T waves, ST depression and prominent U waves, with increased risk of digoxin toxicity
3. Hyperreflexia
4. Widened QRS and bradycardia

Answer: B. Hypokalaemia potentiates digoxin; the nurse checks digoxin levels and heart rate when both are present.

Question 8

Intravenous potassium chloride 40 mmol in 1,000 mL is prescribed. Which administration practice is correct?

1. Give undiluted potassium chloride as an IV push
2. Use a pre-mixed bag where available, never add concentrated potassium to a hanging bag, infuse via a pump at no more than 10 mmol/h through a peripheral line (up to 20 mmol/h with cardiac monitoring per policy), check urine output before starting, and monitor the site for phlebitis
3. Infuse 40 mmol over 30 minutes
4. Add it to a bag of blood

Answer: B. Concentrated potassium is a high-alert medication stored separately; IV push potassium is fatal and the classic examination wrong answer.

Question 9

A patient with acute kidney injury has a potassium of 6.8 mmol/L with peaked T waves. The nurse's first actions are:

1. Give oral potassium binder and recheck in the morning
2. Place the patient on a cardiac monitor, stop any potassium-containing fluids or supplements, notify the doctor urgently, and prepare intravenous calcium gluconate, insulin with dextrose and nebulised salbutamol per protocol, with dialysis if refractory
3. Encourage bananas and orange juice
4. Give a potassium-sparing diuretic

Answer: B. Calcium protects the heart within minutes; insulin and salbutamol shift potassium into cells within 30 minutes; binders and dialysis remove it.

Question 10

Which food list should the nurse teach a dialysis patient with hyperkalaemia to limit?

1. White rice, apples, cucumber
2. Bananas, oranges and orange juice, potatoes, tomatoes, dried fruit, dates, spinach, avocados, and salt substitutes containing potassium chloride
3. Bread and pasta
4. Chicken breast and eggs

Answer: B. Dates are a staple in Gulf diets and are high in potassium; leaching vegetables by boiling reduces potassium content.

Calcium, magnesium and phosphate

Question 11

Twelve hours after a total thyroidectomy, a patient reports tingling around the mouth and in the fingertips, and the nurse notes carpal spasm when the blood pressure cuff is inflated. The findings indicate:

1. Hypercalcaemia; give fluids
2. Hypocalcaemia from parathyroid injury (positive Trousseau sign, with Chvostek sign on tapping the facial nerve); check calcium, notify the surgeon, prepare intravenous calcium gluconate, keep the airway equipment at hand for laryngospasm, and monitor for seizures and prolonged QT
3. Anxiety; reassure
4. Hypokalaemia; give potassium

Answer: B. Post-thyroidectomy nurses monitor for haemorrhage, airway compromise, hypocalcaemia and recurrent laryngeal nerve injury (hoarseness).

Question 12

A patient with bone metastases has a corrected calcium of 3.3 mmol/L, confusion, constipation, polyuria and thirst. Nursing management includes:

1. Fluid restriction and calcium supplements
2. Intravenous isotonic saline hydration as prescribed, strict intake and output, safety measures for confusion, mobilisation where possible, administering a bisphosphonate or calcitonin as prescribed, and monitoring the ECG for a shortened QT interval
3. Thiazide diuretics
4. Vitamin D supplements

Answer: B. Loop diuretics may be added after rehydration; thiazides raise calcium and are stopped.

Question 13

A patient with alcohol use disorder and poor nutrition has a magnesium of 0.45 mmol/L. Which findings and risks should the nurse anticipate?

1. Hyporeflexia and bradycardia
2. Tremor, hyperreflexia, tetany, confusion, and cardiac arrhythmias including torsades de pointes, with coexisting hypokalaemia and hypocalcaemia that will not correct until magnesium is replaced
3. Constipation
4. Flushing and hypotension

Answer: B. Hypermagnesaemia (for example from magnesium sulfate in pre-eclampsia or antacids in renal failure) causes the opposite: lost reflexes, respiratory depression and bradycardia, reversed with calcium gluconate.

Question 14

A severely malnourished patient started on enteral feeding develops a phosphate of 0.4 mmol/L, weakness and confusion on day 3. The nurse recognises:

1. Normal adaptation to feeding
2. Refeeding syndrome, with hypophosphataemia, hypokalaemia and hypomagnesaemia, requiring slowing of feeds, electrolyte replacement and thiamine as prescribed, and cardiac monitoring; prevention is to start feeding at a low rate with prophylactic thiamine and electrolyte checks in at-risk patients
3. Sepsis
4. Hyperglycaemia only

Answer: B. Risk factors include BMI under 16, minimal intake for over 5 to 10 days, alcohol misuse and anorexia nervosa.

Acid-base and blood gases

Question 15

Arterial blood gas: pH 7.28, PaCO₂ 7.5 kPa (56 mmHg), HCO₃⁻ 26 mmol/L, PaO₂ 8.0 kPa. The interpretation is:

1. Metabolic acidosis
2. Acute respiratory acidosis, uncompensated, as seen in opioid overdose, acute asthma exhaustion or COPD exacerbation; the nursing priority is to improve ventilation and call for help
3. Respiratory alkalosis
4. Metabolic alkalosis

Answer: B. Low pH with a raised carbon dioxide is respiratory acidosis; a raised bicarbonate would indicate chronic compensation.

Question 16

Arterial blood gas: pH 7.52, PaCO₂ 3.5 kPa (26 mmHg), HCO₃⁻ 23 mmol/L. The patient is anxious and hyperventilating with tingling fingers. The interpretation and action are:

1. Metabolic acidosis; give bicarbonate
2. Respiratory alkalosis from hyperventilation; stay with the patient, coach slow breathing, and look for underlying causes such as pain, hypoxia, sepsis, pulmonary embolism or salicylate poisoning before attributing it to anxiety
3. Respiratory acidosis; increase oxygen
4. Normal

Answer: B. Alkalosis lowers ionised calcium, producing paraesthesia and carpopedal spasm.

Question 17

Arterial blood gas: pH 7.20, PaCO₂ 3.0 kPa (22 mmHg), HCO₃⁻ 9 mmol/L, glucose 28 mmol/L, ketones positive. The interpretation is:

1. Respiratory acidosis
2. Metabolic acidosis with partial respiratory compensation (Kussmaul breathing), consistent with diabetic ketoacidosis; priorities are fluids, insulin infusion, potassium replacement and hourly monitoring per protocol
3. Metabolic alkalosis
4. Mixed alkalosis

Answer: B. Other causes of metabolic acidosis are lactic acidosis in shock, renal failure, severe diarrhoea and poisoning; potassium falls rapidly once insulin starts.

Question 18

A patient with prolonged vomiting and nasogastric suction has pH 7.50, PaCO₂ 6.0 kPa, HCO₃⁻ 36 mmol/L and a potassium of 3.0 mmol/L. The interpretation is:

1. Respiratory acidosis
2. Metabolic alkalosis with respiratory compensation from loss of gastric acid, with associated hypokalaemia; treatment is isotonic saline and potassium replacement, treating the cause, and antiemetics
3. Metabolic acidosis
4. Normal blood gas

Answer: B. Loop diuretics and excess antacids also cause metabolic alkalosis; the kidneys cannot excrete bicarbonate while chloride and potassium are depleted.

Monitoring

Question 19

A post-operative patient's urine output has been 20 mL/h for the past two hours. Weight 70 kg. The nurse should:

1. Document and reassess in four hours
2. Recognise oliguria (below 0.5 mL/kg/h, that is below 35 mL/h for this patient), check the catheter for kinks or blockage, assess for hypovolaemia and bleeding, check vital signs and recent fluid balance, and notify the surgical team for review and possible fluid challenge
3. Give furosemide
4. Clamp the catheter

Answer: B. Oliguria is an early sign of hypovolaemia and acute kidney injury; a diuretic without assessing volume status worsens pre-renal injury.

Question 20

Which patient's fluid balance chart requires the nurse to intervene first?

1. A patient drinking 1.5 litres with output of 1.4 litres
2. A heart failure patient with a positive balance of 2.5 litres over 24 hours, a weight gain of 2 kg and new bibasal crackles
3. A patient with a negative balance of 300 mL after diuretics as intended
4. A patient with equal intake and output

Answer: B. Accurate charting includes IV fluids, flushes, enteral feeds, oral intake, urine, drains, vomit and stool; insensible losses of 500 to 800 mL a day rise with fever and in hot climates.

How to practise

• Learn the normal ranges: sodium 135 to 145, potassium 3.5 to 5.0, calcium 2.2 to 2.6 (corrected), magnesium 0.7 to 1.0, phosphate 0.8 to 1.5 mmol/L; pH 7.35 to 7.45, PaCO₂ 4.7 to 6.0 kPa, bicarbonate 22 to 26.
• Use a two-step blood gas method: pH tells you acidosis or alkalosis; whichever of carbon dioxide or bicarbonate moved in the direction that explains the pH is the primary problem.
• Know the high-alert rules: potassium rate limits, slow sodium correction, calcium for hyperkalaemia and magnesium toxicity.

Medical-surgical and critical care chapters with explanations are in the Registered Nurse bank; related sets are the medical-surgical questions, critical care questions and pharmacology questions. The domain weighting is in the DHA nursing syllabus.

Frequently asked questions

How many fluid and electrolyte questions are in the Prometric nursing exam?

About 8 to 12 of 150, spread across the medical-surgical, critical care and pharmacology domains.

Which electrolyte topics come up most?

Potassium (hypo- and hyperkalaemia, safe IV administration), sodium correction, post-thyroidectomy hypocalcaemia and blood gas interpretation.

Are blood gas questions in the nursing exam?

Yes. Expect two or three gases to interpret as respiratory or metabolic acidosis or alkalosis with the likely cause.

Which units does the exam use?

Mostly SI units (mmol/L, kPa), sometimes with conventional units in brackets; learn both for carbon dioxide and glucose.

Are these real exam questions?

No. They are original practice questions written to the published blueprint. Real exam content is confidential.