Fluid and electrolyte disorders
Also known as: fluid and electrolyte imbalances
Fluid and electrolyte disorders are conditions in which body water volume or the concentration of key electrolytes — sodium, potassium, calcium, magnesium, phosphate — falls outside its normal range. They arise from losses, excess intake, or impaired regulation by the kidneys and endocrine system.
Body water is distributed between intracellular and extracellular compartments, and electrolytes dissolved in that water maintain osmotic balance, nerve conduction, muscle contraction, and acid-base status. Disorders occur when intake, output, and hormonal regulation fall out of alignment — through vomiting, diarrhea, diuretics, burns, renal disease, heart failure, or disorders of antidiuretic hormone and aldosterone.
Volume problems come in two directions. Hypovolemia — from hemorrhage, dehydration, or third spacing — presents with tachycardia, hypotension, poor skin turgor, dry mucous membranes, concentrated urine, and low urine output. Hypervolemia — from fluid overload, heart failure, or renal failure — presents with edema, weight gain, distended neck veins, crackles on auscultation, and bounding pulses. Daily weight is the most sensitive bedside indicator of fluid status, since one kilogram of weight change corresponds to roughly one liter of fluid.
Individual electrolytes produce characteristic patterns. Sodium disorders chiefly affect the brain, with hyponatremia causing confusion, headache, and seizures. Potassium disorders affect the heart: hypokalemia flattens T waves and produces U waves, while hyperkalemia produces peaked T waves and can progress to lethal arrhythmias. Hypocalcemia causes tetany with positive Chvostek and Trousseau signs, whereas hypercalcemia causes lethargy, weakness, and constipation. Magnesium imbalances often accompany potassium and calcium disturbances and can make them refractory to correction.
NCLEX covers fluid and electrolyte disorders under physiological adaptation, and the topic is among the most heavily represented on the exam. Questions typically supply a set of lab values or assessment findings and ask you to identify the imbalance, prioritize which patient to see first, or select the correct nursing intervention — so learn the normal ranges and the signature signs for each electrolyte.
Key takeaways
- Fluid and electrolyte disorders result from imbalances in water volume or in sodium, potassium, calcium, magnesium, and phosphate levels.
- Hypovolemia produces tachycardia, hypotension, and poor turgor; hypervolemia produces edema, weight gain, and crackles.
- Daily weight is the most sensitive indicator of fluid status — about 1 kg of change per liter of fluid.
- Potassium disorders are dangerous because of their cardiac effects, while sodium disorders chiefly cause neurologic symptoms.