What is the approach for correcting electrolyte imbalances, including formulas for calculating deficits?

Electrolyte Correction: Clinical Approach and Formulas

Initial Assessment and Monitoring

Begin immediate laboratory evaluation with plasma glucose, BUN, creatinine, serum electrolytes with calculated anion gap, osmolality, urinalysis, arterial blood gases, and complete blood count in all patients with suspected electrolyte imbalance. 1

• Obtain baseline ECG to identify QT prolongation (hypokalemia) or peaked T-waves (hyperkalemia) 1
• Calculate corrected sodium by adding 1.6 mEq/L for each 100 mg/dL glucose above 100 mg/dL 2, 1
• Measure urine electrolytes and osmolality to assess renal handling 1
• Draw blood every 2-4 hours for electrolytes, glucose, BUN, creatinine, and osmolality during active correction 1, 3

Sodium Correction

Hyponatremia

• Limit osmolality changes to <3 mOsm/kg/h to prevent cerebral edema, especially in children 1, 3
• Use isotonic saline (0.9% NaCl) at 15-20 mL/kg/h for the first hour in severe dehydration 2, 4
• After initial resuscitation, switch to 0.45% NaCl at 4-14 mL/kg/h if corrected sodium is normal or elevated 2, 4
• Use 0.9% NaCl at similar rates if corrected sodium is low 2

Hypernatremia

• Replace water deficits gradually over 24-48 hours 2
• Typical total body water deficit in hyperglycemic crises: 6 liters in DKA, 9 liters in HHS 2, 4
• Formula: Water deficit (L) = 0.6 × body weight (kg) × [(current Na/140) - 1] 2

Potassium Correction

Always exclude hypokalemia before starting insulin therapy to prevent life-threatening arrhythmias. 3

Hypokalemia Management

• Delay insulin in DKA if potassium <3.3 mEq/L until repleted 3
• Replace with 20-40 mEq/L potassium chloride in IV infusion 1, 5
• Add 20-30 mEq/L potassium (2/3 KCl and 1/3 KPO4) to maintenance fluids once renal function confirmed 2, 4
• Recheck potassium within 1-2 hours after IV correction, then every 2-4 hours until stabilized 3
• Typical total body potassium deficit in DKA: 3-5 mEq/kg; in HHS: 5-15 mEq/kg 2

Critical Pitfall

• Correct hypomagnesemia before treating hypokalemia, as magnesium deficiency impairs potassium repletion 3
• Use potassium chloride rather than potassium citrate to avoid worsening metabolic alkalosis 3

Magnesium Correction

Hypomagnesemia

• For mild deficiency: 1 g (8.12 mEq) IM every 6 hours for 4 doses 6
• For severe hypomagnesemia: up to 250 mg/kg (approximately 2 mEq/kg) IM within 4 hours 6
• Alternative: 5 g (40 mEq) in 1 liter D5W or NS over 3 hours IV 6
• Use organic magnesium salts for better bioavailability 1
• Target magnesium level >0.6 mmol/L (>1.4 mg/dL) 3
• Typical total body magnesium deficit in hyperglycemic crises: 5-7 mEq/kg in DKA, 4-6 mEq/kg in HHS 2

Special Populations

• In eclampsia/pre-eclampsia: Initial dose 4-5 g IV over 3-4 minutes, then 4-5 g IM every 4 hours or 1-2 g/hour continuous infusion 6
• Target serum level of 6 mg/100 mL for seizure control 6
• Maximum dose: 30-40 g per 24 hours (20 g/48 hours in severe renal insufficiency) 6

Phosphate Correction

• Typical total body phosphate deficit in hyperglycemic crises: 3-5 mmol/kg 2
• Use phosphate-containing KRT solutions to prevent CKRT-related hypophosphatemia 2
• Include 1/3 of potassium replacement as KPO4 2, 4

Chloride Management

• Typical total body chloride deficit in DKA: 3-5 mEq/kg; in HHS: 5-13 mEq/kg 2
• Use balanced crystalloids preferentially over 0.9% saline to avoid hyperchloremic acidosis 2
• Limit 0.9% saline use in patients with existing acidosis or hyperchloremia 2

Pediatric Considerations

• Provide sodium 2-4 mmol/kg/d, potassium 1-3 mmol/kg/d, chloride 2-4 mmol/kg/d in parenteral nutrition 2, 1
• Monitor serum electrolytes and weight daily 1
• Initial fluid resuscitation: 10-20 mL/kg/h for first hour, not exceeding 50 mL/kg over first 4 hours 4

Context-Specific Adjustments

Kidney Replacement Therapy

• Use dialysis solutions containing potassium (4 mEq/L), phosphate, and magnesium to prevent electrolyte disorders 2, 1
• Monitor electrolytes every 2-4 hours initially 1

Critical Illness/Sepsis

• Correct electrolyte imbalances before initiating QT-prolonging agents 3
• Monitor periodically throughout treatment 3

Malnutrition

• Correct electrolyte imbalances using IV or oral supplements before starting enteral feeding 3

Common Pitfalls to Avoid

• Never exceed 150 mg/minute IV magnesium infusion rate (except severe eclampsia with seizures) 6
• Avoid continuous magnesium sulfate in pregnancy beyond 5-7 days (causes fetal abnormalities) 6
• Do not use hydroxyethyl starch solutions (increased mortality and kidney failure) 2
• Always identify and treat underlying causes (infection, medications, endocrinopathies) to prevent recurrence 1
• Monitor fluid input/output and hemodynamic parameters continuously during correction 2, 1