NCLEX Fluid, Electrolyte & Acid-Base questions
The PrepScore bank has 61 Fluid, Electrolyte & Acid-Base questions, each with a rationale and two tags: the Client Needs category from the test plan and the clinical judgment step it tests. In this topic the items lean on Analyze cues and Recognize cues, which is worth knowing before you practise it. Three worked samples are below, answers behind a reveal.
Hypo/hyperNa with osmotic demyelination, hypo/hyperK with cardiac changes, hypo/hyperCa with tetany/coma, hypo/hyperMg, hypo/hyperPhos, fluid volume deficit/excess, ABG interpretation (4 disorders), mixed acid-base, F+E multi-patient priority.
Three worked questions
Q1. A 35-year-old male with chronic kidney disease arrives at the ED. The ED nurse reviews the ABG to identify the disturbance. Which ABG indicates COMPENSATED METABOLIC ACIDOSIS?
- A. pH 7.38, PaCO2 30, HCO3 18 (acidemia at low end of normal + low HCO3 primary + low PaCO2 respiratory compensation — compensated metabolic acidosis)
- B. pH 7.20, PaCO2 50, HCO3 20 (uncompensated mixed)
- C. pH 7.50, PaCO2 45, HCO3 30 (metabolic alkalosis)
- D. pH 7.40, PaCO2 40, HCO3 24 (normal)
Show answer and rationale
Answer: pH 7.38, PaCO2 30, HCO3 18 (acidemia at low end of normal + low HCO3 primary + low PaCO2 respiratory compensation — compensated metabolic acidosis)
Compensated metabolic acidosis: pH near-normal low end + HCO3 low (primary) + PaCO2 low (respiratory compensation). pH 7.38 + HCO3 18 + PaCO2 30 fits.
Q2. A 50-year-old female post-thyroidectomy reports new symptoms in the recovery room. The nurse assesses for hypocalcemia. Which findings SUGGEST HYPOCALCEMIA? Select all that apply.
- A. Chvostek sign (facial twitch with cheek tap) + Trousseau sign (carpal spasm with BP cuff)
- B. Hyperreflexia + tetany
- C. Decreased deep tendon reflexes (NOT hypoCa — feature of hyperCa or hypoMg)
- D. Numbness + tingling around mouth + fingers
- E. Constipation (NOT hypoCa — feature of hyperCa)
- F. QT prolongation on ECG
Show answer and rationale
Answer: Chvostek sign (facial twitch with cheek tap) + Trousseau sign (carpal spasm with BP cuff)Hyperreflexia + tetanyNumbness + tingling around mouth + fingersQT prolongation on ECG
Hypocalcemia: Chvostek + Trousseau + hyperreflexia + tetany + perioral/fingertip paresthesia + QT prolongation + seizures. Decreased DTRs and constipation are NOT hypoCa.
Q3. A 25-year-old female in the ED hyperventilating after a panic attack. ABG shows pH 7.50, PaCO2 30, HCO3 24. The ED nurse identifies the disturbance. The interpretation is:
- A. Metabolic acidosis (NOT — pH alkalotic)
- B. Acute respiratory alkalosis (pH alkalemia + PaCO2 low primary + HCO3 normal — no compensation yet)
- C. Compensated metabolic alkalosis (NOT — HCO3 not elevated)
- D. Normal (NOT — pH and PaCO2 abnormal)
Show answer and rationale
Answer: Acute respiratory alkalosis (pH alkalemia + PaCO2 low primary + HCO3 normal — no compensation yet)
Acute respiratory alkalosis: pH ↑ + PaCO2 ↓ (primary) + HCO3 normal (no metabolic compensation yet). Causes: hyperventilation (anxiety/panic, PE, salicylate toxicity, sepsis, fever, pain).
The rules that decide these questions
From the pack's rule cards — the reasoning shortcuts a wrong answer usually means you were missing.
HypoNa < 135: neuro symptoms (headache, confusion, seizure). Causes: SIADH (euvolemic, concentrated urine), hypovolemic, hypervolemic dilutional. Treatment: fluid restrict (SIADH), correct max 6-8 mEq/L per 24 hr to prevent ODS/CPM; hypertonic 3% for severe symptomatic. HyperNa > 145: thirst, dry, AMS. Causes: water loss (DI, GI), excess Na. Replace water deficit; max 10 mEq/L per 24 hr to prevent cerebral edema; DDAVP for central DI. RAPID CORRECTION = devastating CNS injury.
HypoK < 3.5: weakness, U waves, flattened T, dig toxicity. Replace via pump max 10-20 mEq/hr IV (NEVER PUSH — fatal); replace Mg concurrently. HyperK > 5.0 ECG: peaked T → wide QRS → sine wave → asystole. Treatment ORDER: (1) CALCIUM GLUCONATE IV (stabilize membrane, doesn't lower K); (2) INSULIN + D50 + ALBUTEROL (shift); (3) KAYEXALATE/FUROSEMIDE/DIALYSIS (eliminate). STOP K-sparing meds.
HypoCa < 8.5: tetany, perioral paresthesia, Chvostek + Trousseau, prolonged QT, laryngospasm. Causes: post-thyroidectomy, hypoparathyroidism, hypoMg, vit D def, pancreatitis. IV calcium gluconate slow + REPLACE Mg (Ca won't correct without Mg). HyperCa > 10.5: 'Bones, Stones, Groans, Moans' — lethargy, polyuria, stones, bone pain, shortened QT. HYDRATE FIRST aggressive IV NS + calcitonin + bisphosphonate; furosemide ONLY when euvolemic.
HypoMg < 1.7: tremor, tetany, torsades de pointes, refractory hypoK + hypoCa. IV MgSO4 1-2 g for severe; torsades = 2 g bolus. HyperMg > 2.6: hypotension, ↓ DTRs (areflexia 7-10), respiratory depression (RR 8-12), cardiac arrest > 15. Treatment: STOP Mg source + IV CALCIUM GLUCONATE (antidote) + furosemide + dialysis if AKI. Preeclampsia MgSO4 monitor: RR ≥ 12, DTRs present, UO ≥ 30 mL/hr, calcium gluconate at bedside.
HypoPhos < 2.5: weakness, respiratory failure, confusion, hemolysis. Refeeding syndrome in malnourished: insulin surge → drops phos, K, Mg → arrhythmia + death. PREVENT: thiamine 100 mg BEFORE feeding + start at 25-50% of goal + advance slowly + monitor electrolytes daily × 5-7 days. HyperPhos > 4.5 (CKD usually): dietary restrict + binders WITH MEALS (calcium carb/sevelamer/lanthanum) + dialysis. AVOID Mg/Al binders chronic.
Deficit: ↓ BP + ↑ HR + dry + ↓ UO + ↑ Hct + prerenal labs (BUN:Cr > 20). Excess: JVD + crackles + edema + weight gain + bounding pulse. Fluid choice: ISOTONIC (NS/LR — LR preferred trauma/burns) for hypovolemia; HYPOTONIC (1/2 NS, D5W) for free water deficit/hyperNa; HYPERTONIC (3% saline) for severe hypoNa/cerebral edema. Daily weight (same time/scale/clothing) = best fluid measure; 1 kg ≈ 1 L.
Practise the whole pack, tagged and explained
Every item carries its Client Needs category and clinical judgment step, so a wrong answer names the step that failed.
Frequently asked questions
How many Fluid, Electrolyte & Acid-Base questions does the bank have?
61 multiple-choice items, plus 10 unfolding cases in the Fluid, Electrolyte & Acid-Base pack, each with a rationale.
Are the samples real bank items?
Yes — the three questions above are drawn from the live bank, with their real rationales and tags.
Which clinical judgment steps does this topic train?
Most items in this topic test Analyze cues and Recognize cues, though every step appears.
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