NCLEX-RN — Fluids & Electrolytes flashcards
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Hypo and hyper states for sodium, potassium, calcium, magnesium, and phosphate with their causes, bedside signs, ECG changes, and nursing priorities; isotonic, hypotonic, and hypertonic IV fluids; fluid deficit versus excess; and SIADH versus diabetes insipidus.
Learn deck · part of NCLEX-RN · written against: NCSBN 2026 NCLEX-RN Test Plan, in effect from 1 April 2026 (Next Generation NCLEX; client-needs categories and percentages unchanged from 2023, fact-checked 2026-10-11). Updated 2026-10-10.
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Which signs tell the nurse a client has fluid volume deficit (hypovolemia)?Think 'dry and fast': tachycardia with a thready pulse, orthostatic hypotension, flat neck veins, dry mucous membranes with poor turgor, and low, concentrated urine output; the hematocrit and BUN rise from hemoconcentration. The pulse climbs before the pressure falls, and weight loss is the most reliable gauge.Fluid Balance
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Which signs tell the nurse a client has fluid volume excess (hypervolemia)?Think 'wet and heavy': bounding pulse, hypertension, distended neck veins, crackles and dyspnea, dependent edema, and rapid weight gain; the hematocrit and BUN fall from dilution. Daily weight is the most sensitive indicator — a gain of 1 kg is about 1 liter of retained fluid.Fluid Balance
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Which IV fluids are isotonic, and where does the fluid go once infused?0.9% sodium chloride (normal saline), lactated Ringer's, and 5% dextrose in water while it is in the bag (D5W turns hypotonic once the dextrose is metabolized). Isotonic fluid stays in the vascular space, expanding circulating volume without pulling water into or out of cells.IV Fluids
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What are the common causes of hyponatremia the NCLEX tests?Water excess or sodium loss: SIADH, heart failure and cirrhosis (dilution), thiazide diuretics, vomiting and diarrhea replaced with plain water, excessive hypotonic IV fluid, psychogenic polydipsia, and adrenal insufficiency. Ask what the client has been drinking and which diuretic they take.Sodium
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What are the common causes of hypokalemia?GI loss (vomiting, diarrhea, NG suction, laxative abuse), renal loss (loop and thiazide diuretics, corticosteroids, hyperaldosteronism), and shift into cells (insulin, alkalosis, beta-2 agonists). Poor intake adds to it in alcohol-use disorder and eating disorders.Potassium
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What are the common causes of hypocalcemia?Hypoparathyroidism after thyroid or parathyroid surgery, vitamin D deficiency, chronic kidney disease, acute pancreatitis, low magnesium, loop diuretics, and massive transfusion of citrated blood, which binds calcium.Calcium
Watch out: with a low albumin the total calcium reads low while the active ionized calcium may be normal, so check an ionized or corrected value before treating. -
What are the common causes of hypomagnesemia?Alcohol-use disorder is the classic one; add malnutrition and malabsorption, chronic diarrhea, loop and thiazide diuretics, long-term proton pump inhibitors, and the treatment phase of DKA. It often coexists with low potassium and low calcium.Magnesium
Watch out: low potassium will not correct until the magnesium is replaced, so check magnesium when potassium stays low despite replacement. -
What causes hypophosphatemia, and why does it matter?Refeeding syndrome in a malnourished client, insulin treatment of DKA, alcohol-use disorder, chronic use of aluminum antacids, and respiratory alkalosis. Phosphate is needed for ATP, so the client becomes weak and confused and can develop respiratory failure and hemolysis.Phosphate
Why: in refeeding, the insulin surge drives phosphate into cells to make ATP for the incoming glucose. -
What goes wrong in SIADH, and what does the nurse see in the labs?Too much antidiuretic hormone makes the kidneys retain water: the client has dilutional hyponatremia with a low serum osmolality, yet the urine is concentrated with a high specific gravity and low output. Causes include small-cell lung cancer, head injury, and drugs such as SSRIs and carbamazepine.SIADH & Diabetes Insipidus
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How do potassium and acid-base status affect each other?In acidosis, hydrogen ions move into cells and push potassium out, raising the serum potassium; in alkalosis the reverse lowers it. So correcting DKA with insulin and fluids can unmask a dangerous hypokalemia, and treating acidosis with bicarbonate lowers potassium.Acid-Base Links
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About these cards
Review status: Second-reader reviewed, with corrections applied.
Checked against:
- Checked against Open RN Nursing Fundamentals, chapter on fluids and electrolytes (Chippewa Valley Technical College, CC BY 4.0); reference only, no text copied.
- OpenStax Anatomy and Physiology 2e, chapter on fluid, electrolyte, and acid-base balance, consulted as a reference; no text copied.
- Treatment principles cross-checked against MedlinePlus (U.S. National Library of Medicine); reference only.
- IV-site complications, colloids and orthostatic vital signs checked against Open RN Nursing Skills (Chippewa Valley Technical College, CC BY 4.0); DKA fluid and insulin principles against the 2024 ADA/EASD consensus report on hyperglycemic crises in adults; reference only, no text copied.
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