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Calculation of the Potassium Deficit


Potassium Deficit calculator

Background

Hypokalemia is one of the most common water-electrolyte imbalances and affects about 20% of patients admitted to the hospital medical surgical services and about 40% of patients admitted to intensive care units.
The most common causes of hypokalemia defined as a level below 3.5 mEq/L (3.5 mmol/L) include vomiting, diarrhea, hypomagnesemia, diuretics such as furosemide, hyperaldosteronism, and less commonly inadequate intake.  Normal potassium levels are between 3.5 and 5.0 mEq/L.  Mildly low potassium levels (3.0 to 3.5 mEq/L) typically do not cause symptoms, however, may lead to increases in blood pressure and provoke the development of an abnormal heart rhythm. Moderate hypokalemia (serum potassium levels of 2.5 to 3 mEq/L (2.5 - 3.0 mmol/L), may cause muscle weakness, tiredness, myalgia, tremor, muscle cramps, and constipation.  Severe deficits leading to serum potassium levels below 2.5 mEq/L may be life-threatening and lead to electrocardiographic (ECG) changes such as QRS prolongation, ST-segment and T-wave depression, and U-wave formation. The earliest (ECG) findings in patients with hypokalemia are decreased T wave height, followed by ST depressions and T inversions as levels continue to fall. 

 

Calculating deficits

The program will estimate the potassium deficit through the use of empirically derived ranges that are based on current levels.  In addition, the following equation will be used: 

Potassium Deficit Equation

Kdeficit (in mmol)=(Knormal lower limit -Kmeasured) x body weight (kg) x 0.4

The size of the deficit is difficult to determine because only 2% of the body's potassium is present in the extracellular fluid.

Many factors in addition to the total body potassium stores contribute to the serum K+ concentration so it is possible to either underestimate or overestimate the actual deficit.  This equation also does not take into account the daily losses/requirements of potassium that are needed in addition to the deficit.




Required Entries





Weight

Current Potassium Level  
       [Value below 3.5 mEq/L (mmol/L]


Describe current symptoms of hypokalemia:



heart


 
 


Key Statements


Reference

Alldredge B.K., Corelli R.L., Ernst M.E., Guglielmo B.J., Jacobson P.A., Kradjan W.A. Koda-Kimble and Young’s Applied Therapeutics: The Clinical Use of Drugs. 10th ed. Lippincott; Philadelphia, PA, USA: 2013.


  • The kidneys are responsible for about 90% of daily potassium loss (~40 - 90 mEq/day).
  • The kidneys have only a limited ability to conserve potassium - with little to no intake of potassium, the urine will still contain at least 5 to 20 mEq of potassium per 24 hours.
  • Hypomagnesemia often accompanies hypokalemia - hypokalemic individuals not responding to potassium therapy may be refractory to treatment until hypomagnesemia is corrected.
  • When evaluating hypokalemia, the clinician should determine whether the hypokalemia is a result of lowintake, increased cellular uptake of potassium, or excessive loss of potassium via the kidneys, GI tract, or skin.
  • Inadequate intake rarely is the sole cause of potassium depletion unless inappropriate and continued renal or extrarenal losses occur, or potassium intake is severely restricted to less than 10 to 15 mEq/day.
  •  The urinary potassium concentration is a good marker for differentiating various hypokalemic syndromes. A urinary potassium excretion of less than 20 mEq/day suggests extrarenal potassium loss.
  • The amount of potassium deficit and the rate of continued potassium loss should be determined to guide replacement therapy. It has been estimated that a 1-mEq/L fall in serum potassium from 4 to 3 mEq/L represents a total body deficit of approximately 200 mEq.
  • See  calculator results page....


 


References top of page

 

  1. Aboujamous et al. Evaluation of the Change in Serum Potassium Levels after Potassium Administration. J Clin Nephrol Ren Care 2016, 2:013,
  2. Asmar A, Mohandas R, Wingo CS. A Physiologic-Based Approach to the Treatment of a Patient With Hypokalemia. Am J Kidney Dis. 2012 September ; 60(3): 492-497.
  3. Cohn JN, Kowey PR, et al. New guidelines for potassium replacement in clinical practice: A contemporary review by the National Council on Potassium in Clinical Practice. Arch Intern MED/VOL 160, SEP 11, 2000.
  4. Gennari FJ. Disorders of potassium homeostasis: Hypokalemia and hyperkalemia. Crit Care Clin. 2002;18(2):273-288.
  5. Gennari FJ. Hypokalemia. N Engl J Med. 1998;339(7):451-458.
  6. Kamel KS, Quaggin S, Scheich A, et al. Disorders of potassium homeostasis: an approach based on pathophysiology. Am J Kidney Dis 1994;24:597-613.
  7. Kardalas E, et al. Hypokalemia: a clinical update. Endocrine Connections (2018) 7, R135-R146.
  8. Kim GH, Han JS. Therapeutic approach to hypokalemia. Nephron. 2002;92(suppl 1):28-32.
  9. Lippi G, Favaloro EJ, Montagnana M, Guidi GC. Prevalence of hypokalaemia:the experience of a large academic hospital. Intern Med J. 2010;40(4):315-316.
  10. Rastergar A, Soleimani M. Hypokalaemia and hyperkalaemia. Postgrad Med J 2001;77:759-764.
  11. Viera AJ, Wouk N. Potassium Disorders: Hypokalemia and Hyperkalemia.Am Fam Physician. 2015;92(6):487-495.
  12. Weiner ID, Wingo CS. Hypokalemia-consequences, causes, and correction. J Am Soc Nephrol. 1997;8(7):1179-1188.
Potassium Deficit Calculator