What do abnormal electrolyte results mean?

Understanding Abnormal Electrolyte Results

Abnormal electrolyte results indicate potentially life-threatening disturbances in sodium, potassium, magnesium, calcium, and phosphate that require immediate recognition and treatment to prevent cardiac arrhythmias, neurological complications, and death. 1

Most Common Electrolyte Abnormalities

Hyponatremia (Low Sodium)

• Hyponatremia is the most frequent electrolyte disorder in hospitalized patients, affecting 15-30% of children and adults 1, 2
• Symptoms are often nonspecific: confusion, nausea, headache, lethargy, muscle cramps, and in severe cases, seizures and coma 1, 3
• Hospital-acquired hyponatremia typically results from administering hypotonic IV fluids in patients with elevated antidiuretic hormone (ADH) from pain, stress, surgery, pneumonia, or meningitis 1
• The most serious complication is hyponatremic encephalopathy, which can cause permanent brain injury or death if inadequately treated 1

Hyperkalemia (High Potassium)

• Hyperkalemia is one of the few electrolyte disturbances that can directly cause cardiac arrest 4, 5
• ECG changes progress predictably: peaked T waves (5.5-6.5 mmol/L), flattened P waves and prolonged PR interval (6.5-7.5 mmol/L), widened QRS complex (7.0-8.0 mmol/L), and sine wave pattern leading to ventricular fibrillation or asystole (>10 mmol/L) 1, 4, 5
• However, ECG manifestations vary significantly among individuals and may not be predictable, requiring careful clinical correlation 1, 5
• Most commonly occurs with renal failure or massive potassium release from cells 5

Hypokalemia (Low Potassium)

• The most common electrolyte abnormality encountered in clinical practice 5, 6
• ECG findings include broadening of T waves, ST-segment depression, prominent U waves (>1 mm), and QT interval prolongation 4, 5
• Increases risk of ventricular arrhythmias including premature ventricular contractions, ventricular tachycardia, torsades de pointes, and ventricular fibrillation 5
• Heart failure patients should maintain potassium levels ≥4 mEq/L to prevent arrhythmias 4, 5

Hypophosphatemia (Low Phosphate)

• Prevalence reaches 60-80% among ICU patients, especially those on kidney replacement therapy 1
• Associated with worsening respiratory failure, prolonged weaning from mechanical ventilation, cardiac arrhythmias, and prolonged hospitalization 1
• Can develop as part of refeeding syndrome when nutrition is restarted after starvation, particularly when carbohydrate calories are emphasized 1

Hypomagnesemia (Low Magnesium)

• Contributes to QT prolongation and increases risk of torsades de pointes, even when magnesium levels appear normal 1, 5
• Magnesium bolus or infusion is recommended for torsades de pointes regardless of baseline magnesium level 1, 4, 5
• Often coexists with hypokalemia and must be corrected concurrently for effective potassium repletion 5

Critical Monitoring Requirements

Electrolyte abnormalities are common in hospitalized patients with cumulative incidence up to 65%, especially in critically ill patients, and shall be closely monitored 1

When Continuous ECG Monitoring is Mandatory:

• Moderate to severe potassium or magnesium imbalances 1, 5
• Any electrolyte abnormality with ECG changes 1, 5
• Patients with cardiac comorbidities and electrolyte disturbances 5
• During treatment of severe electrolyte abnormalities 5

Refeeding Syndrome: A Critical Pitfall

When restarting nutrition after starvation, refeeding syndrome can cause precipitous falls in potassium, magnesium, calcium, and phosphate, leading to cardiac and respiratory failure, confusion, coma, and death 1

Mechanism:

• Starvation causes intracellular electrolyte depletion with leakage into blood 1
• Sudden feeding reverses this process, with insulin driving electrolytes back into cells 1
• Results in dangerous drops in circulating electrolyte levels 1

Prevention Strategy:

• Start feeding at approximately 10 kcal/kg/day in very high-risk patients 1
• Provide generous potassium, magnesium, calcium, and phosphate supplements from the start 1
• Give thiamine and B vitamins intravenously before feeding begins and continue for at least 3 days 1
• Close monitoring of electrolytes is essential 1

Common Clinical Pitfalls to Avoid

• Do not assume a normal ECG excludes significant electrolyte abnormality, as ECG changes in hyperkalemia are unpredictable and variable 1, 5
• Always check magnesium when treating hypokalemia, as concurrent hypomagnesemia prevents effective potassium repletion 5
• Do not assume correcting plasma electrolytes before feeding provides safety—severely malnourished patients have massive intracellular deficits requiring simultaneous feeding and supplementation 1
• Electrolyte abnormalities should not be assumed as the sole cause of arrhythmias; patients require full evaluation even when electrolyte disturbances are present 1

Treatment Principles

For Severe Hyperkalemia with ECG Changes:

• Stabilize myocardial membrane with calcium chloride or calcium gluconate 4
• Shift potassium into cells with sodium bicarbonate, glucose plus insulin, or nebulized albuterol 4
• Promote potassium excretion with diuresis, potassium binders, or dialysis 4

For Hypovolemic Hyponatremia:

• Rehydration with isotonic saline (0.9% NaCl) 3, 2

For Severe Symptomatic Hyponatremia:

• Hypertonic saline with careful monitoring to avoid overly rapid correction 3
• Sodium increase must not exceed 10 mmol/L within first 24 hours and 18 mmol/L within first 48 hours to prevent pontine myelinolysis 2

For Euvolemic Hyponatremia (SIADH):

• Restrict free water intake 3, 2
• Address underlying cause 3
• Consider vasopressin receptor antagonists 3