Hypokalemia

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Hypokalemia
Classification and external resources
LowKECG.JPG
An ECG in a person with a potassium level of 1.1 showing the classical ECG changes of ST segment depression, inverted T waves, large U waves, and a slightly prolonged PR interval
ICD-10 E87.6
ICD-9 276.8
DiseasesDB 6445
MedlinePlus 000479
eMedicine article/242008 emerg/273
Patient UK Hypokalemia
MeSH D007008

Hypokalemia (American English) or hypokalaemia (British English), also hypopotassemia or hypopotassaemia (ICD-9), refers to the condition in which the concentration of potassium (K+) in the blood is low. The prefix hypo- means "under" (contrast with hyper-, meaning "over"); kal- refers to kalium, the Neo-Latin for potassium, and -emia means "condition of the blood."

Normal plasma potassium levels are between 3.5 and 5.0 meq/l;[1] about 98% of the body's potassium is found inside cells, with the remainder in the extracellular fluid including the blood. Alternately, the NIH denotes 3.7–5.2 meq/l as a normal range.[2] This concentration gradient is maintained principally by the Na+/K+ pump.

Signs and symptoms[edit]

Mild hypokalemia is often without symptoms, although it may cause a small elevation of blood pressure,[3] and can occasionally provoke the development of an abnormal heart rhythm. Severe hypokalemia, with serum potassium concentrations of 2.5–3 meq/l (Nl: 3.5–5.0 meq/l), may cause muscle weakness, myalgia, and muscle cramps (owing to disturbed function of skeletal muscle), and constipation (from disturbed function of smooth muscle). With more severe hypokalemia, flaccid paralysis and hyporeflexia may result. Reports exist of rhabdomyolysis occurring with profound hypokalemia with serum potassium levels less than 2 meq/l.[citation needed] Respiratory depression from severe impairment of skeletal muscle function is found in many patients.[citation needed]

Some electrocardiographic (ECG) findings associated with hypokalemia include flattened or inverted T waves, a U wave, ST depression, and a wide PR interval. Due to prolonged repolarization of ventricular Purkinje fibers, a prominent U wave occurs, frequently superimposed upon the T wave and therefore produces the appearance of a prolonged QT interval.[4]

Causes[edit]

Hypokalemia can result from one or more of these medical conditions:

Inadequate potassium intake[edit]

Perhaps the most obvious cause is insufficient consumption of potassium (that is, a low-potassium diet) or starvation. However, without excessive potassium loss from the body, this is a rare cause of hypokalemia.

Gastrointestinal/integument loss[edit]

A more common cause is excessive loss of potassium, often associated with heavy fluid losses that "flush" potassium out of the body. Typically, this is a consequence of diarrhea, excessive perspiration, or losses associated with surgical procedures. Vomiting can also cause hypokalemia, although not much potassium is lost from the vomitus. Rather, heavy urinary losses of K+ in the setting of postemetic bicarbonaturia force urinary potassium excretion (see Alkalosis below). Other GI causes include pancreatic fistulae and the presence of adenoma.

Urinary loss[edit]

Distribution away from ECF[edit]

  • In addition to alkalosis, other factors can cause transient shifting of potassium into cells, presumably by stimulation of the Na+/K+ pump.[5] These hormones and medications include insulin, epinephrine, and other beta agonists (e.g. salbutamol or salmeterol), and xanthines (e.g. theophylline).[7]
  • Rare hereditary defects of muscular ion channels and transporters that cause hypokalemic periodic paralysis can precipitate occasional attacks of severe hypokalemia and muscle weakness. These defects cause a heightened sensitivity to the normal changes in potassium produced by catechols and/or insulin and/or thyroid hormone, which lead to movement of potassium from the extracellular fluid into the muscle cells.

Other[edit]

  • A handful of published reports describe individuals with severe hypokalemia related to chronic extreme consumption (4–10 l/day) of colas.[8] The hypokalemia is thought to be from the combination of the diuretic effect of caffeine[9] and copious fluid intake, although it may also be related to diarrhea caused by heavy fructose ingestion.[10][11] A physiological response to hypercapnia, blood potassium (as well as calcium) helps offset acidosis, which is consistent with chronic, extreme consumption of carbonated beverages.

Pseudohypokalemia[edit]

  • Pseudohypokalemia is a decrease in the amount of potassium that occurs due to excessive uptake of potassium by metabolically active cells in a blood sample after it has been drawn. It is a laboratory artifact that may occur when blood samples remain in warm conditions for several hours before processing.[12]

Pathophysiology[edit]

Potassium is essential for many body functions, including muscle and nerve activity. The electrochemical gradient of potassium between the intracellular and extracellular space is essential for nerve function; in particular, potassium is needed to repolarize the cell membrane to a resting state after an action potential has passed. Lower potassium levels in the extracellular space cause hyperpolarization of the resting membrane potential. This hyperpolarization is caused by the effect of the altered potassium gradient on resting membrane potential as defined by the Goldman equation. As a result, a greater than normal stimulus is required for depolarization of the membrane to initiate an action potential.

In the heart, hypokalemia causes hyperpolarization in the myocytes' resting membrane potential. The more negative membrane potentials in the atrium may cause arrhythmias because of more complete recovery from sodium-channel inactivation, making the triggering of an action potential less likely. In addition, the reduced extracellular potassium (paradoxically) inhibits the activity of the IKr potassium current[13] and delays ventricular repolarization. This delayed repolarization may promote reentrant arrhythmias.

Treatment[edit]

The most important treatment in severe hypokalemia is addressing the cause, such as improving the diet, treating diarrhea, or stopping an offending medication. Patients without a significant source of potassium loss and who show no symptoms of hypokalemia may not require treatment.

Mild hypokalemia (>3.0 meq/l) may be treated with oral potassium chloride supplements (Klor-Con, Sando-K, Slow-K). As this is often part of a poor nutritional intake, potassium-containing foods may be recommended, such as leafy green vegetables, tomatoes, coconut water, citrus fruits, oranges, or bananas.[14] Both dietary and pharmaceutical supplements are used for people taking diuretic medications.

Severe hypokalemia (<3.0 meq/l) may require intravenous supplementation. Typically, a saline solution is used, with 20–40 meq/l KCl per liter over 3–4 hours. Giving IV potassium at faster rates (20–25 meq/hr) may predispose to ventricular tachycardias and requires intensive monitoring. A generally safe rate is 10 meq/hr. Even in severe hypokalemia, oral supplementation is preferred given its safety profile. Sustained-release formulations should be avoided in acute settings.

Difficult or resistant cases of hypokalemia may be amenable to a potassium-sparing diuretic, such as amiloride, triamterene, spironolactone, or eplerenone. Concomittant hypomagnesemia will inhibit potassium replacement, as magnesium is a cofactor for potassium uptake.[15]

When replacing potassium intravenously, infusion by a central line is encouraged to avoid the frequent occurrence of a burning sensation at the site of a peripheral infusion, or the rare occurrence of damage to the vein. When peripheral infusions are necessary, the burning can be reduced by diluting the potassium in larger amounts of fluid, or mixing 3 ml of 1% lidocaine to each 10 meq of KCl per 50 ml of fluid. The practice of adding lidocaine, however, raises the likelihood of serious medical errors.[16]

See also[edit]

References[edit]

  1. ^ Kratz, A; Ferraro, M; Sluss, PM; Lewandrowski, KB; Ellender, Stacey M.; Peters, Christine C.; Kratz, Alexander; Ferraro, Maryjane; Sluss, Patrick M.; Lewandrowski, Kent B. (2004). "Case records of the Massachusetts General Hospital. Weekly clinicopathological exercises. Laboratory reference values". The New England Journal of Medicine 351 (15): 1548–63. doi:10.1056/NEJMcpc049016. PMID 15470219. 
  2. ^ Dugdale, David. "MedlinePlus: Potassium Test". Retrieved 12 January 2013. 
  3. ^ Krishna, GG; Miller, E; Kapoor, S (1989). "Increased blood pressure during potassium depletion in normotensive men". The New England Journal of Medicine 320 (18): 1177–82. doi:10.1056/NEJM198905043201804. PMID 2624617. 
  4. ^ Goldman, M.J. (1973). Principles of Clinical Electrocardiography 8th ed. Los Altos, California: LANGE medical Publications. p. 293. 
  5. ^ a b Halperin, ML; Kamel, KS (1998). "Potassium". Lancet 352 (9122): 135–40. doi:10.1016/S0140-6736(98)85044-7. PMID 9672294. 
  6. ^ Walmsley RN, White GH (August 1984). "Occult causes of hypokalaemia". Clin. Chem. 30 (8): 1406–8. PMID 6744598. 
  7. ^ Whyte KF, Addis GJ, Whitesmith R, Reid JL (April 1987). "Failure of chronic theophylline therapy to alter circulating catecholamines". Eur J Respir Dis 70 (4): 221–8. PMID 3582518. 
  8. ^ Tsimihodimos V, Kakaidi V, & Elisaf M. (June 2009). "Cola-induced hypokalaemia: pathophysiological mechanisms and clinical implications". International Journal of Clinical Practice 63 (6): 900–2. doi:10.1111/j.1742-1241.2009.02051.x. PMID 19490200. 
  9. ^ Shirley DG, Walter SJ, Noormohamed FH (November 2002). "Natriuretic effect of caffeine: assessment of segmental sodium reabsorption in humans". Clin. Sci. 103 (5): 461–6. doi:10.1042/CS20020055. PMID 12401118. 
  10. ^ Packer, C.D. (June 2009). "Cola-induced hypokalaemia: a super-sized problem". International Journal of Clinical Practice 63 (6): 833–5. doi:10.1111/j.1742-1241.2009.02066.x. PMID 19490191. 
  11. ^ By HealthGuru (2012-03-01). "Health.yahoo.com". Health.yahoo.com. Retrieved 2012-03-10. 
  12. ^ Sodi R, Davison AS, Holmes E, Hine TJ, Roberts NB (June 2009). "The phenomenon of seasonal pseudohypokalemia: effects of ambient temperature, plasma glucose and role for sodium-potassium-exchanging-ATPase". Clin. Biochem. 42 (9): 813–8. doi:10.1016/j.clinbiochem.2009.01.024. PMID 19232334. 
  13. ^ Sanguinetti, MC; Jurkiewicz, NK (February 1992). "Role of external Ca2+ and K+ in gating of cardiac delayed rectifier K+ currents". Pflugers Archiv : European journal of physiology 420 (2): 180–6. doi:10.1007/BF00374988. PMID 1620577. 
  14. ^ "Sources of Dietary Protein" (PDF). University of Massachusetts Medical School. Retrieved 2012-03-10. 
  15. ^ "New Guidelines for Potassium Replacement in Clinical Practice". Retrieved 2011-02-16. 
  16. ^ "Safety Issues With Adding Lidocaine to IV Potassium Infustions (Excerpt)". Retrieved 2009-05-09. 

Further reading[edit]

External links[edit]