Med-Surg · Renal / Fluid & Electrolytes
Fluid, Electrolytes & Acid-Base
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Prepared for Pass the Shift (owner: Kristina, RN). Always follow your facility’s protocols, provider orders, and current drug references.
1. Overview and Pathophysiology
Body water is distributed in intracellular and extracellular (intravascular + interstitial) compartments. Fluid moves by osmosis toward higher solute concentration. Nurses track volume (deficit vs excess) and composition (electrolytes and acid–base).
Fluid volume deficit ( / dehydration): losses (GI, skin, urine, bleeding) or inadequate intake → tachycardia, hypotension, dry mucosa, oliguria, weight loss.
Fluid volume excess (): HF, CKD, SIADH, excess IV fluids → weight gain, edema, , crackles, hypertension.
Acid–base: pH reflects hydrogen ion concentration. Lungs adjust PaCO₂ in minutes; kidneys adjust over hours to days. Use : Respiratory Opposite, Metabolic Equal.
2. Causes and Risk Factors
- Volume issues: vomiting/diarrhea, diuretics, burns, hemorrhage, heart/renal/liver failure, IV fluid overload
- Electrolyte shifts: GI losses, diuretics, CKD, endocrine disorders (SIADH, DI, hypo/hyperparathyroidism), cell lysis (TLS, rhabdomyolysis), alkalosis/acidosis
- Acid–base: COPD (respiratory acidosis), hyperventilation (respiratory alkalosis), DKA/lactic acidosis (metabolic acidosis), vomiting/NG suction (metabolic alkalosis)
3. Signs and Symptoms
| Imbalance | Classic cues |
|---|---|
| Hyponatremia | Headache, confusion, seizures, nausea; severe → cerebral edema |
| Hypernatremia | Thirst, dry mucosa, restlessness, seizures |
| Hypokalemia | Weakness, U waves, constipation, digoxin toxicity risk |
| Hyperkalemia | Peaked T waves, muscle weakness, bradydysrhythmias |
| Hypocalcemia | Tetany, [[chvostek |
| Hypercalcemia | “Bones, stones, groans, psychiatric overtones”; shortened QT |
| Hypomagnesemia | Tremors, torsades risk, often with low K⁺/Ca²⁺ |
| Metabolic acidosis | Kussmaul respirations, low HCO₃⁻, low pH |
| Metabolic alkalosis | Slow respirations, high HCO₃⁻, often from vomiting |
4. Diagnostics and Labs
Lab reference ranges vary by laboratory. Always use your facility’s ranges.
| Test | Typical adult range | Nursing relevance |
|---|---|---|
| Sodium | 135–145 mEq/L | Neuro status; correct slowly |
| Potassium | 3.5–5.0 mEq/L | Cardiac monitor for extremes |
| Calcium (total) | ~9.0–10.5 mg/dL | Correct for low albumin or use ionized Ca²⁺ |
| Magnesium | ~1.5–2.5 mEq/L (~1.7–2.2 mg/dL) | Dysrhythmias, neuromuscular |
| Phosphorus | ~3.0–4.5 mg/dL | Inverse relationship with calcium |
| BUN / Creatinine | ~10–20 / 0.6–1.2 mg/dL | Perfusion and renal function |
| Serum osmolality | ~285–295 mOsm/kg | Tonicity |
| Urine specific gravity | ~1.005–1.030 | Concentrating ability |
| ABG pH / PaCO₂ / HCO₃⁻ | 7.35–7.45 / 35–45 / 22–26 | Acid–base primary process + compensation |
5. Priority Nursing Assessments
- Daily weight (same conditions), I&O, orthostatic BP
- Telemetry when K⁺, Mg²⁺, or Ca²⁺ are abnormal
- Neurologic checks with Na⁺ disorders (seizure precautions if severe)
- Mucosa, skin turgor (less reliable in older adults), edema grade, lung sounds
- IV site and fluid type/rate; digoxin status if K⁺ low
- ABG trends and respiratory pattern
6. Priority Nursing Interventions
- Hypovolemia: oral/IV fluids as ordered; treat cause; fall precautions
- Hypervolemia: fluid/sodium restriction per order, diuretics, elevate HOB if pulmonary edema, daily weights
- Hyperkalemia: cardiac monitor; anticipate calcium gluconate (membrane protection), insulin + dextrose, beta-agonists, binders, dialysis—follow protocol order
- Hypokalemia: oral or IV K⁺ replacement—never IV push; dilute and infuse at controlled rate on a pump; monitor site for phlebitis
- Sodium disorders: correct gradually (risk of osmotic demyelination if chronic hyponatremia corrected too fast; cerebral edema if hypernatremia corrected too fast)
- Hypocalcemia: seizure/airway precautions; calcium replacement; check Mg²⁺
- Teach: salt substitutes often contain K⁺; report muscle weakness or palpitations
7. Medications
| Class / examples | Role | Nursing considerations |
|---|---|---|
| Isotonic crystalloids (0.9% NaCl, LR) | Volume expansion | Watch for overload |
| Hypotonic (0.45% NaCl) | Cellular rehydration | Neuro checks; avoid in ICP risk |
| Hypertonic (3% NaCl) | Severe symptomatic hyponatremia | ICU-level monitoring; central line often preferred |
| Loop/thiazide diuretics | Remove volume | K⁺/Mg²⁺ losses |
| Potassium chloride | Replace K⁺ | Pump only; max rates per policy; never IVP |
| Calcium gluconate / chloride | Protect heart or replace Ca²⁺ | Chloride is more concentrated—know which you have |
| Sodium polystyrene / patiromer / SZC | K⁺ binders | Onset not immediate for emergencies |
| Sodium bicarbonate | Selected metabolic acidosis | Not routine for all acidosis |
8. Patient Education
- Weigh daily if prone to fluid shifts; report rapid gains/losses
- Diet teaching matched to imbalance (low K⁺ in hyperkalemia; not unrestricted bananas during hyperkalemia treatment)
- Medication adherence (diuretics in morning)
- Oral fluid plans when restricted or encouraged
- Call for confusion, seizures, severe weakness, chest palpitations
9. Complications
- Dysrhythmias / cardiac arrest (especially K⁺ and Mg²⁺)
- Seizures / cerebral edema (Na⁺ extremes)
- Pulmonary edema from rapid fluid resuscitation
- Osmotic demyelination from overly rapid Na⁺ correction
- Laryngospasm from severe hypocalcemia
10. Memory Aids
- “ROME”: Respiratory Opposite, Metabolic Equal
- “Peaks = potassium high; U waves = potassium low”
- “Ca and Phos see-saw”
- “IV potassium: dilute, pump, never push”
- “1 kg ≈ 1 L fluid”
11. NCLEX-Style Practice Questions
1. A client with CKD has K⁺ 6.8 mEq/L and peaked T waves. First action?
A. Give a banana smoothie
B. Place on continuous cardiac monitoring and notify the provider
C. Encourage oral fluids only
D. Schedule dialysis for next week and discharge teaching
Answer: B. Severe hyperkalemia with ECG changes can become lethal quickly—monitor and escalate while anticipating emergency treatment.
2. Which ABG shows uncompensated metabolic acidosis?
A. pH 7.28, PaCO₂ 40, HCO₃⁻ 16
B. pH 7.50, PaCO₂ 28, HCO₃⁻ 22
C. pH 7.36, PaCO₂ 60, HCO₃⁻ 34
D. pH 7.44, PaCO₂ 32, HCO₃⁻ 20
Answer: A. Low pH + low HCO₃⁻ with normal PaCO₂ = uncompensated metabolic acidosis.
3. The nurse is preparing IV potassium chloride for K⁺ 2.9 mEq/L. Which action is appropriate?
A. Push 10 mEq IV over 1 minute
B. Dilute as ordered and infuse via pump at policy rate
C. Add undiluted KCl to a running IV bag at the bedside without checking rate
D. Give IM potassium
Answer: B. Potassium is never given IV push; use diluted infusions on a pump within facility rate limits.
4. Positive Chvostek and Trousseau signs suggest which imbalance?
A. Hyperkalemia
B. Hypocalcemia
C. Hypernatremia
D. Fluid volume excess
Answer: B. Neuromuscular excitability is classic for low calcium (often also check magnesium).
5. Why must chronic severe hyponatremia be corrected slowly?
A. To avoid osmotic demyelination syndrome
B. To raise blood glucose
C. To prevent hyperkalemia only
D. Because sodium must stay below 120 forever
Answer: A. Overly rapid correction of chronic hyponatremia can cause osmotic demyelination; follow specialist/protocol targets.
References
MedlinePlus. (n.d.). Fluid and electrolyte balance. National Library of Medicine. Retrieved October 15, 2026, from https://medlineplus.gov/fluidandelectrolytebalance.html
MedlinePlus. (n.d.). Acid-base balance. National Library of Medicine. Retrieved October 15, 2026, from https://medlineplus.gov/ency/article/001181.htm
National Council of State Boards of Nursing. (2026). 2026 NCLEX-RN test plan. https://www.nclex.com/test-plans.page
Hopkins, E., Sanvictores, T., & Sharma, S. (2022). Physiology, acid base balance. In StatPearls. StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK507807/
Rondon, H., & Badireddy, M. (2023). Hyponatremia. In StatPearls. StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK470386/