18 Hypokalemia

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<p>S. Faubel and J. Topf</p> <p>18 Hypokalemia</p> <p>18 Hypokalemia</p> <p>18</p> <p>485</p> <p>The Fluid, Electrolyte and Acid-Base Companion</p> <p>Introduction tration.+</p> <p>Hypokalemia is a low plasma potassium concenK+K++</p> <p>K</p> <p>K</p> <p>Na Cl K+ HCO+ </p> <p>3</p> <p>BUN glucose</p> <p>CreatinineK+</p> <p>K</p> <p>+</p> <p>Hypokalemia is defined as a plasma potassium concentration less than 3.5 mEq/L.</p> <p>Because potassium is necessary for muscle activity and rhythmic cardiac contraction, recognizing hypokalemia is important. Hypokalemia is a common clinical problem which is often iatrogenic.</p> <p>Hypokalemia is a ____________ electrolyte disorder which is often __________.</p> <p>486</p> <p>K+</p> <p>common iatrogenic</p> <p>S. Faubel and J. Topf</p> <p>18 Hypokalemia</p> <p>Etiologies Hypokalemia is due to either decreased intake or increased loss of potassium.DECREASED INTAKE INCREASED LOSS EXTRA - RENAL RENAL</p> <p>K</p> <p>+</p> <p>K</p> <p>+</p> <p>+</p> <p>K</p> <p>K</p> <p>+</p> <p>K</p> <p>+</p> <p>There are two primary causes of hypokalemia: decreased intake of potassium increased loss of potassium Decreased intake of potassium is an uncommon cause of hypokalemia because almost all diets are rich in potassium. Increased potassium loss is either from an extra-renal or renal source.</p> <p>Hypokalemia is due to either decreased potassium __________ or increased potassium ______.</p> <p>Potassium losses are divided into renal and _________ sources.</p> <p>extra-renal</p> <p>intake loss</p> <p>487</p> <p>K+++</p> <p>K</p> <p>K</p> <p>The Fluid, Electrolyte and Acid-Base Companion</p> <p>Etiologies Decreased intake Decreased intake of potassium is an uncommon cause of hypokalemia.One large banana provides about 10 mEq of potassium.</p> <p>K</p> <p>+</p> <p>The healthy kidney is able to reduce potassium loss to 5 mEq a day.</p> <p>Poor dietary intake of potassium is an uncommon cause of hypokalemia because most diets are rich in potassium. In addition, the kidney is usually able to compensate for a low potassium diet by reducing potassium loss to as low as 5 mEq per day. Potassium is found in practically all foods: fruits, meats, vegetables and milk. A lack of potassium in the diet is usually secondary to a lack of food in general.</p> <p>Alcoholics are notorious for poor eating habits and are prone to a variety of nutritional deficiencies including hypokalemia. Other patients prone to inadequate dietary intake are the elderly, the poor and patients with anorexia nervosa. People using liquid diets for quick weight loss may develop profound hypokalemia.</p> <p>Dietary deficiency of potassium is a(n) _______ cause of hypokalemia. Alcohol is _____ a good source of potassium. The kidney is good at minimizing _________ loss.</p> <p>uncommon potassium not</p> <p>488</p> <p>S. Faubel and J. Topf</p> <p>18 Hypokalemia</p> <p>What is your name?</p> <p>King Arthur. King of the Britons.</p> <p>What is your quest ? I seek the holy Grail. What is the electrolyte disorder associated with chronic clay ingestion ? Grey clay or red clay? I dont know that . . . arrrggghhhSome communities in the Southeastern United States ingest clay as part of their diet. The ingestion of grey clay acts as a potassium and iron binder, preventing their absorption from the digestive tract. This can result in hypokalemia and anemia over time.</p> <p>On the other hand, red clay is rich in potassium. People who eat red clay can become dangerously hyperkalemic if they have concurrent renal insufficiency.</p> <p>489</p> <p>The Fluid, Electrolyte and Acid-Base Companion</p> <p>Etiologies Increased loss The vast majority of cases of hypokalemia are due to the loss of potassium.K+</p> <p>K</p> <p>+</p> <p>+</p> <p>K</p> <p>K</p> <p>+</p> <p>K</p> <p>+</p> <p>Movement into cellsinsulin catecholamines alkalemia pseudohypokalemia periodic paralysis</p> <p>GI lossdiarrhea vipoma colonic fistulas surgical drains villous adenoma</p> <p>Renal lossdiuretics Bartters syndrome Gitelmans syndrome primary hyperaldosteronism renovascular hypertension Cushings syndrome pseudohyperaldosteronism congenital adrenal hyperplasia diabetic ketoacidosis vomiting renal tubular acidosis penicillin toluene</p> <p>Increased potassium loss is the most common cause of hypokalemia. Hypokalemia can be due to the movement of potassium into cells or the loss of potassium from the GI tract or from the kidney.</p> <p>Each of these three sources of potassium loss is discussed in detail on the following pages.</p> <p>Diuretics are a cause of ___________ potassium loss.</p> <p>Movement of potassium into ______ is a type of extra-renal loss of potassium that can cause hypokalemia.</p> <p>490</p> <p>K+++</p> <p>K</p> <p>K</p> <p>renal cells</p> <p>S. Faubel and J. Topf</p> <p>18 Hypokalemia</p> <p>Etiologies Increased loss Movement into cells The shift of extracellular potassium into cells can cause hypokalemia.KK+</p> <p>+</p> <p>cell construction</p> <p>alkalemia</p> <p>increased insulinK+</p> <p>pseudohypokalemia</p> <p>K+</p> <p>periodic paralysis</p> <p>Hypokalemia can be due to the movement of potassium into cells. In this situation, the plasma potassium is low, but total body potassium can be normal. This type of hypokalemia is referred to as redistribution hypokalemia. Movement of potassium into cells can be caused by: alkalemia insulin catecholamines periodic paralysis pseudohypokalemia cell construction (e.g., treatment of severe megaloblastic anemia)</p> <p>In redistribution hypokalemia, total body potassium can be ________ despite a low plasma potassium.</p> <p>K</p> <p>+</p> <p>catecholamines</p> <p>K</p> <p>+</p> <p>extracellular normal</p> <p>491</p> <p>The Fluid, Electrolyte and Acid-Base Companion</p> <p>Etiologies Increased loss Movement into cells Alkalemia causes cells to release hydrogen and absorb potassium.</p> <p>K+</p> <p>pHH+</p> <p>K+</p> <p>K+</p> <p>One of the immediate safeguards against alkalemia (decreased H+ concentration) is the movement of hydrogen out of the cells. As hydrogen leaves, potassium enters the cell in order to maintain electroneutrality.</p> <p>The effect of alkalemia on plasma potassium is minor, but does occur in both respiratory and metabolic alkalosis.</p> <p>An increase in pH will cause extracellular ___________ to move into the intracellular compartment in exchange for ___________.</p> <p>potassium hydrogen</p> <p>492</p> <p>S. Faubel and J. Topf</p> <p>18 Hypokalemia</p> <p>Etiologies Increased loss Movement into cells Insulin causes the movement of glucose and potassium into cells.insulin</p> <p>K+</p> <p>K</p> <p>+</p> <p>2 K+</p> <p>insulin receptor</p> <p>ATP AMP 3 Na+</p> <p>Insulin affects the movement of potassium into cells by stimulating the Na-K-ATPase pump. Below are two scenarios in which insulin-induced potassium shifts are clinically relevant:</p> <p>Treatment of diabetic ketoacidosis. DKA is due to a lack of insulin and characterized by ketoacidosis, hyperglycemia and potassium depletion. Although total body potassium is decreased, plasma potassium is usually increased because of the lack of insulin. Treatment with insulin moves potassium into cells, causing hypokalemia. In a patient with DKA, hypokalemia at presentation signifies dangerous potassium depletion. In this situation, potassium should be replaced prior to initiating insulin therapy.</p> <p>Treatment of hyperkalemia. The ability of insulin to cause the movement of potassium into cells is used to advantage in the treatment of acute hyperkalemia.The mechanism of potassium depletion in DKA is reviewed later in this chapter . DKA is reviewed in Chapter 13, Anion Gap Metabolic Acidosispage 342.</p> <p>Insulin drives glucose and _________ into cells.</p> <p>In diabetic ketoacidosis, __________ therapy can cause hypokalemia.</p> <p>potassium</p> <p>insulin</p> <p>493</p> <p>The Fluid, Electrolyte and Acid-Base Companion</p> <p>Etiologies Increased loss Movement into cells amines cause the movement of potassium into cells.catecholamines</p> <p>Catechol-</p> <p>K+</p> <p>K</p> <p>+</p> <p>2 K+</p> <p>-2 receptor</p> <p>ATP AMP 3 Na+</p> <p>Catecholamines act at beta-2 receptors to stimulate Na-K-ATPase activity, facilitating the movement of potassium into cells. Both endogenous and exogenous catecholamines can cause hypokalemia through intracellular redistribution. Endogenous catecholamines are released during stress. An exogenous adrenergic agonist is albuterol which is used in the treatment of asthma. As in other causes of redistribution hypokalemia, the effect of catecholamines on plasma potassium is only significant in situations where potassium concentration is already low. For example, because alcoholics are typically hypokalemic at base line, the catecholamine surge from delirium tremens (alcohol withdrawal) can precipitate severe hypokalemia. Redistribution hypokalemia from catecholamines may also play a role in some cases of sudden cardiac death associated with diuretics. Diuretics can cause mild hypokalemia which can become severe in the face of catecholamine release from a stressful event. The further lowering of plasma potassium from catecholamine release can trigger a lethal cardiac arrhythmia.Catecholamines bind to _________ receptors which stimulate the activity of the _________ pump.</p> <p>In addition to endogenous catecholamines, drugs which bind beta-2 receptors can cause ___________ to move into the cells.</p> <p>beta-2 Na-K-ATPase potassium</p> <p>494</p> <p>S. Faubel and J. Topf</p> <p>18 Hypokalemia</p> <p>Etiologies Increased loss Movement into cells paralysis is a rare cause of hypokalemia.Triggers of hypokalemia</p> <p>PeriodicEffects</p> <p>temperature dysregulationK+</p> <p>+</p> <p>K</p> <p>+</p> <p>K</p> <p>K</p> <p>+</p> <p>paralysis increased insulin+</p> <p>K</p> <p>+</p> <p>K</p> <p>pHalkalemia</p> <p>+</p> <p>K</p> <p>+</p> <p>K</p> <p>sudden cardiac deathK++</p> <p>137 108 1.2 32</p> <p>Hypokalemic periodic paralysis is a rare condition in which the movement of extracellular potassium into cells causes paralysis. It is the most common member of a family of diseases called familial periodic paralysis. This family of diseases is characterized by recurrent, transient attacks of muscle weakness.</p> <p>excessive exercise</p> <p>Hypokalemic episodes can be triggered by meals high in carbohydrates (insulin release), exercise, temperature extremes and stress. All of these triggers cause mild and transient hypokalemia in normal patients, but cause severe hypokalemia in patients with periodic paralysis. Paralysis typically affects the lower extremities and moves proximally, sparing the cranial nerves. The risk of sudden cardiac death and malignant hyperthermia is increased in patients with periodic paralysis. Hypokalemic periodic paralysis is inherited in an autosomal dominant fashion with complete penetrance. Since sporadic cases can occur, a lack of family history does not rule out the diagnosis. The first attack typically occurs before the age of twenty. After the initial presentation, attacks become more frequent until decreasing in frequency after age thirty.</p> <p>This disease has recently been mapped to the long arm of chromosome one and it appears that at least some cases have a defect in a calcium channel protein. Currently it is unknown how a defect in a calcium channel could result in hypokalemia, though a defect in calcium release from the sarcoplasmic reticulum could explain paralysis.Hypokalemic periodic paralysis is a ______ (rare/common) disorder. rare</p> <p>K</p> <p>+</p> <p>K</p> <p>K+</p> <p>severe hypokalemia</p> <p>495</p> <p>The Fluid, Electrolyte and Acid-Base Companion</p> <p>Clinical correlation: Movement of potassium into cells while in the collection tube causes pseudohypokalemia.</p> <p>Occasionally, patients with leukemia who have extremely high white blood cell counts can have potassium measurements less than 1.0 mEq/ L, although the true plasma concentration is actually normal. This artifactual measurement of potassium is known as pseudohypokalemia. Pseudohypokalemia occurs because the WBCs of the blood sample remain metabolically active after being drawn into collection tubes. In the tube, the WBCs continue to pump extracellular potassium into the cells through the action of the Na-K-ATPase pump. There are two methods of obtaining an accurate plasma potassium measurement in the face of an extremely high WBC count: Immediately chill the blood sample (slows metabolism). Immediately centrifuge the blood specimen to separate the plasma from the WBCs prior to measurement.</p> <p>Leukocytosis can also cause pseudo hyperkalemia. The mechanism of this phenomenon is reviewed in Chapter 19, Hyperkalemiapage 551.</p> <p>496</p> <p>S. Faubel and J. Topf</p> <p>18 Hypokalemia</p> <p>Etiologies Increased loss GI Hypokalemia from lower gastrointestinal losses is found with massive diarrhea.</p> <p>+</p> <p>K</p> <p>GI loss of potassiumdiarrhea vipoma colonic fistulas surgical drains villous adenoma</p> <p>K</p> <p>+</p> <p>Normally, only 10 to 15 mEq/L of potassium are lost in the stool per day. Disorders which increase GI fluid loss increase the loss of potassium and predispose to hypokalemia. Diarrhea is the most common cause of excess GI potassium loss. Cholera causes massive diarrhea which results in GI potassium losses up to ten-times normal. Vipomas are colonic tumors that secrete potassium-rich fluid into the colon which can cause daily potassium loss of up to 300 mEq. Patients with this disorder can become critically ill and often have hypovolemic shock.</p> <p>Vomiting causes hypokalemia whichnot due to the loss of potassium from the GI tract. is Vomiting increases the excretion of potassium; the mechanism is reviewed later in this renal chapter on page 520.Normally only a ______ amount of potassium is lost in the stool. In some situations, GI potassium loss can be magnified by profuse diarrhea as found in _________ or vipoma. Vomiting causes hypokalemia by increasing the _______ excretion of potassium. small cholera</p> <p>+</p> <p>K</p> <p>renal</p> <p>497</p> <p>The Fluid, Electrolyte and Acid-Base Companion</p> <p>Etiologies Increased loss Renal Renal potassium loss is the most common cause of clinically significant hypokalemia.</p> <p>Renal loss of potassiumIncreased distal flow diuretics Bartters syndrome Gitelmans syndrome Increased mineralocorticoid activity primary hyperaldosteronism Cushings syndrome congenital adrenal hyperplasia hyperreninism pseudohyperaldosteronism Nonresorbable anions in the distal tubule diabetic ketoacidosis vomiting renal tubular acidosis penicillin derivatives toluene</p> <p>K</p> <p>+</p> <p>K</p> <p>+</p> <p>Renal loss of potassium leading to hypokalemia is due to increased secretion of potassium in the distal nephron. This occurs in three situations: increased distal flow increased mineralocorticoid activity nonresorbable anions in the distal tubule</p> <p>As reviewed in Chapter 17, Introduction to Potassium distal nephron is the most impor, the tant part of the nephron in regards to potassium regulation. effects of distal flowinThe , creased mineralocorticoid activity and nonresorbable anions are reviewed beginning on page 478.Increased renal loss of potassium is due to increased potassium secretion by the distal ________. Three conditions increase potassium secretion: increased _________ flow increased _____________ activity non-__________ anions in the distal tubule secretion nephron distal mineralocorticoid resorbable</p> <p>498</p> <p>K++</p> <p>K</p> <p>S. Faubel and J. Topf</p> <p>18 Hypokalemia</p> <p>Etiologies Increased loss Renal Distal flow Loop and thiazide diuretics cause hypokalemia by increasing distal flow.</p> <p>K</p> <p>+</p> <p>K</p> <p>+</p> <p>Increased flow...</p>