Fluid & Electrolyte Disorders — Core Concepts

Fluid and electrolyte balance forms the physiologic foundation for perfusion, cardiac rhythm, and homeostasis. Even small shifts in water or ions alter cell excitability and acid–base equilibrium.Nurses interpret subtle changes in I&O, lab trends, and patient presentation to prevent complications ranging from hypovolemic shock to arrhythmias.

Safety anchors:

• Monitor I&O, daily weights, vitals, neuro & cardiac signs

• Trend serum electrolytes (Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl⁻, PO₄³⁻)

• Use infusion pumps for all hypertonic or potassium-containing IVs

• Reassess fluid therapy frequently in older adults and renal/hepatic patients

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Clinical judgment:Pattern → loss, retention, or shift?Priority → stabilize circulation, correct cause, prevent recurrence.

Use this pack to:

• Scan high-yield tables

• Memorize hallmark findings

• Apply fluid principles clinically

• Practice NGN-style reasoning for safe interventions.

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⚗️ 1) Fluid Balance Disorders

Conceptual Focus

Fluid homeostasis depends on intake, renal output, ADH, aldosterone, and capillary dynamics.Nurses interpret changes in weight, urine output, mucosa, BP, and osmolality to identify imbalances early.

Clinical Judgment Focus

• Evaluate volume status: look for tissue perfusion changes, not just numbers.

• Identify cause: renal vs. extrarenal loss, hormonal, third-spacing.

• Implement safe correction: isotonic for deficit, restriction/diuretics for excess.

Disorder	Causes / Risk Factors	Diagnostic Findings / Labs	Nursing Management / Interventions
Fluid Volume Deficit (FVD) (Hypovolemia, Dehydration)	Vomiting, diarrhea, hemorrhage, fever, burns, diuretics, NPO, third spacing	↓ BP, ↑ HR, weak pulses, poor turgor, dry mucosa, ↑ Hct, ↑ BUN, ↑ urine specific gravity	Replace fluids (oral/IV isotonic NS or LR), monitor I&O & weights, assess orthostatic BP, treat underlying cause, watch for hypovolemic shock
Fluid Volume Excess (FVE) (Hypervolemia, Overload)	Heart failure, renal failure, SIADH, corticosteroids, excess IV fluids	↑ BP, bounding pulses, crackles, edema, ↓ Hct, ↓ BUN, pulmonary congestion	Restrict Na⁺/fluids, give diuretics, elevate HOB, monitor lungs, daily weights, evaluate response to therapy
Third-Spacing (Fluid Shift)	Burns, sepsis, hypoalbuminemia, post-op stress	Edema, ↓ BP, ↓ UO despite normal intake, ↑ weight	Correct cause, albumin or colloid therapy, monitor perfusion, assess for fluid mobilization phase
SIADH (Syndrome of Inappropriate ADH)	CNS lesions, head trauma, lung cancer, SSRIs, carbamazepine	↓ Na⁺, ↓ osmolality, concentrated urine, weight gain	Fluid restriction, hypertonic saline via pump, seizure precautions, monitor neurostatus, treat cause
Diabetes Insipidus (DI)	↓ ADH (neurogenic) or renal unresponsiveness (nephrogenic)	Polyuria, polydipsia, ↑ Na⁺, ↑ osmolality, ↓ urine specific gravity	Administer desmopressin (DDAVP), monitor Na⁺ and osmolality, encourage fluids, assess hydration

Acid–Base Connection:FVD → metabolic acidosis risk (poor perfusion/lactic acid)FVE → possible respiratory alkalosis (pulmonary congestion)

Memory Aid — F.L.U.I.D.S.Find cause • Labs trend • Urine check • Intake/output • Daily weight • Safety first

🧂 2) Sodium (Na⁺) Imbalances

Normal: 135–145 mEq/LControls water distribution and nerve conduction. Closely linked to ADH and osmolality.

Disorder	Causes / Risk Factors	Diagnostics / Labs	Nursing Management / Interventions
Hyponatremia (<135)	SIADH, diuretics, GI losses, CHF, renal failure, excess hypotonic fluids	↓ Na⁺, ↓ osmolality, confusion, seizures, edema	Fluid restriction, isotonic or hypertonic (3%) saline via pump, seizure precautions, monitor neurostatus
Hypernatremia (>145)	Water deprivation, DI, hypertonic feedings, excessive Na⁺ intake	↑ Na⁺, ↑ osmolality, dry mucosa, thirst, restlessness	Gradual rehydration (D5W or 0.45% NS), monitor Na⁺ and neuro signs, avoid rapid correction

Memory Aid — S.A.L.T.Skin flushed • Agitation • Low-grade fever • Thirst

Special Nursing Focus:Rapid Na⁺ correction → central pontine myelinolysis risk (never >10–12 mEq/L per 24 hr).

⚡ 3) Potassium (K⁺) Imbalances

Normal: 3.5–5.0 mEq/LPrimary intracellular cation essential for neuromuscular and cardiac activity.Directly influenced by acid–base balance and renal excretion.

Disorder	Causes / Risk Factors	Diagnostics / Labs	Nursing Management / Interventions
Hypokalemia (<3.5)	Diuretics, vomiting, diarrhea, NG suction, steroids, alkalosis	Flat T/U waves, weakness, ↑ digoxin toxicity	Administer oral/IV K⁺ (≤10 mEq/hr), ECG monitor, high-K⁺ foods, assess Mg²⁺ (low Mg = low K)
Hyperkalemia (>5.0)	Renal failure, K⁺-sparing diuretics, acidosis, trauma, transfusion	Peaked T waves, wide QRS, bradycardia	Stop K⁺ sources, give Ca gluconate, insulin + D50, sodium bicarb, Kayexalate, dialysis if severe

Memory Aids:

• K+ killers: ACEI, ARBs, spironolactone

• Low K+ = low Mg²⁺ correction first!

• K.I.D.N.E.Y. = Keep ECG • Investigate cause • Don’t push KCl • Note diet • Evaluate muscles • Yield nephrotoxins

🦴 4) Calcium (Ca²⁺) Imbalances

Normal: 8.5–10.5 mg/dLVital for bones, clotting, nerve transmission, and muscle tone.

Disorder	Causes / Risk Factors	Diagnostics / Labs	Nursing Management / Interventions
Hypocalcemia (<8.5)	Hypoparathyroidism, vit D deficiency, pancreatitis, renal failure	+Chvostek, +Trousseau, tetany, prolonged QT	Administer Ca gluconate, vit D, seizure precautions, monitor airway and ECG
Hypercalcemia (>10.5)	Hyperparathyroidism, malignancy, immobility	Short QT, weakness, kidney stones	IV fluids (3–4 L/day), loop diuretics, calcitonin, mobility, avoid Ca foods/supplements

Memory Aids:C.A.L.C.I.U.M. — Cramps low, Arrhythmia, Loop diuretics, Calcitonin, IV fluids, Urine flush, Monitor ECGInverse relation: Ca²⁺ ↓ → PO₄³⁻ ↑

🧲 5) Magnesium (Mg²⁺) Imbalances

Normal: 1.3–2.1 mEq/LStabilizes cardiac rhythm and neuromuscular excitability.

Disorder	Causes / Risk Factors	Diagnostics / Labs	Nursing Management / Interventions
Hypomagnesemia (<1.3)	Alcoholism, malabsorption, diuretics, DKA	Tremors, ↑ DTRs, seizures, dysrhythmias	IV MgSO₄ (slow), monitor DTRs and RR, seizure precautions, Mg-rich foods
Hypermagnesemia (>2.1)	Renal failure, antacids/laxatives	↓ DTR, hypotension, bradycardia	Stop Mg, give Ca gluconate, support airway, dialysis if severe

Memory Aid — M.A.G.Monitor DTRs • Airway support • Gluconate if high

🧪 6) Chloride (Cl⁻) Imbalances

Normal: 98–106 mEq/LTracks with sodium; influences acid–base balance (forms HCl).

Disorder	Causes / Risk Factors	Diagnostics / Labs	Nursing Management / Interventions
Hypochloremia (<98)	Vomiting, NG suction, metabolic alkalosis	↓ Cl⁻, shallow breathing	Replace with NS, correct alkalosis
Hyperchloremia (>106)	Dehydration, metabolic acidosis, NS overload	Kussmaul respirations, weakness	Correct acidosis, switch fluids, monitor ABG

🧫 7) Phosphate (PO₄³⁻) Imbalances

Normal: 2.5–4.5 mg/dLInterlinked with calcium metabolism; key in ATP and bone structure.

Disorder	Causes / Risk Factors	Diagnostics / Labs	Nursing Management / Interventions
Hypophosphatemia (<2.5)	Malnutrition, alcoholism, DKA recovery	Weakness, ↓ reflexes	Replace phosphate (oral/IV), monitor Ca²⁺
Hyperphosphatemia (>4.5)	CKD, hypoparathyroidism, tumor lysis	Tetany, calcification	Phosphate binders (sevelamer), low-PO₄ diet, dialysis

🧠 Quick Checks (Retrieval)

1️⃣ Identify a fluid balance disorder with low urine output but rising weight.2️⃣ What Na⁺ level and symptom combination indicates severe hyponatremia?3️⃣ Which electrolyte imbalance shows prolonged QT?4️⃣ How fast can IV K⁺ be infused safely?5️⃣ A patient on furosemide and digoxin presents with muscle weakness — which imbalance do you suspect?

Answers:

1. SIADH or third-spacing

2. Na⁺ <120 + seizures/confusion

3. Hypocalcemia

4. ≤10 mEq/hr via pump

5. Hypokalemia

🧩 NGN-Style Mini-Item #1

Scenario:An elderly client presents with diarrhea for 4 days, BP 88/56, HR 122, dry tongue, and Na⁺ 150 mEq/L.

Select all that apply:☐ Start NS bolus rapidly☐ Monitor daily weight☐ Start hypotonic IV after initial stabilization☐ Restrict fluids☐ Assess for confusion and seizures

Correct: ✅ NS bolus → stabilize • ✅ Daily weight • ✅ Hypotonic IV (gradual correction) • ✅ Monitor neurostatusWhy: Restore volume first, then correct Na⁺ slowly to prevent cerebral edema.

🧩 NGN-Style Mini-Item #2

Scenario:A patient on hemodialysis presents with peaked T-waves and K⁺ 6.8 mEq/L.

Priority actions:☐ Administer Ca gluconate IV☐ Give insulin with D50☐ Restrict oral K⁺ foods☐ Prepare for dialysis☐ Push IV KCl for muscle weakness

Correct: ✅ Ca gluconate • ✅ Insulin/D50 • ✅ Prepare dialysis • ✅ Restrict K⁺Rationale: Protect myocardium first, shift K⁺ intracellularly, then remove it.

✨ Closing Practice Pearls

• 1 kg = 1 L fluid. Daily weight is the most sensitive volume indicator.

• Correct slowly. Rapid shifts cause brain or cardiac injury.

• Trends > snapshots. Look for progressive lab or clinical changes.

• Pairings: Na⁺↔Cl⁻, Ca²⁺↔Phosphate, Mg²⁺↔K⁺.

• Cardiac trio: K⁺, Ca²⁺, Mg²⁺ control rhythm stability.

• Old rule still true: “If urine output falls, listen to the lungs before you push fluids.”

• Educate: hydration cues, diet (Na⁺, K⁺, Mg²⁺), medication side effects, when to seek care.