Derangements of Potassium Laura Medford-Davis, MD a,b, *, Zubaid Rafique, MD a,b INTRODUCTION AND PATHOPHYSIOLOGY About 98% of total body potassium (K1) is intracellular, 1,2 and 75% of the intracellular potassium is contained in skeletal muscle cells. 3,4 The body maintains the remaining 2% extracellular component within a tight range of 3.5 to 5.0 mEq/L (1 mmol equals 1 mEq K1). 3 The main mechanism for maintaining this transcellular ratio is the sodium-potassium (Na-K) adenosine triphosphatase (ATPase) pump, which uses energy in the form of adenosine triphosphate to drive K1 into cells in exchange for sodium (Na). The resulting K1 gradient creates a resting membrane potential that determines cardiac and neuromuscular cell excitability and signal conduction. a Division of Emergency Medicine, Baylor College of Medicine, 1 Baylor Plaza, Houston, TX 77030, USA; b Department of Emergency Medicine, Ben Taub General Hospital, Ben Taub General Hospital Emergency Center, 1504 Taub Loop, Houston, TX 77030, USA * Corresponding author. Department of Emergency Medicine, Ben Taub General Hospital Emergency Center, 1504 Taub Loop, Houston, TX 77030. E-mail address: medford.davis@gmail.com KEYWORDS  Potassium  Hypokalemia  Hyperkalemia  Peaked T waves KEY POINTS  Potassium balance regulates the excitability of cardiac cells, and both hypokalemia and hyperkalemia can cause cardiac arrest when severe.  Treatment of hyperkalemia includes cardiac membrane stabilization, transcellular shifting, and total body potassium elimination. Sodium bicarbonate and Kayexalate are not recom- mended for management.  Treatment of symptomatic hypokalemia consists of repletion with potassium chloride, which is available in liquid, pill, and intravenously (IV) administrable forms. Magnesium should be repleted simultaneously to potentiate potassium absorption and avoid further potassium losses.  Determine and treat the underlying cause of potassium derangement to prevent recurrence.  Avoid potentiating medications.  Consider the dietary potassium contribution.  Consider problems with potassium excretion from the gastrointestinal (GI) tract or kidneys.  Consider transcellular potassium shifts across cell membranes. Emerg Med Clin N Am 32 (2014) 329–347 http://dx.doi.org/10.1016/j.emc.2013.12.005 emed.theclinics.com 0733-8627/14/$ – see front matter Ó 2014 Elsevier Inc. All rights reserved.