Management of Infusotherapy for Hypocalcemia, Hypomagnesemia, and Hypokalemia
For a patient with concurrent hypocalcemia, hypomagnesemia, and hypokalemia, magnesium replacement should be prioritized first, followed by calcium and then potassium, as magnesium deficiency can cause both hypocalcemia and hypokalemia that are refractory to replacement without correcting the underlying magnesium deficit. 1
Order of Electrolyte Replacement
1. Magnesium Replacement (First Priority)
For mild hypomagnesemia:
- IV magnesium sulfate 1 g (8.12 mEq) every 6 hours for 4 doses 2
- Dilute to concentration of 20% or less prior to administration
- Use 5% Dextrose or 0.9% Sodium Chloride as diluent
For severe hypomagnesemia:
- IV magnesium sulfate 5 g (40 mEq) added to 1 liter of IV fluid for slow infusion over 3 hours 2
- Maximum rate should not exceed 150 mg/minute
- Monitor serum magnesium levels to guide therapy
2. Calcium Replacement (Second Priority)
- For hypocalcemia:
- Calcium chloride 20 mg/kg (0.2 mL/kg of 10% CaCl₂) IV 3
- Infuse over 30-60 minutes for non-urgent situations
- Calcium chloride is preferred for critically ill patients as it results in more rapid increase in ionized calcium than calcium gluconate
- Calcium gluconate (60 mg/kg) may be substituted if calcium chloride is not available 3
- Administration through central venous access is preferred to avoid tissue injury from extravasation
3. Potassium Replacement (After magnesium correction)
- For hypokalemia:
- IV potassium chloride at rate not exceeding 10 mEq/hour if serum potassium >2.5 mEq/L 4
- For severe hypokalemia (<2.5 mEq/L), rates up to 40 mEq/hour with continuous cardiac monitoring 4
- Maximum 200 mEq per 24-hour period for moderate hypokalemia
- Maximum 400 mEq per 24-hour period for severe hypokalemia
- Administer via central line for concentrations >60 mEq/L
Monitoring Parameters
- Serum electrolyte levels (Mg, Ca, K) every 4-6 hours until stable
- Continuous cardiac monitoring during rapid replacement
- Monitor for signs of overcorrection:
- Magnesium: loss of deep tendon reflexes, respiratory depression, hypotension
- Calcium: bradycardia, hypotension, cardiac arrhythmias 3
- Potassium: peaked T waves, widened QRS, cardiac arrhythmias
Special Considerations
Interrelationship of Electrolytes
- Hypomagnesemia can cause refractory hypocalcemia by suppressing parathyroid hormone secretion 5
- Hypomagnesemia can cause refractory hypokalemia by increasing renal potassium wasting 1
- Up to 42% of patients with hypokalemia have concurrent hypomagnesemia 6
- Correcting magnesium alone may normalize calcium levels without additional calcium supplementation 5
Common Pitfalls to Avoid
- Do not correct potassium or calcium without addressing magnesium deficiency first, as this approach will likely fail 1, 5
- Do not administer calcium and bicarbonate solutions simultaneously as they may precipitate 3
- Do not administer magnesium too rapidly (>150 mg/minute) as it may cause hypotension 2
- Do not administer high concentration potassium solutions peripherally due to risk of phlebitis and pain 4
- Do not fail to identify and address the underlying cause of electrolyte abnormalities (e.g., medications, malabsorption, renal losses)
Underlying Causes to Consider
- Aminoglycoside therapy (causes magnesium wasting) 7, 8
- Short bowel syndrome 1
- Continuous kidney replacement therapy 3
- Malnutrition or refeeding syndrome 3
- Diuretic therapy 3
By following this systematic approach to electrolyte replacement with careful attention to the sequence of correction and appropriate monitoring, you can effectively manage patients with concurrent hypocalcemia, hypomagnesemia, and hypokalemia while minimizing complications.