Hypokalemia Potassium Dosing Calculator [Explained]

Hypokalemia (low potassium) Therapy Calculator

Background

Hypokalemia (defined as a serum potassium level of less than 3.5 mmol/L) is one of the most common electrolyte abnormalities encountered in clinical practice with more than 20% of hospitalized patients affected and approximately 40% of ICU patients.   Hypokalemia reflects either total body potassium depletion or redistribution from extracellular fluid to intracellular fluid without potassium depletion.

The most common causes include:   

1. Nonrenal losses (urine K+ < 20 mmol/L): 
   Examples include: diarrhea, vomiting, nasogastric drainage, laxative abuse.
2. Renal losses (urine K+ ≥ 20 mmol/L): 
   Loop diuretics (furosemide, bumetanide, torsemide).
   Thiazide diuretics. 
   Osmotic diuresis e.g. uncontrolled diabetes.
3. Mineralocorticoid excess
4. Primary and secondary hyperaldosteronism
5. Magnesium depletion
6. Transcellular Shifts:
   Insulin administration, 
   β-Adrenergic agonists,
   Acute catecholamine surges,
   Other.

Note: Increased potassium loss (through the kidneys or gastrointestinal tract) is the most common cause of hypokalemia.

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Diagnostic workup:

1. Initially, determine if the patient is symptomatic or arrhythmias are present. Also look for weakness or palpitations, ECG changes, severe hypokalemia (less than 2.5 mEq/L (mmol/L), rapid-onset hypokalemia, or if the patient has underlying heart disease or cirrhosis. This will help determine the acuity of the interventions required.
2. Perform a history and physical examination to look for relevant clinical clues including offending medications, conditions, possible GI losses, and whether or not factitious/spurious hypokalemia is present. Most cases of hypokalemia-induced rhythm disturbances occur in individuals with underlying heart disease.
3. Determine if the lower potassium levels were caused by a transcellular shift (managed by treating the underlying condition or removing the offending agent) or a decrease in total body potassium. A history of paralysis, hyperthyroidism, or use of insulin or beta agonists suggests possible transcellular shifts leading to redistributive hypokalemia.
4. Evaluating the urine potassium, fractional excretion of potassium (FEK) and the Transtubular Potassium Gradient can help differentiate between renal and nonrenal causes of hypokalemia.
5. Urinary potassium levels higher than 20 mmol/L are suggestive of renal causes and levels lower than 20 mmol/L are suggestive of nonrenal causes.
6. Identification and treatment of concurrent hypomagnesemia:  Magnesium depletion reduces the intracellular potassium concentration and causes renal potassium wasting.
7. The diagnosis should be confirmed with a repeat serum potassium measurement. Other laboratory tests include serum glucose and magnesium levels, urine electrolyte and creatinine levels, and acid-base balance.

Required Entries

Data points:

Weight:  Kilograms Pounds

Current Potassium Level:  mEq/L mmol/L  
       [Value below 3.9 mEq/L (mmol/L]


Describe current symptoms of hypokalemia:

None Mild Moderate Severe

[Severe symptoms include:  cardiac arrhythmias, pronounced muscle weakness, paralysis, or ECG changes. ECG changes may include: prominent U wave, flattened or inverted T waves, ST segment depression, T and U wave fusion giving appearance of QT interval prolongation.   Arrhythmias: atrial tachycardia, PVCs, ventricular tachycardia and/or fibrillation, torsades de pointes.]

Select any that apply

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No Yes Patient is able to take oral medications?

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No Yes Magnesium level is in the normal range?

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Hypokalemia predisposes to cardiac arrhythmias by several mechanisms including increased cardiac automaticity, slowed conduction, and delayed ventricular repolarization, predominantly in patients with ischemic heart disease or on digitalis.

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Symptoms  of Hypokalemia 

Symptoms of mild hypokalemia:

• Fatigue
• Weakness
• Respiratory difficulty
• Constipation
• Paralytic ileus
• Leg cramps
• Other

Examples of symptoms by system due to hypokalemia:

Cardiovascular System:

• Worsening hypertension
• ECG changes
• Arrhythmias (especially ventricular arrhythmias), PEA, Aystole.
• Sudden death

Kidney:

• Polyuria due to decreased concentrating ability
• Hypokalemic nephropathy
• Chloride-depletion metabolic alkalosis
• Increased risk of nephrolithiasis

Neuromuscular:

• Cramping
• myalgia
• weakness
• rhabdomyolysis
• paresthesias
• paralysis

Gastrointestinal tract:

• Altered gastrointestinal motility (nausea, vomiting, constipation, paralytic ileus)
• Worsening of hepatic encephalopathy

Genitourinary tract:

• Hypotonic bladder

Respiratory System:

• Respiratory acidosis secondary to respiratory muscle weakness

Endocrine System:

• Insulin resistance and impairment in insulin release

 

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References

 

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.