• Clinical science
  • Physician

Electrolyte repletion

Summary

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).

Potassium repletion

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

Acute management checklist

Repletion regimens for hypokalemia [1][2]

Serum potassium level Recommended regimen Monitoring

< 2.5 mEq/L

and/or symptomatic

  • Monitor serum potassium every hour.
  • Serial ECG and continuous telemetry recommended
  • Consider ICU level of care

2.5 mEq/L–2.9 mEq/L

and/or unable to tolerate PO

  • Intravenous potassium chloride via peripheral line
  • Maximum rate of 10 mEq/L per hour recommended for peripheral IV
  • Monitor serum potassium at least daily.
  • Consider continuous telemetry

3.0–3.4 mEq/L

  • Monitor serum potassium daily.
≥ 3.5 mEq/L
  • Repletion generally not necessary.
  • Consider oral potassium chloride for patients with DKA, CHF, and/or undergoing active diuresis
  • Monitor serum potassium as needed.

The maximum rate of potassium chloride should not exceed 10 mEq/L in a peripheral IV and 40 mEq/L in a central line.

General considerations

  • Goal serum potassium level: ∼ 4.0 mEq/L
  • Expected increase in serum potassium levels: ∼ 0.1 mEq/L after an IV dose of 10 mEq
  • Use caution with repletion in patients with impaired renal function.

Adverse effects of potassium repletion

Calcium repletion

Acute management checklist

Repletion regimens for hypocalcemia [3][4]

Corrected serum calcium

Recommended regimen Monitoring

≤ 7.5 mg/dL

(ionized Ca ≤ 3.0 mg/dL)

and/or symptomatic

  • IV calcium
    • IV calcium gluconate
    • IV calcium chloride
  • Monitor serum calcium level every 4–8 hours.
  • Continuous telemetry and frequent vital sign monitoring
  • Consider ICU level of care.

7.6 mg/dL–8.4 mg/dL

(ionized Ca 3.1–4.3 mg/dL)

  • Oral calcium
    • Calcium carbonate
    • Calcium citrate
  • Monitor serum calcium level daily or as needed.

≥ 8.5 mg/dL

(ionized Ca ≥ 4.4 mg/dL)

  • No repletion indicated
  • Monitor serum calcium as needed.

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.

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

Magnesium repletion

Acute management checklist

Repletion regimens for hypomagnesemia [5][6][7]

Serum magnesium

Recommended regimen Monitoring

< 1 mEq/dL

and/or symptomatic

  • Monitor serum magnesium 6–12 hours after every dose of IV magnesium.
  • Continuous telemetry
1.0–1.5 mEq/dL
  • Monitor serum magnesium 6–12 hours after every dose of IV magnesium or at least daily.

≥ 1.6 mEq/dL


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

Differential diagnoses of hypomagnesemia

Causes [7][5]
Gastrointestinal
Renal
Endocrine
Cell shifts
Medications/Drugs
Other

Phosphate repletion

Acute management checklist

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). [8]

For patients who are critically ill and/or receiving parenteral nutrition [9][10]

Serum phosphorus Recommended regimen Monitoring

< 1.6 mg/dL

(< 0.51 mmol/L)

  • Monitor serum phosphorus level 6 hours after infusion.
  • Consider continuous telemetry

1.6–2.2 mg/dL

(0.51–0.71 mmol/L)

  • Monitor serum phosphorus level 6 hours after infusion.

2.2–3.0 mg/dL

(0.71–0.96 mmol/L)

  • Monitor serum phosphorus level 6 hours after infusion.

All other patients [6][10]

Serum phosphorus Recommended regimen Monitoring

< 1.0 mg/dL (< 0.32 mmol/L),

symptomatic, and/or unable to take PO

  • Monitor serum phosphorus level 6 hours after infusion.

1.0–1.9 mg/dL

(0.32–0.64 mmol/L)

  • Monitor serum phosphorus level 6 hours after infusion (if IV) or at least daily.

≥ 2.0 mg/dL

(> 0.64 mmol/L)

  • Repletion generally not indicated
  • Monitor serum phosphorus as needed

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 [8]
    • 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 [10]

Differential diagnoses of hypophosphatemia

Causes [10]
Gastrointestinal
Critical illness
Medications/iatrogenic
Other
  • 1. Cohn JN, Kowey PR, Whelton PK, Prisant LM. New Guidelines for Potassium Replacement in Clinical Practice. Arch Intern Med. 2000; 160(16): p. 2429. doi: 10.1001/archinte.160.16.2429.
  • 2. Kardalas E, Paschou SA, Anagnostis P, Muscogiuri G, Siasos G, Vryonidou A. Hypokalemia: a clinical update. Endocrine Connections. 2018; 7(4): pp. R135–R146. doi: 10.1530/ec-18-0109.
  • 3. Schafer AL, Shoback DM. Hypocalcemia: Diagnosis and Treatment. https://www.ncbi.nlm.nih.gov/books/NBK279022/. Updated January 3, 2016. Accessed July 4, 2019.
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  • 6. Kraft MD, Btaiche IF, Sacks GS, Kudsk KA. Treatment of electrolyte disorders in adult patients in the intensive care unit. American Journal of Health-System Pharmacy. 2005; 62(16): pp. 1663–1682. doi: 10.2146/ajhp040300.
  • 7. Hansen B-A, Bruserud Ø. Hypomagnesemia in critically ill patients. Journal of Intensive Care. 2018; 6(1). doi: 10.1186/s40560-018-0291-y.
  • 8. Iheagwara OS, Ing TS, Kjellstrand CM, Lew SQ. Phosphorus, phosphorous, and phosphate. Hemodialysis International. 2012: pp. n/a–n/a. doi: 10.1111/hdi.12010.
  • 9. Brown KA, Dickerson RN, Morgan LM, Alexander KH, Minard G, Brown RO. A New Graduated Dosing Regimen for Phosphorus Replacement in Patients Receiving Nutrition Support. Journal of Parenteral and Enteral Nutrition. 2006; 30(3): pp. 209–214. doi: 10.1177/0148607106030003209.
  • 10. Miller DW, Slovis CM. Hypophosphatemia in the emergency department therapeutics. Am J Emerg Med. 2000; 18(4): pp. 457–461. doi: 10.1053/ajem.2000.7347.
last updated 11/27/2019
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