Calculation of the Potassium Deficit
Potassium related content
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:
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
-
Aboujamous et al. Evaluation of the Change in Serum Potassium Levels after
Potassium Administration. J Clin Nephrol Ren Care 2016, 2:013,
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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.
-
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.
-
Gennari FJ. Disorders of potassium homeostasis: Hypokalemia and
hyperkalemia. Crit Care Clin. 2002;18(2):273-288.
-
Gennari FJ. Hypokalemia. N Engl J Med. 1998;339(7):451-458.
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Kamel KS, Quaggin S, Scheich A, et al. Disorders of potassium homeostasis:
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-
Kardalas E, et al. Hypokalemia: a clinical update. Endocrine Connections
(2018) 7, R135-R146.
-
Kim GH, Han JS. Therapeutic approach to hypokalemia. Nephron. 2002;92(suppl
1):28-32.
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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.
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Rastergar A, Soleimani M. Hypokalaemia and hyperkalaemia. Postgrad Med J
2001;77:759-764.
- Viera AJ, Wouk N. Potassium Disorders:
Hypokalemia and Hyperkalemia.Am Fam Physician. 2015;92(6):487-495.
- Weiner ID, Wingo CS.
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