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Fluid and Electrolyte Imbalances

Sep 19, 2025

Overview

This lecture covers the main fluid and electrolyte imbalances nurses must know, including their causes, signs and symptoms, and relevant lab values.

Fluid and Electrolyte Basics

  • Body fluids and electrolytes must remain in balance for proper cellular and organ function.
  • Electrolytes are ions in blood and body fluids that help with nerve signaling, muscle contraction, and acid-base balance.
  • Major electrolytes: sodium, chloride, potassium, calcium, magnesium, phosphate.
  • Kidneys and gastrointestinal tract regulate electrolyte levels; renal or GI dysfunction affects balance.

Sodium (Na+)

  • Normal: 135–145 mEq/L; mainly extracellular.
  • Hyponatremia (<135): causes include diuretics, GI loss, Addison’s disease, SIADH, fluid overload.
  • Signs of hyponatremia: SALT LOSS (seizures, abdominal cramps, lethargy, diminished reflexes, etc.).
  • Hypernatremia (>145): causes include Cushing’s, Conn’s syndrome, dehydration, diabetes insipidus, excessive intake.
  • Signs of hypernatremia: NO FRIED FOOD (fatigue, restlessness, increased reflexes, extreme thirst, dry mouth, low urine).

Chloride (Cl-)

  • Normal: 95–105 mEq/L; parallels sodium.
  • Hypochloremia: causes include GI loss, diuretics, burns, heart failure, SIADH, metabolic alkalosis.
  • Signs: similar to hyponatremia; dehydration, low BP, lethargy.
  • Hyperchloremia: causes include excess sodium, dehydration, decreased bicarb, Conn’s, corticosteroids, metabolic acidosis.
  • Signs: similar to hypernatremia and acidosis.

Potassium (K+)

  • Normal: 3.5–5 mEq/L; mainly intracellular.
  • Hypokalemia (<3.5): caused by loop diuretics, corticosteroids, insulin, GI loss, Cushing’s, starvation.
  • Signs: Seven L’s (lethargy, low respirations, lethal arrhythmias, lots of urine, leg cramps, limp muscles, low BP/HR).
  • Hyperkalemia (>5): caused by burns, rhabdomyolysis, Addison’s, renal failure, potassium-sparing diuretics, ACE inhibitors.
  • Signs: MURDER (muscle weakness, urinary low, respiratory failure, decreased contractility, early twitch/cramp, rhythm changes).

Calcium (Ca2+)

  • Normal: 8.5–10.5 mg/dL; bone/teeth health, nerve/muscle, clotting.
  • Regulated by vitamin D, parathyroid hormone (PTH), and calcitonin.
  • Hypocalcemia: caused by low PTH (post-thyroidectomy), low intake/Vitamin D, CKD, bisphosphonates, aminoglycosides.
  • Signs: CRAMPS (convulsions, reflexes ↑, arrhythmias, muscle spasms/tetany, positive Trousseau/Chvostek’s, paresthesia).
  • Hypercalcemia: caused by hyperparathyroidism, excess vitamin D/Ca, bone cancer, thiazides, lithium.
  • Signs: WEAK (weakness, EKG changes, absent reflexes, abdominal distension, kidney stones).

Magnesium (Mg2+)

  • Normal: 1.5–2.5 mg/dL; intracellular, helps nerve/muscle and with Na+/K+ pump.
  • Absorbed in small intestine; low often with low Ca2+ and K+.
  • Hypomagnesemia: caused by low intake, GI disorders, PPIs, alcoholism.
  • Signs: TWITCH (Trousseau/Chvostek, weakness, ↑ reflexes, torsades de pointes, tetany, low Ca2+/K+, hypertension).
  • Hypermagnesemia: from excess Mg2+ supplements or renal failure.
  • Signs: LETHARGIC (lethargy, EKG changes, tendon reflexes absent, hypotension, arrhythmias, red/hot face, GI issues, impaired breathing, confusion).

Phosphate (PO4^3-)

  • Normal: 2.5–4.5 mg/dL; bone/teeth health, regulated by PTH/vitamin D/kidneys.
  • Hypophosphatemia: from antacids, starvation, refeeding, hyperparathyroidism, low vitamin D.
  • Signs: BONE (bone pain/fractures, osteomalacia, neuro changes, erythrocyte destruction).
  • Hyperphosphatemia: from phosphate laxatives, renal failure, excess vitamin D, rhabdomyolysis, hypoparathyroidism.
  • Signs: like hypocalcemia (convulsions, reflexes ↑, arrhythmias, muscle spasms, pruritus).

Key Terms & Definitions

  • Electrolyte — Ion in body fluids important for physiological processes.
  • Hyponatremia — Low sodium level (<135 mEq/L).
  • Hypernatremia — High sodium level (>145 mEq/L).
  • Hypokalemia — Low potassium (<3.5 mEq/L).
  • Hyperkalemia — High potassium (>5 mEq/L).
  • Hypocalcemia — Low calcium (<8.5 mg/dL).
  • Hypercalcemia — High calcium (>10.5 mg/dL).
  • Hypomagnesemia — Low magnesium (<1.5 mg/dL).
  • Hypermagnesemia — High magnesium (>2.5 mg/dL).
  • Hypophosphatemia — Low phosphate (<2.5 mg/dL).
  • Hyperphosphatemia — High phosphate (>4.5 mg/dL).
  • SIADH — Syndrome of inappropriate antidiuretic hormone secretion.
  • Trousseau’s/Chvostek’s signs — Physical signs indicating low calcium or magnesium.

Action Items / Next Steps

  • Review the lecture material and access the free quiz to test your knowledge on fluid and electrolyte imbalances.

Full transcript