Hypokalemia
972656
225186708
2008-07-12T10:16:33Z
116.0.208.29
added a link to japanese page
{{Infobox_Disease |
Name = Hypokalemia |
Image = K-TableImage.png |
Caption = [[Potassium]] |
DiseasesDB = 6445 |
ICD10 = {{ICD10|E|87|6|e|70}} |
ICD9 = {{ICD9|276.8}} |
ICDO = |
OMIM = |
MedlinePlus = 000479 |
eMedicineSubj = emerg |
eMedicineTopic = 273 |
MeshID = D007008 |
}}
'''Hypokalemia''' refers to the condition in which the concentration of [[potassium]] in the blood is low. The prefix ''hypo-'' means low (contrast with ''hyper-'', meaning high). ''Kal'' refers to ''kalium'', the [[Neo-Latin]] for potassium, and ''-emia'' means "in the blood".
Normal blood potassium levels are between 3.7 to 5.2 [[mEq]]/L<ref>http://www.nlm.nih.gov/medlineplus/ency/article/003484.htm#Normal%20Values</ref>; at least 95% of the body's potassium is found [[Intracellular|inside cells]], with the remainder in the blood. This [[concentration gradient]] is maintained principally by the [[Na+/K+-ATPase]] pump.
==Pathophysiology==
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. Decreased potassium levels in the extracellular space will cause hyperpolarization of the resting membrane potential. This [[hyperpolarization (biology)|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 in order to initiate an action potential.
In certain conditions, this will make cells less excitable. However, in the heart, it causes myocytes to become hyperexcitable. This is due to two independent effects that may lead to aberrant cardiac conduction and subsequent arrhythmia: 1) there are more inactivated sodium (Na) channels available to fire, and 2) the overall potassium permeability of the ventricle is reduced (perhaps by the loss of a direct effect of extracellular potassium on some of the potassium channels).
==Causes==
Hypokalemia can result from one or more of the following [[medical]] conditions:
* Perhaps the most obvious cause is insufficient [[eating|consumption]] of potassium (that is, a low-potassium diet). However, without excessive potassium loss from the body, this is a rare cause of hypokalemia.
* 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 [[vomiting]], [[diarrhea]], excessive [[perspiration]], or losses associated with surgical procedures
* Certain [[medication]]s can accelerate the removal of potassium from the body; including [[thiazide diuretic]]s, such as [[hydrochlorothiazide]]; [[loop diuretic]]s, such as [[furosemide]]; as well as various [[laxative]]s. The antifungal [[amphotericin B]] has also been associated with hypokalemia.
* A special case of potassium loss occurs with [[DKA|diabetic ketoacidosis]]. In addition to urinary losses from [[polyuria]] and volume contraction, there is also obligate loss of potassium from kidney tubules as a [[cationic]] partner to the negatively charged [[ketone]], β-hydroxybutyrate.
* [[Hypomagnesemia]] can cause hypokalemia. [[Magnesium]] is required for adequate processing of potassium. This may become evident when hypokalemia persists despite potassium supplementation. Other electrolyte abnormalities may also be present.
* Disease states that lead to abnormally high [[aldosterone]] levels can cause hypertension and excessive urinary losses of potassium. These include [[renal artery stenosis]] and tumors (generally non-malignant) of the [[adrenal]] glands. Hypertension and hypokalemia can also be seen with a deficiency of the 11β-hydroxylase enzyme which allows cortisols to stimulate aldosterone receptors. This deficiency can either be congenital or caused by consumption of [[glycyrrhizin]], which is contained in extract of licorice, sometimes found in [[Herbal supplements]], [[candy|candies]] and chewing tobacco.
* Rare [[hereditary]] defects of renal salt transporters, such as [[Bartter syndrome]] or [[Gitelman syndrome]] can cause hypokalemia, in a manner similar to that of diuretics. As opposed to disease states of primary excesses of aldosterone, blood pressure is either normal or low in Bartter's or Gitelman's.
* 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.
== Signs and symptoms ==
Mild hypokalemia is often without symptoms, although it may cause a small elevation of [[blood pressure]]<ref>Krishna GG et al. (1989) Increased blood pressure during potassium depletion in normotensive men. N Engl J Med., 320(18):1177-82; PMID 2624617.</ref>, and can occasionally provoke cardiac arrhythmias. Moderate hypokalemia may cause muscular weakness, [[myalgia]], and muscle cramps (owing to disturbed function of the skeletal muscles), and constipation (from disturbed function of smooth muscles). With more severe hypokalemia, flaccid [[paralysis]], [[hyporeflexia]], and [[Tetany (medical sign)|tetany]] may result. There are reports of [[rhabdomyolysis]] occurring with profound hypokalemia. [[Respiratory depression]] from severe impairment of skeletal muscle function is not uncommon.
Some electrocardiographic ([[ECG]]) findings associated with hypokalemia are flattened T waves, U waves, ST segment depression, and prolongation of the [[QT interval]].
==Treatment==
The most important step in severe hypokalemia is removing the cause, such as treating [[diarrhea]] or stopping offending medication.
Mild hypokalemia (>3.0 mEq/L) may be treated with oral potassium chloride supplements (Sando-K, Slow-K). As this is often part of a poor nutritional intake, potassium-containing foods may be recommended, such as [[tomato]]es, [[orange (fruit)|orange]]s or [[banana]]s[http://www.umassmed.edu/uploadedFiles/SourcesDietaryPotassium.pdf]. Both dietary and pharmaceutical supplements are used for people taking diuretic medications (see '''Causes''', above).
Severe hypokalemia (<3.0 mEq/L) may require [[intravenous]] supplementation. Typically, [[saline (medicine)|saline]] is used, with 20-40 mEq KCl per liter over 3-4 hours. Giving intravenous potassium at faster rates may predispose to [[ventricular tachycardia]]s and requires intensive monitoring.
Difficult or resistant cases of hypokalemia may be amenable to a potassium-sparing [[diuretic]] such as [[amiloride]], [[triamterene]], or [[spironolactone]]. In contrast to the more commonly used [[diuretics]] like [[HCTZ|hydrochlorothiazide]] and [[furosemide]], these potassium-sparing diuretics actually reduce the kidney's excretion of potassium.
When replacing potassium intravenously, infusion via [[Central venous catheter|central line]] is encouraged to avoid the frequent occurrence of a burning sensation at the site of a peripheral IV, 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 IV fluid, or mixing 3 ml of 1% lidocaine to each 10 meq of kcl per 50 ml of IV fluid. The practice of adding lidocaine, however, raises the likelihood of serious medical errors.[http://www.ismp.org/newsletters/acutecare/articles/20040212_2.asp]
==Hypokalemia in pets==
Cats can develop hypokalemia in old age, but Burmese kittens may be genetically prone to the condition if both parents have a defective gene. Symptoms are: staggering, an inability to keep up head which droops alarmingly and animals have good appetite but fail to gain weight. Treatment can include adding ground potassium chloride tablets to the animal's food.<ref>Feline Hypokalemic Polymyopathy. in The Merck Veterinary Manual, 9th edition By Merck & Co. 2006. ISBN 0-911910-50-6</ref>
==See also==
* [[Hypomagnesemia]]
* [[Potassium deficiency (plant disorder)]]
* [[Hyperkalemia]]
== External links ==
* [http://www.nal.usda.gov/fnic/foodcomp/Data/SR20/nutrlist/sr20w306.pdf Content of Selected Foods per Common Measure, sorted by nutrient content (Potassium)]
:USDA National Nutrient Database for Standard Reference, Release 20]
* [http://www.umassmed.edu/uploadedFiles/SourcesDietaryPotassium.pdf List of foods rich in potassium (U. Mass. Med.)]
==References==
<references/>
* Kasper DL ''et al'' (Eds). ''[[Harrison's Principles of Internal Medicine]]'', 16th ed, chapter 41, pages 258-61. ISBN 0-07-140235-7.
* Rose, B.D. and T.W. Post, ''Clinical Physiology of Acid-Base and Electrolyte Disorders'', 5th ed. 2001, pages 836-887. ISBN 0-07-134682-1
{{Fluid, electrolyte, acid base metabolic pathology}}
[[Category:Endocrinology]]
[[Category:Nephrology]]
[[Category:Electrolyte disturbances]]
[[Category:Potassium]]
[[de:Hypokaliämie]]
[[es:Hipopotasemia]]
[[fr:Hypokaliémie]]
[[it:Ipokaliemia]]
[[ja:低カリウム血症]]
[[pl:Hipokaliemia]]
[[pt:Hipocaliémia]]
[[ru:Гипокалиемия]]
[[sv:Hypokalemi]]
[[vi:Hạ kali máu]]