Definition of Electrolyte Imbalance
An electrolyte imbalance is an abnormal concentration of essential electrolytes (sodium, potassium, chloride, calcium, magnesium, or phosphate) in the blood, either elevated or decreased from normal physiological ranges, which disrupts cellular function and can lead to life-threatening complications. 1, 2
Core Electrolytes and Their Normal Ranges
The key electrolytes that maintain cellular neutrality and enable action potential generation include 1, 3:
- Sodium: 135-145 mEq/L 1
- Potassium: 3.5-5.3 mEq/L 1
- Chloride: 95-105 mEq/L 1
- Calcium: 4.4-5.2 mEq/L 1
- Magnesium: 1.6-2.4 mEq/L 1
- Phosphate: >0.81 mmol/L (hypophosphatemia defined as <0.81 mmol/L) 1
Clinical Significance and Pathophysiology
Electrolyte imbalances interfere with normal physiological activities and may result in life-threatening consequences. 3 These abnormalities are common in hospitalized patients, affecting approximately 15-30% of children and adults, with cumulative incidence up to 65% in critically ill patients. 1
Mechanisms of Imbalance
Electrolyte disorders develop through three primary mechanisms 1:
- Inadequate intake or decreased intestinal absorption
- Redistribution between intracellular and extracellular compartments
- Excessive losses (renal, gastrointestinal, or through medical interventions)
Common Clinical Presentations
Hyponatremia (Sodium <135 mEq/L)
The most common electrolyte abnormality in hospitalized patients, hyponatremia results from impaired free-water excretion, often due to excess arginine vasopressin (AVP) release triggered by pain, nausea, stress, postoperative states, or conditions like pneumonia and meningitis. 1 Symptoms include fussiness, headache, nausea, vomiting, confusion, lethargy, and muscle cramps, with the most serious complication being hyponatremic encephalopathy—a medical emergency that can be fatal or cause irreversible brain injury. 1
Hyperkalemia (Potassium >5.0-5.5 mEq/L)
Hyperkalemia is an electrolyte abnormality with potentially life-threatening consequences, particularly in patients with chronic kidney disease, diabetes, heart failure, or those receiving renin-angiotensin-aldosterone system inhibitor therapy. 1 It increases the risk of cardiac arrhythmias and sudden death. 4, 5
Hypophosphatemia, Hypokalemia, and Hypomagnesemia
These deficiencies commonly occur during intensive kidney replacement therapy, with hypophosphatemia affecting 60-80% of ICU patients and hypomagnesemia affecting up to 60-65% of critically ill patients. 1, 6 Hypophosphatemia is associated with worsening respiratory failure, prolonged mechanical ventilation weaning, cardiac arrhythmias, and prolonged hospitalization. 1
High-Risk Clinical Scenarios
Refeeding Syndrome
When artificial nutritional support is initiated in recently starved patients, the body's adaptation to undernutrition (down-regulated membrane pumping with intracellular electrolyte leakage) suddenly reverses. 1 This causes precipitous falls in circulating potassium, magnesium, calcium, and phosphate levels, along with acute increases in extracellular fluid, creating considerable danger of cardiac and respiratory failure, lethargy, confusion, coma, and death. 1
Cardiopulmonary Bypass
Tissue hypoxia or electrolyte imbalance during cardiopulmonary bypass increases the risk of tissue injury and organ dysfunction. 1 Excessive use of normal saline or unbalanced colloid solutions leads to hyperchloremic acidosis due to supra-physiological chloride concentrations (>154 mmol/L). 1
Critical Monitoring Considerations
Electrolyte abnormalities must be closely monitored in all high-risk patients, particularly those with kidney disease receiving kidney replacement therapy. 1, 7 Monitoring frequency should be increased for patients with chronic kidney disease, diabetes, heart failure, history of hyperkalemia, or those receiving medications affecting electrolyte balance. 1, 4
Common Pitfall
Measurements of magnesium and potassium in serum or plasma are of limited value to assess true electrolyte status, as these are mainly intracellular ions with no correlation between intracellular content and plasma levels. 5 Despite this limitation, plasma measurements remain the standard for clinical decision-making and must be interpreted in the context of the patient's clinical condition and risk factors.