Fluid and Electrolytes Nursing Guide 2026: Imbalances, IV Fluids, and Treatment
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Fluid Volume Disorders
| Disorder | Causes | Signs & Symptoms | Treatment |
|---|
| Fluid Volume Deficit (FVD) / Hypovolemia | Vomiting, diarrhea, excessive diaphoresis, hemorrhage, burns, inadequate intake, DI, hyperglycemia, diuretics | Decreased BP, increased HR, orthostatic hypotension, decreased urine output (<30 mL/hr), increased urine specific gravity (>1.030), dry mucous membranes, decreased skin turgor (tenting), thirst, flat neck veins, concentrated urine, weight loss | IV fluid replacement (isotonic NS or LR); oral fluids if tolerated; identify and treat cause; blood products if hemorrhagic; monitor I&O hourly |
| Fluid Volume Excess (FVE) / Hypervolemia | Excessive IV fluids, CHF, renal failure, cirrhosis, SIADH, hypoalbuminemia, excessive sodium intake | HTN, bounding pulse, increased CVP, edema (pitting peripheral, sacral in bedbound), crackles in lungs, dyspnea, JVD, S3 heart sound, weight gain, dilutional hyponatremia, frothy/pink sputum | Fluid restriction; sodium restriction; diuretics (furosemide); elevate HOB; monitor daily weights; assess lung sounds; I&O; dialysis if severe renal failure |
Daily weight is the most accurate measure of fluid balance: 1 kg weight gain = ~1 liter of fluid retained. Weigh at the same time each day (usually morning, before breakfast, after voiding) with same scale and same clothing.
IV Fluid Types: Isotonic, Hypotonic, Hypertonic
| Type | Osmolality | Effect | Examples | Uses |
|---|
| Isotonic | ~280–300 mOsm/kg (same as plasma) | Expands ECF (intravascular and interstitial space); does NOT shift into cells; stays in vascular space | 0.9% NS (normal saline), Lactated Ringer's (LR), 5% Dextrose in Water (D5W) — isotonic in bag, becomes hypotonic once dextrose metabolized | Hypovolemia, resuscitation, blood transfusion (NS only), pre-/post-op hydration; LR: burns, trauma, surgery |
| Hypotonic | <280 mOsm/kg (less than plasma) | Shifts water INTO cells; dilutes serum; expands intracellular space; SHRINKS vascular volume | 0.45% NS (half normal saline), 0.33% NS, D5W (after metabolism) | Cellular dehydration (hyperosmolar states, DKA after initial resuscitation, cellular rehydration); CAUTION: can cause fluid overload, increased ICP in head injury, cell swelling |
| Hypertonic | >300 mOsm/kg (more than plasma) | Draws water OUT of cells into bloodstream; shrinks cells; expands intravascular space | 3% NS, 5% NS, D10W, D50W, D5 0.9% NS, D5LR, 7.5% NS, Albumin 25% | Severe symptomatic hyponatremia (3% NS); increased ICP (pulls water from brain cells); DKA (D50W for hypoglycemia); CAUTION: peripheral vein irritation; must be given slowly or via central line |
3% Normal Saline (hypertonic saline) for severe hyponatremia must be given SLOWLY (correct Na by no more than 8–10 mEq/L per 24 hr) to prevent osmotic demyelination syndrome (central pontine myelinolysis) — irreversible brain injury from too-rapid sodium correction.
Sodium (Normal: 135–145 mEq/L)
| Hyponatremia (<135) | Hypernatremia (>145) |
|---|
| Common Causes | SIADH (most common), heart failure, cirrhosis, renal failure, excessive hypotonic fluid, psychogenic polydipsia, adrenal insufficiency, vomiting, diuretics | Inadequate water intake (elderly, unconscious), diabetes insipidus (central or nephrogenic), diarrhea, diaphoresis, fever, nasogastric fluid losses without replacement |
| Symptoms | Headache, nausea, confusion, lethargy, seizures, coma (severe <120); MENTAL STATUS CHANGES early | Thirst, restlessness, irritability, dry mucous membranes, elevated temp, tachycardia; NEUROLOGIC symptoms (agitation, seizures, coma) in severe cases |
| Treatment | Fluid restriction (SIADH); isotonic or hypertonic saline (symptomatic); treat underlying cause; demeclocycline for chronic SIADH; correct SLOWLY (≤8–10 mEq/L per 24 hr) | Gradual rehydration with hypotonic fluids (0.45% NS or oral water); correct SLOWLY (≤10–12 mEq/L per 24 hr); rapid correction → cerebral edema |
Potassium (Normal: 3.5–5.0 mEq/L)
Potassium is the PRIMARY intracellular cation. Even small changes affect cardiac and neuromuscular function.
| Hypokalemia (<3.5) | Hyperkalemia (>5.0) |
|---|
| Common Causes | Loop diuretics (furosemide), vomiting/diarrhea/NG suction, poor intake, insulin + glucose, alkalosis (K+ shifts into cells), excessive sweating | Renal failure (most common), acidosis (K+ shifts out of cells), potassium-sparing diuretics (spironolactone), ACE inhibitors/ARBs, tissue destruction (rhabdomyolysis, burns, tumor lysis syndrome), excessive K+ supplements |
| Cardiac Effects | EKG: flattened T waves, U waves (HALLMARK), widened QRS, ST depression; ventricular dysrhythmias; digoxin toxicity worsened (low K+ enhances digoxin toxicity) | EKG: peaked (tall, narrow, tented) T waves (FIRST CHANGE), widened QRS, sine-wave pattern, ventricular fibrillation, asystole; LIFE-THREATENING cardiac arrhythmias |
| Neuromuscular | Muscle weakness, cramps, fatigue; paralytic ileus (bowel sounds absent); constipation; respiratory muscle weakness (severe) | Muscle weakness, paralysis; ascending (unlike Guillain-Barré which is also ascending); paresthesias; cramping |
| Treatment | KCl replacement PO or IV; NEVER IV push (causes cardiac arrest); IV KCl max 10–20 mEq/hr via pump; always on continuous cardiac monitor during IV K+ replacement; replace magnesium (low Mg causes refractory hypokalemia) | Calcium gluconate (cardiac membrane stabilization — FASTEST, not definitive); insulin + D50W (drives K+ into cells); sodium bicarbonate; sodium polystyrene (Kayexalate) or patiromer (eliminate K+); dialysis (definitive for renal failure); monitor EKG |
IV potassium NEVER given by IV push — ALWAYS diluted and infused via pump with cardiac monitoring. Max rate 10–20 mEq/hr peripheral vein (10 mEq/hr standard; 20 mEq/hr only with continuous cardiac monitoring). Peripheral concentration limits vary by facility — commonly 10 mEq/100 mL (0.1 mEq/mL), and many protocols cap peripheral potassium at 40 mEq/L; check your policy. A central line is required for faster rates or more concentrated potassium: 40 mEq/100 mL is a central, critical-care concentration, never peripheral.
Calcium (Normal: 8.5–10.5 mg/dL; Ionized: 1.12–1.32 mmol/L)
| Hypocalcemia (<8.5) | Hypercalcemia (>10.5) |
|---|
| Common Causes | Hypoparathyroidism (post-thyroidectomy!), vitamin D deficiency, renal failure (impaired vitamin D activation), pancreatitis, malabsorption, large blood transfusions (citrate chelates Ca), hypomagnesemia | Hyperparathyroidism (most common outpatient), malignancy (PTHrP secretion), prolonged immobility, thiazide diuretics, vitamin D toxicity, milk-alkali syndrome, Paget disease |
| Symptoms | Trousseau sign (BP cuff inflates → carpopedal spasm), Chvostek sign (tap facial nerve → facial twitching), tetany, muscle cramps, perioral numbness/tingling, seizures, laryngospasm, prolonged QT (EKG) | "Stones, bones, groans, and psychic moans": kidney stones, bone pain, GI (nausea/constipation), confusion/depression; hyporeflexia; shortened QT on EKG; polyuria/polydipsia |
| Treatment | Calcium gluconate IV (safer, less tissue necrosis than calcium chloride) for symptomatic/acute; calcium carbonate PO for mild/chronic; vitamin D supplementation; magnesium replacement if hypomagnesemia present | IV normal saline hydration (FIRST); furosemide (loop diuretic promotes Ca excretion); bisphosphonates (pamidronate, zoledronic acid) for malignancy-related; calcitonin; treat underlying cause; dialysis if severe |
Magnesium (Normal: 1.5–2.5 mg/dL)
| Hypomagnesemia (<1.5) | Hypermagnesemia (>2.5) |
|---|
| Causes | Alcoholism (most common cause), diarrhea, malabsorption, diuretics, DKA, PPI use (chronic) | Renal failure (most common), excessive Mg supplements, antacid overuse (Mg-containing), eclampsia treatment (Mg toxicity) |
| Symptoms | Tremors, muscle cramps, hyperreflexia, hypokalemia and hypocalcemia (REFRACTORY — cannot correct K or Ca without replacing Mg), tetany, torsades de pointes (prolonged QT), confusion, seizures | LOSS of deep tendon reflexes (FIRST SIGN), bradycardia, hypotension, respiratory depression, cardiac arrest, nausea/flushing; Mg >7: respiratory arrest; Mg >12: cardiac arrest |
| Treatment | IV or PO magnesium sulfate; IV for symptomatic/severe | STOP all Mg; calcium gluconate IV (antidote for life-threatening toxicity); forced diuresis with NS + furosemide; dialysis if severe renal failure |
Magnesium toxicity monitoring mnemonic: Check DEEP TENDON REFLEXES (patellar reflex) before each Mg dose — loss of DTRs is the first sign of toxicity. If DTRs are absent: HOLD Mg, give calcium gluconate. Also monitor RR ≥12 and urine output ≥30 mL/hr.
Phosphorus (Normal: 2.5–4.5 mg/dL)
| Hypophosphatemia (<2.5) | Hyperphosphatemia (>4.5) |
|---|
| Causes | Refeeding syndrome (CRITICAL — insulin drives phosphate into cells when nutrition restarted after starvation), alcoholism, malabsorption, antacid overuse (phosphate binders), DKA treatment, hyperparathyroidism | Renal failure (most common), hypoparathyroidism, excessive phosphate intake, tumor lysis syndrome, rhabdomyolysis, vitamin D toxicity |
| Symptoms | Muscle weakness, fatigue, respiratory failure (severe <1.0), hemolytic anemia, confusion, bone pain; impairs 2,3-DPG (hemoglobin releases less O2 to tissues) | Hypocalcemia symptoms (Ca-phosphate precipitation), calcification of soft tissues, itching; renal osteodystrophy in chronic |
| Treatment | Oral phosphate replacement preferred; IV sodium or potassium phosphate for severe (<1.0); monitor for refeeding syndrome in malnourished patients starting nutrition | Phosphate-binding medications (calcium carbonate, sevelamer) with meals; dietary phosphate restriction; dialysis for renal failure; treat hypocalcemia |
NCLEX High-Yield Points
- Daily weight is the BEST measure of fluid balance; 1 kg change = 1 liter fluid
- Isotonic fluids: NS, LR — stay in vascular space; for hypovolemia. Hypotonic: 0.45%NS — goes into cells. Hypertonic: 3%NS, D50 — pulls fluid from cells
- Correct Na SLOWLY: no more than 8–10 mEq/L per 24 hr in either direction (too fast = osmotic demyelination or cerebral edema)
- IV K+ NEVER by IV push; max 10–20 mEq/hr; diluted; cardiac monitor required
- Low K+ + EKG: U wave is hallmark. High K+ + EKG: peaked T waves first, then widened QRS, then VFib
- Calcium gluconate stabilizes the heart in hyperkalemia (temporary); insulin + D50 shifts K+ into cells
- Low Ca: Trousseau sign (carpopedal spasm with BP cuff), Chvostek sign (facial twitch with tap)
- Mg toxicity: FIRST sign = loss of deep tendon reflexes; antidote = calcium gluconate
- Refeeding syndrome: hypophosphatemia is the most dangerous electrolyte shift when restarting nutrition in severely malnourished patients
- Hypomagnesemia causes REFRACTORY hypokalemia and hypocalcemia — always check and replace Mg
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