Electrolyte repletion

Hypokalemia, hypocalcemia, hypomagnesemia, and hypophosphatemia are common electrolyte disturbances in hospitalized and critically ill patients. Repletion regimens vary widely and standardized recommendations do not exist. For this reason, institutional guidelines and individual patient factors should always be taken into consideration when planning electrolyte repletion. Always consider renal and hepatic clearance and the potential for adverse effects when repleting electrolytes and attempt to identify and treat the underlying cause. It is also important to correct any concurrent electrolyte abnormalities (e.g., repletion of concurrent hypomagnesemia in a patient with hypokalemia) and consider the level of monitoring required during the correction (e.g., continuous telemetry during high-dose IV potassium repletion).

Always check the serum magnesium level and replete magnesium prior to repleting potassium. Low magnesium can exacerbate renal potassium losses.

Repletion regimens

Various concentrations of potassium chloride are available; consult your local hospital protocol. IV solutions with high concentrations (e.g., 300–400 mEq/L) should be exclusively administered via a central line.

The maximum infusion rate of potassium chloride should not exceed 10–20 mEq/L per hour in a peripheral IV or 40 mEq/L per hour in a central line.

General considerations

• Therapeutic goals
  • Target serum potassium level: ∼ 4.0 mEq/L
  • Expected increase in serum potassium levels: ∼ 0.1 mEq/L after an IV dose of 10 mEq
• Route of replacement: depends on hypokalemia severity, symptoms, and ability to tolerate/absorb oral medication
  • Oral supplementation is typically preferred, due to a lower risk of cardiac arrhythmia and venous sclerosis.
  • IV and oral supplementation can be combined in severe cases where GI absorption is intact.
  • Oral uptake can be improved by administration with or after a meal. ^[2]
• Cautions
  • Replete potassium judiciously in patients with impaired renal function to avoid rebound hyperkalemia.
  • Avoid transcellular potassium shift by using regular saline instead of 5% glucose as infusion fluid. ^[2]
  • In patients with a high risk of sudden cardiac arrest (e.g., post-MI, preexisting QT prolongation): ; ^[6][7][8]
    • Maintain normal potassium and magnesium levels.
    • Treat torsades de pointes with IV magnesium.

Adverse effects of potassium repletion

• Hyperkalemia
• Cardiac arrhythmias ^[9]
• GI upset (PO administration)
• Extravasation (IV administration)
• Local irritation (IV administration)

Acute management checklist for hypokalemia

• Check ECG.
• Replete potassium according to severity (see repletion regimens for hypokalemia).
• Identify and treat the underlying cause (see differential diagnoses of hypokalemia).
• Identify and treat hypomagnesemia (see repletion regimens for hypomagnesemia).
• Discontinue any contributing medications.
• Consider starting a potassium-sparing diuretic (if appropriate).
• Restrict dietary sodium intake.
• Encourage dietary potassium intake.
• Order monitoring labs.
• Continuous telemetry and serial ECGs if hypokalemia is severe (< 3.0 mEq/L) or symptomatic

Repletion regimens

Use extreme caution when administering IV calcium in patients receiving cardiac glycosides or avoid it altogether, as the combination increases the risk of ventricular fibrillation.

If hypomagnesemia is present, replete magnesium concurrently with calcium as low magnesium can disrupt PTH-mediated calcium hemostasis. ^[12]

General considerations

• Goal serum calcium level: low–normal range (e.g., ∼ 8.5 mg/dL)
• The ionized calcium level is the best measure of physiologically active calcium.
• When using serum calcium, make sure to correct for albumin.

Adverse effects of calcium repletion

• Local irritation
• IV extravasation and soft tissue calcifications
• Hypotension, bradycardia, cardiac arrest

Acute management checklist for hypocalcemia

• Confirm hypocalcemia (i.e., check ionized calcium and/or correct serum calcium for albumin).
• Replete calcium according to severity (see repletion regimens for hypocalcemia).
• Identify and treat hypomagnesemia (see repletion regimens for hypomagnesemia).
• Identify and treat hypokalemia (see repletion regimens for hypokalemia).
• Identify and treat vitamin D deficiency.
• Identify and treat the underlying cause (see causes of hypocalcemia).
• Discontinue any contributing medications (e.g., loop diuretics).
• Order monitoring labs.
• Continuous telemetry in patients with severe (< 7.5 mg/dL) or symptomatic hypocalcemia

Repletion regimens

Because the risk of hypermagnesemia is elevated in patients with impaired renal function (especially if the creatinine clearance is < 30 mL/min/1.73 m²), consider reducing the dose in this group by 50%.

General considerations

• Goal serum magnesium level
  • Most patients: 1.5–2.4 mg/dL
  • In patients with an underlying cardiac disorder and/or at risk of arrhythmias: consider higher goal > 1.7 mg/dL
• 1 g of IV magnesium sulfate has about 8 mEq of elemental magnesium.
• Oral repletion is generally preferred when possible
• Magnesium repletion should be continued 1–2 days after normalization of serum levels.

Adverse effects

• Soft stools, diarrhea
• Nausea, vomiting
• Fatigue
• Muscle weakness, attenuation of muscle reflexes
• Low blood pressure
• Impaired respiratory effort, cardiac arrest
• Hypermagnesemia

Acute management checklist for hypomagnesemia

• Replete magnesium according to severity (see repletion regimens for hypomagnesemia).
• Identify and treat the underlying cause (see differential diagnoses of hypomagnesemia).
• Identify and treat hypocalcemia (see repletion regimens for hypocalcemia).
• Identify and treat hypokalemia (see repletion regimens for hypokalemia).
• Identify and treat hypophosphatemia (see repletion regimens for hypophosphatemia).
• Encourage dietary magnesium intake.
• Order monitoring labs.
• Continuous telemetry if severe < 1 mEq/dL or symptomatic

Repletion regimens for hypophosphatemia

Approach

1. Determine whether IV or PO repletion is indicated.
2. Calculate how many millimoles of elemental phosphorus are indicated.
3. Decide which phosphate salt should be administered.
   • If the serum potassium is < 4.0 mg/dL, administer as potassium phosphate.
   • If the serum potassium is ≥ 4.0 mg/dL, administer as sodium phosphate.
4. Round the total dose calculated to the closest preparation dose available (e.g., typically 7.5 mmol for IV, 8 mmol for PO).

There are no standard guidelines for phosphate repletion and individual recommendations vary. Consult your pharmacy with any questions, as individual formulations may vary!

Do not confuse phosphorous (P) with phosphate (PO₄³⁻). The concentration of the substances measured in mmol/L is identical but the mass measured in mg/dL differs by a ratio of around 3:1 (phosphate:phosphorus). ^[16]

For patients who are critically ill and/or receiving parenteral nutrition ^[17][18]

All other patients ^[14][18]

If the serum potassium is < 4.0 mg/dL, administer phosphate as potassium phosphate. If the serum potassium is ≥ 4.0 mg/dL, administer phosphate as sodium phosphate.

General considerations

• Goal serum phosphorus level: > 2–3 mg/dL
• Expected increase in serum phosphorus levels: ∼ 0.5 mg/dL with a dose of 0.10 mmol/kg body weight (but this is somewhat unpredictable)
• Serum phosphorus levels may not reflect total body stores, as most of the body's phosphorus is stored in the bones and soft tissues.
• Critically ill patients often have higher phosphorus requirements due to hypermetabolism and high urinary phosphorus excretion.
• Dosing
  • A standard IV dose is around 15–30 mmol and should not be administered faster than 4.5–7.0 mmol/hour.
  • Reduce the dose by 50% in patients with impaired renal function who are not on hemodialysis.
• Phosphorus preparations ^[16]
  • 1 mmol of potassium phosphate contains ∼ 1.5 mEq of potassium.
  • 1 mmol of sodium phosphate contains ∼ 1.33 mEq of sodium.

For IV administration, round the total phosphate dose to the nearest 7.5 mmol for ease of preparation

Adverse effects of phosphate repletion ^[18]

• Hypocalcemia, hypernatremia
• Osmotic diuresis
• Renal failure
• Arrhythmias
• Confusion, dizziness, seizure, tetany
• Precipitation with calcium
• Hyperkalemia
• Diarrhea, flatulence, nausea, vomiting
• Sore throat

Acute management checklist for hypophosphatemia

• Determine if the patient is critically ill or is receiving parenteral nutrition.
• Replete phosphate according to serum phosphorus levels and serum potassium levels (see repletion regimens for hypophosphatemia).
• Identify and treat the underlying cause (see differential diagnoses of hypophosphatemia).
• Order monitoring labs.