Medical School · Year 3 · Internal Medicine · includes a discussion video

Seminar 13: Electrolyte Disorders

Internal Medicine Clerkship

Learning Objectives

By the end of this seminar, students will be able to:

1. Recognize the clinical manifestations of major electrolyte disorders across the severity spectrum and identify when urgent intervention is required
2. Describe the systematic diagnostic approach to hyponatremia including assessment of osmolality, volume status, and urine studies
3. Apply appropriate treatment strategies for sodium disorders while adhering to safe correction rates to prevent osmotic demyelination syndrome
4. Manage both hypokalemia and hyperkalemia with an understanding of transcellular shifts, definitive treatment, and ECG monitoring
5. Describe the pathophysiology, differential diagnosis, and management of calcium and magnesium disorders
6. Recognize critical electrolyte emergencies requiring immediate stabilization and continuous cardiac monitoring

Seminar Outline

Section 1: Sodium Disorders - Overview

Sodium is the primary cation of the extracellular fluid compartment and is the major determinant of serum osmolality and extracellular fluid volume. The normal serum sodium concentration is maintained within a narrow range of one hundred thirty-five to one hundred forty-five milliequivalents per liter through the coordinated actions of multiple regulatory systems. Total body sodium content determines extracellular fluid volume, while serum sodium concentration reflects the balance between total body sodium and total body water. The distinction between sodium content and sodium concentration is clinically critical: disorders of sodium concentration are fundamentally disorders of water balance rather than sodium balance, and this concept underpins the diagnostic and therapeutic approach to both hyponatremia and hypernatremia.

The regulation of sodium and water balance involves three principal hormonal systems. Antidiuretic hormone, also known as arginine vasopressin, is secreted by the posterior pituitary in response to increased serum osmolality or decreased effective circulating volume, and it acts on the collecting duct of the kidney to promote water reabsorption, thereby diluting the serum sodium concentration. The renin-angiotensin-aldosterone system responds to decreased renal perfusion pressure and stimulates sodium reabsorption in the distal nephron, thereby retaining sodium and expanding extracellular volume. The thirst mechanism is activated by increased serum osmolality and serves as the primary defense against hypernatremia by driving water intake. The interplay of these three systems maintains serum osmolality, calculated as two times the serum sodium plus blood urea nitrogen divided by 2.8 plus glucose divided by eighteen, within the normal range of two hundred eighty to two hundred ninety-five milliosmoles per kilogram.

Hyponatremia, defined as a serum sodium concentration below one hundred thirty-five milliequivalents per liter, is the most common electrolyte disorder encountered in hospitalized patients. The severity of hyponatremia is graded as mild (sodium one hundred thirty to one hundred thirty-four), moderate (sodium one hundred twenty-five to one hundred twenty-nine), and severe (sodium less than one hundred twenty-five milliequivalents per liter). The chronicity of hyponatremia is a critical determinant of both symptom severity and treatment urgency: acute hyponatremia, developing over less than forty-eight hours, is more likely to be symptomatic and carries a higher risk of cerebral edema, while chronic hyponatremia, developing over more than forty-eight hours, allows for cerebral adaptation through extrusion of intracellular osmolytes and is more likely to be asymptomatic or mildly symptomatic.

The clinical manifestations of hyponatremia correlate with both the severity and the rate of development. Mild hyponatremia is often asymptomatic or produces only subtle symptoms such as fatigue and difficulty with concentration. Moderate hyponatremia may cause nausea, headache, confusion, and gait instability. Severe hyponatremia, particularly when acute, can produce life-threatening neurological symptoms including seizures, obtundation, coma, and transtentorial herniation due to cerebral edema resulting from the osmotic movement of water into brain cells. Acute hyponatremia tends to produce more severe symptoms at any given sodium level because the brain has not had sufficient time to adapt through compensatory osmolyte extrusion. Chronic hyponatremia, while less acutely dangerous, is associated with increased fall risk, cognitive impairment, osteoporosis, and bone fractures, highlighting the importance of treatment even when symptoms are mild.

<image>Panel A: Diagram of sodium physiology showing sodium as the major extracellular cation with normal range 135-145 mEq/L, illustrating the relationship between total body sodium (determines ECF volume) and serum sodium concentration (reflects water balance), with the kidney as the central regulatory organ. Panel B: Illustration of three regulatory systems: ADH pathway from hypothalamus to posterior pituitary to collecting duct (water reabsorption), RAAS pathway from juxtaglomerular apparatus through renin, angiotensin II, to aldosterone (sodium reabsorption), and thirst mechanism (water intake), converging on serum osmolality homeostasis. Panel C: Hyponatremia severity scale showing mild (130-134), moderate (125-129), and severe (<125) with color-coded zones, alongside acute versus chronic timeline showing cerebral adaptation through osmolyte extrusion over 48 hours. Panel D: Clinical manifestation spectrum from mild (asymptomatic, fatigue) through moderate (nausea, headache, confusion) to severe (seizures, coma, herniation), with brain cross-sections showing progressive cerebral edema at each severity level.</image>

Section 2: Hyponatremia Approach

The diagnostic approach to hyponatremia follows a systematic three-step algorithm that efficiently narrows the differential diagnosis. The first step is to assess the serum osmolality, which categorizes hyponatremia into three groups. Hypotonic hyponatremia, with a serum osmolality below two hundred eighty milliosmoles per kilogram, represents true hyponatremia with excess water relative to sodium and accounts for the vast majority of cases. Isotonic hyponatremia, also called pseudohyponatremia, occurs when elevated concentrations of lipids or proteins in the serum displace water in laboratory assays that measure sodium in the total sample volume rather than the aqueous phase, yielding a spuriously low sodium concentration; this is a laboratory artifact that does not require treatment. Hypertonic hyponatremia occurs when elevated concentrations of osmotically active solutes, most commonly glucose in hyperglycemia, draw water from the intracellular to the extracellular compartment, diluting the serum sodium; the corrected sodium can be estimated by adding 1.6 to 2.4 milliequivalents per liter for every one hundred milligrams per deciliter increase in glucose above normal.

The second step in the diagnostic algorithm is to assess the patient's volume status, which divides hypotonic hyponatremia into three categories based on total body sodium and water. Hypovolemic hyponatremia occurs when both sodium and water are lost but sodium loss exceeds water loss, as seen in gastrointestinal losses from vomiting and diarrhea, renal losses from diuretic use, and third-spacing of fluid. Euvolemic hyponatremia occurs when total body water is increased with relatively normal total body sodium, as seen in the syndrome of inappropriate antidiuretic hormone secretion, hypothyroidism, and adrenal insufficiency. Hypervolemic hyponatremia occurs when both total body sodium and water are increased but water retention is disproportionately greater, as seen in congestive heart failure, cirrhosis, and nephrotic syndrome, all of which are characterized by decreased effective circulating volume that stimulates ADH secretion and water retention.

The third step is to evaluate urine studies, which provide critical information about the kidney's response to the hyponatremic state. A urine sodium concentration below twenty milliequivalents per liter indicates that the kidney is appropriately retaining sodium in response to decreased effective circulating volume, as seen in hypovolemic hyponatremia from extrarenal causes and hypervolemic states such as heart failure and cirrhosis. A urine sodium concentration above forty milliequivalents per liter indicates renal sodium wasting or is characteristic of SIADH, where the kidneys excrete sodium normally despite the presence of hyponatremia. Urine osmolality below one hundred milliosmoles per kilogram indicates maximally dilute urine and suggests primary polydipsia, in which excess water intake overwhelms the kidney's diluting capacity. Urine osmolality above one hundred milliosmoles per kilogram indicates the presence of antidiuretic hormone activity, whether appropriate (as in hypovolemia) or inappropriate (as in SIADH).

The syndrome of inappropriate antidiuretic hormone secretion is the most common cause of euvolemic hyponatremia and has specific diagnostic criteria that must be satisfied. The serum sodium must be less than one hundred thirty-five milliequivalents per liter with a corresponding serum osmolality below two hundred seventy-five milliosmoles per kilogram, confirming true hypotonic hyponatremia. The urine must be inappropriately concentrated with an osmolality above one hundred milliosmoles per kilogram, and the urine sodium must be above forty milliequivalents per liter, reflecting normal renal sodium handling in the absence of volume depletion. The patient must be clinically euvolemic, without evidence of edema or volume depletion. Importantly, hypothyroidism and adrenal insufficiency must be excluded, as both conditions can mimic SIADH and require specific treatment. Common causes of SIADH include central nervous system disorders (stroke, hemorrhage, tumors, meningitis), pulmonary diseases (pneumonia, tuberculosis, small cell lung cancer), medications (carbamazepine, SSRIs, cyclophosphamide), and the postoperative state, particularly after major surgery with significant pain and narcotic use.

<image>Panel A: Three-step diagnostic algorithm for hyponatremia displayed as a decision tree: Step 1 assessing serum osmolality (hypotonic, isotonic/pseudohyponatremia, hypertonic), Step 2 assessing volume status (hypovolemic, euvolemic, hypervolemic) with clinical examples, and Step 3 evaluating urine studies to confirm the diagnosis. Panel B: Volume status assessment illustration showing three patient archetypes: hypovolemic (dry mucous membranes, decreased skin turgor, tachycardia), euvolemic (normal examination), and hypervolemic (peripheral edema, ascites, jugular venous distension), with underlying mechanisms labeled. Panel C: Urine studies interpretation diagram showing urine sodium below 20 (sodium retention, low effective circulating volume) versus above 40 (renal wasting or SIADH), and urine osmolality below 100 (primary polydipsia, dilute urine) versus above 100 (ADH present), with diagnostic significance annotations. Panel D: SIADH diagnostic criteria checklist showing six required elements (low serum sodium, low serum osmolality, concentrated urine, elevated urine sodium, euvolemia, exclusion of hypothyroidism and adrenal insufficiency) alongside common causes organized by category (CNS, pulmonary, medications, postoperative).</image>

Section 3: Hyponatremia Treatment

The treatment of acute symptomatic hyponatremia is a medical emergency that requires prompt intervention to prevent life-threatening neurological complications. Three-percent hypertonic saline is the treatment of choice, administered as a one hundred to one hundred fifty milliliter bolus over ten to twenty minutes. The initial goal is to raise the serum sodium by four to six milliequivalents per liter within the first few hours, which is typically sufficient to reduce cerebral edema and resolve seizures, obtundation, and other acute neurological symptoms. The bolus may be repeated one to two additional times if symptoms do not improve, with sodium levels checked after each bolus. This treatment should be administered in an intensive care unit setting with frequent neurological assessments and serial sodium measurements every one to two hours during the acute correction phase.

The treatment of chronic hyponatremia is guided by the underlying etiology and volume status. For hypovolemic hyponatremia, the primary treatment is volume repletion with isotonic normal saline, which restores intravascular volume, suppresses ADH release, and allows the kidneys to excrete the excess free water, thereby correcting the sodium concentration. For euvolemic hyponatremia from SIADH, the cornerstone of treatment is fluid restriction to one to 1.5 liters per day, supplemented by salt tablets to increase solute intake and enhance free water excretion; urea may be used as an alternative osmotic agent. For hypervolemic hyponatremia from heart failure, cirrhosis, or nephrotic syndrome, fluid restriction combined with loop diuretics to promote free water excretion is the primary approach, with treatment of the underlying condition being essential for long-term management. Vasopressin receptor antagonists, such as tolvaptan, may be considered in refractory cases of euvolemic or hypervolemic hyponatremia but require careful monitoring due to the risk of overly rapid correction.

The rate of sodium correction in chronic hyponatremia is critically important and must be carefully controlled to prevent osmotic demyelination syndrome. The maximum safe correction rate for chronic hyponatremia is eight to ten milliequivalents per liter in any twenty-four-hour period, with a more conservative limit of six to eight milliequivalents per liter recommended for patients at high risk for osmotic demyelination. Sodium levels should be monitored every four to six hours during the initial correction phase to ensure that the rate does not exceed the safe threshold. High-risk populations for osmotic demyelination include patients with severe hyponatremia (sodium below one hundred twenty), chronic alcoholism, malnutrition, hypokalemia, and liver disease, who may be particularly vulnerable to the demyelinating process even with correction rates considered safe for the general population.

Osmotic demyelination syndrome, formerly known as central pontine myelinolysis, is the most feared complication of overly rapid sodium correction and can produce devastating and irreversible neurological injury. The pathophysiology involves osmotic stress to oligodendrocytes in the central pons and extrapontine regions, leading to demyelination that manifests days after the overcorrection event. Clinical features include a delayed onset of neurological deterioration occurring two to six days after correction, with symptoms including dysarthria, dysphagia, quadriparesis, locked-in syndrome, and altered consciousness. If overcorrection is recognized, immediate therapeutic measures should be instituted to re-lower the sodium, including administration of five-percent dextrose in water and desmopressin (DDAVP), which acts on vasopressin receptors in the collecting duct to promote water reabsorption and lower the sodium concentration. Prevention through meticulous monitoring and adherence to safe correction rates remains the most effective strategy against this devastating complication.

<image>Panel A: Emergency treatment protocol for acute symptomatic hyponatremia showing 3% hypertonic saline bolus (100-150 mL over 10-20 minutes), initial goal of raising sodium by 4-6 mEq/L, ICU setting with neurological monitoring, and repeat bolus option if symptoms persist, with serial sodium check timeline. Panel B: Chronic hyponatremia treatment by volume status showing three pathways: hypovolemic (normal saline repletion restoring volume and suppressing ADH), euvolemic SIADH (fluid restriction, salt tablets, urea), and hypervolemic (fluid restriction, loop diuretics, treat underlying condition), with expected sodium response curves. Panel C: Correction rate monitoring diagram showing safe limits of 8-10 mEq/L per 24 hours (general) and 6-8 mEq/L per 24 hours (high risk), with 4-6 hour sodium check intervals, and a graph plotting sodium level over time with safe correction zone highlighted in green and danger zone in red. Panel D: Osmotic demyelination syndrome illustration showing the central pons on MRI with characteristic demyelination, clinical timeline (overcorrection on day 0, symptom onset days 2-6), risk factors (chronic hyponatremia, alcoholism, malnutrition, hypokalemia), symptoms (dysarthria, dysphagia, quadriparesis), and rescue therapy (D5W plus desmopressin to re-lower sodium).</image>

Section 4: Hypernatremia

Hypernatremia, defined as a serum sodium concentration above one hundred forty-five milliequivalents per liter, fundamentally represents a deficit of total body water relative to total body sodium. The causes of hypernatremia are categorized by mechanism into three groups. Water loss is the most common mechanism and includes insensible losses through the skin and respiratory tract, gastrointestinal losses from diarrhea, and renal water losses from diabetes insipidus or osmotic diuresis. Inadequate water intake is a common contributing factor, particularly in patients with impaired thirst sensation (elderly, neurologically impaired) or decreased access to water (intubated, immobilized, or institutionalized patients). Sodium gain from administration of hypertonic saline, sodium bicarbonate, or excessive sodium-containing medications is a less common but iatrogenic cause. The most common clinical scenario for hypernatremia is an elderly, debilitated patient with impaired thirst who cannot access water independently.

Diabetes insipidus is an important cause of hypernatremia characterized by the production of large volumes of dilute urine due to deficient action of antidiuretic hormone. Central diabetes insipidus results from inadequate ADH production by the hypothalamus or secretion by the posterior pituitary and may be caused by pituitary surgery, traumatic brain injury, tumors, infiltrative diseases, and idiopathic autoimmune destruction. Nephrogenic diabetes insipidus results from resistance of the renal collecting duct to the action of ADH and may be caused by lithium therapy (the most common acquired cause), hypercalcemia, hypokalemia, chronic kidney disease, and medications including demeclocycline and foscarnet. Central and nephrogenic diabetes insipidus are distinguished by the water deprivation test followed by desmopressin administration: in central disease, desmopressin administration concentrates the urine, while in nephrogenic disease, the urine remains dilute because the kidneys cannot respond to exogenous vasopressin.

The clinical manifestations of hypernatremia are primarily neurological and result from cellular dehydration as water moves osmotically from the intracellular to the extracellular compartment. Mild hypernatremia produces thirst, weakness, and irritability. Moderate hypernatremia causes confusion, lethargy, and muscle twitching. Severe hypernatremia can cause seizures, coma, and, uniquely, intracranial hemorrhage resulting from shrinkage of brain parenchyma away from the meninges with rupture of bridging veins. As with hyponatremia, the rate of development determines the severity of symptoms: acute hypernatremia is more symptomatic because the brain has not had time to adapt, while chronic hypernatremia allows the brain to accumulate intracellular osmolytes (idiogenic osmoles) that reduce cellular shrinkage and attenuate symptoms. This cerebral adaptation, while protective in the chronic state, makes overly rapid correction of chronic hypernatremia dangerous because the now-osmolyte-enriched brain cells may swell excessively when exposed to a rapidly normalizing extracellular fluid, causing cerebral edema.

The treatment of hypernatremia centers on free water replacement to correct the water deficit while addressing the underlying cause. The free water deficit is estimated using the formula: total body water multiplied by the quantity of (current sodium divided by one hundred forty, minus one), where total body water is estimated as sixty percent of body weight in kilograms for men and fifty percent for women. Free water can be replaced using hypotonic fluids including five-percent dextrose in water, which distributes as pure free water once the dextrose is metabolized, or half-normal saline. The correction rate should not exceed ten to twelve milliequivalents per liter in any twenty-four-hour period to avoid cerebral edema from overly rapid correction. Central diabetes insipidus is treated with desmopressin, a synthetic vasopressin analog that acts on V2 receptors in the collecting duct to promote water reabsorption. Nephrogenic diabetes insipidus is more challenging to treat and may respond to thiazide diuretics, which paradoxically reduce urine volume by promoting proximal sodium and water reabsorption, combined with a low-sodium diet to reduce solute load and urine output.

<image>Panel A: Hypernatremia pathophysiology diagram showing three mechanisms converging on elevated serum sodium: water loss (insensible, GI, renal), inadequate intake (impaired thirst, decreased access), and sodium gain (hypertonic saline, sodium bicarbonate), with the elderly debilitated patient as the most common clinical scenario. Panel B: Diabetes insipidus comparison showing central DI (pituitary pathology, inadequate ADH production, responds to desmopressin) versus nephrogenic DI (renal resistance to ADH, lithium as most common acquired cause, does not respond to desmopressin), with water deprivation test results illustrated. Panel C: Clinical manifestation spectrum of hypernatremia from mild (thirst, weakness) through moderate (confusion, lethargy) to severe (seizures, coma, intracranial hemorrhage from brain shrinkage with bridging vein rupture), with brain cross-sections showing progressive cellular dehydration. Panel D: Treatment algorithm showing free water deficit formula (TBW x [Na/140 - 1]), fluid options (D5W as pure free water, half-normal saline), safe correction rate (10-12 mEq/L per 24 hours), central DI treatment (desmopressin), and nephrogenic DI treatment (thiazide diuretics, low-sodium diet).</image>

Section 5: Potassium Disorders

Potassium is the major intracellular cation, with approximately ninety-eight percent of total body potassium located within cells and only two percent in the extracellular fluid. The normal serum potassium concentration ranges from 3.5 to 5.0 milliequivalents per liter, and even small changes in extracellular potassium have profound effects on cellular membrane potential and excitability, particularly in cardiac and skeletal muscle. Potassium homeostasis is regulated by both external balance (renal excretion, primarily under the influence of aldosterone) and internal balance (transcellular shifts between the intracellular and extracellular compartments). Transcellular shifts are mediated by several factors: insulin promotes potassium uptake into cells via the sodium-potassium ATPase, catecholamines and beta-2 adrenergic agonists similarly promote cellular potassium uptake, and acid-base status affects potassium distribution, with acidosis causing potassium to shift out of cells (raising serum potassium) and alkalosis causing potassium to shift into cells (lowering serum potassium).

Hypokalemia, defined as a serum potassium below 3.5 milliequivalents per liter, has multiple etiologies that are categorized by mechanism. Gastrointestinal losses, particularly diarrhea and vomiting, are among the most common causes; notably, the hypokalemia in vomiting is primarily due to renal potassium wasting from metabolic alkalosis and volume depletion rather than direct gastrointestinal potassium loss. Renal losses from diuretic therapy (particularly loop and thiazide diuretics), hyperaldosteronism, and other mineralocorticoid excess states are major causes of chronic hypokalemia. Transcellular shifts from insulin administration, beta-2 agonist therapy, and alkalosis can produce acute hypokalemia without a true total body potassium deficit. Decreased dietary intake alone rarely causes clinically significant hypokalemia unless combined with other losses, as the kidneys can reduce potassium excretion to very low levels in the setting of potassium depletion.

The clinical manifestations of hypokalemia reflect the dependence of cardiac and skeletal muscle function on normal potassium-mediated membrane potential. Cardiac manifestations include characteristic electrocardiographic changes: flattened T waves, the appearance of U waves (a positive deflection following the T wave), ST-segment depression, prolonged QT interval, and, in severe cases, ventricular arrhythmias including torsades de pointes and ventricular fibrillation. Muscular manifestations range from mild weakness and muscle cramps to severe generalized weakness and, in extreme cases, ascending paralysis and respiratory failure. Gastrointestinal effects include decreased intestinal motility progressing to frank ileus. Renal effects include impaired concentrating ability, producing a state of nephrogenic diabetes insipidus with polyuria and polydipsia. These manifestations tend to worsen progressively with decreasing potassium levels, although the rate of decline is also important, as acute hypokalemia is more likely to produce symptoms than chronic hypokalemia at the same absolute level.

Treatment of hypokalemia is guided by severity and the route of replacement. Mild hypokalemia with a potassium level of 3.0 to 3.5 milliequivalents per liter can typically be managed with oral potassium chloride supplementation at a dose of forty to eighty milliequivalents per day. Moderate hypokalemia with a potassium level of 2.5 to 3.0 milliequivalents per liter may require oral or intravenous replacement depending on symptoms and the clinical setting. Severe hypokalemia below 2.5 milliequivalents per liter or hypokalemia with ECG changes or symptoms warrants intravenous potassium chloride with continuous cardiac monitoring. The maximum safe rate of peripheral intravenous potassium administration is ten to twenty milliequivalents per hour through a peripheral vein, with higher rates requiring central venous access and intensive monitoring. A critical principle is that concurrent hypomagnesemia must be identified and corrected, as magnesium depletion renders hypokalemia refractory to potassium replacement by allowing ongoing renal potassium wasting through uninhibited ROMK channels in the distal nephron.

<image>Panel A: Potassium physiology diagram showing 98% intracellular and 2% extracellular distribution, normal serum range 3.5-5.0 mEq/L, with regulatory mechanisms: aldosterone (renal excretion), insulin and beta-2 agonists (cellular uptake via Na-K ATPase), and acid-base effects (acidosis shifts potassium out, alkalosis shifts potassium in). Panel B: Hypokalemia causes organized by mechanism: GI losses (diarrhea, vomiting with secondary renal wasting), renal losses (diuretics, hyperaldosteronism), transcellular shifts (insulin, beta-agonists, alkalosis), and decreased intake (rare as sole cause), with relative frequency annotations. Panel C: ECG progression in hypokalemia showing normal tracing, then progressive changes: flattened T waves, prominent U waves, ST depression, prolonged QT interval, and severe ventricular arrhythmia, alongside clinical manifestations (weakness, cramping, ileus, nephrogenic DI). Panel D: Treatment ladder for hypokalemia showing mild (oral KCl 40-80 mEq/day), moderate (oral or IV KCl), severe (IV KCl with cardiac monitoring, max 10-20 mEq/hr peripherally), with prominent "Check and replace magnesium" callout emphasizing the importance of correcting concurrent hypomagnesemia.</image>

Section 6: Hyperkalemia

Hyperkalemia, defined as a serum potassium above 5.0 milliequivalents per liter, is a potentially life-threatening electrolyte emergency that requires prompt recognition and management. The causes of hyperkalemia are organized by mechanism. Decreased renal excretion is the most common cause and includes acute kidney injury, chronic kidney disease, hypoaldosteronism (type four renal tubular acidosis), and medications that impair renal potassium excretion such as angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, potassium-sparing diuretics (spironolactone, eplerenone, amiloride, triamterene), nonsteroidal anti-inflammatory drugs, and trimethoprim. Transcellular shifts from the intracellular to the extracellular compartment occur in metabolic acidosis, insulin deficiency (diabetic ketoacidosis), beta-blocker therapy, digoxin toxicity, and cell lysis states including rhabdomyolysis, tumor lysis syndrome, and massive hemolysis. Increased potassium intake from intravenous potassium administration, oral supplements, or massive blood transfusion may contribute, particularly in patients with impaired renal excretion. Pseudohyperkalemia, a falsely elevated potassium level caused by hemolysis of the blood sample during collection, thrombocytosis, or severe leukocytosis, must be excluded before initiating treatment.

The electrocardiographic changes of hyperkalemia progress in a characteristic and predictable pattern that correlates with potassium levels, although individual variability exists. At potassium levels of 5.5 to 6.5 milliequivalents per liter, peaked, narrow, symmetric T waves appear, reflecting accelerated repolarization. As potassium rises to 6.5 to 7.5 milliequivalents per liter, the PR interval prolongs and the QRS complex widens, reflecting slowed conduction through the atria and ventricles. At levels of 7.5 to 8.0 milliequivalents per liter, the P wave disappears as atrial activity ceases, and the widened QRS may merge with the T wave to produce a sinusoidal wave pattern. At levels above 8.0 milliequivalents per liter, cardiac arrest may occur from ventricular fibrillation or asystole. It is essential to recognize that these correlations are approximate, and life-threatening arrhythmias can occur at lower potassium levels, particularly in patients with underlying heart disease or concurrent electrolyte abnormalities. Any patient with hyperkalemia and ECG changes requires immediate emergency treatment regardless of the absolute potassium level.

The treatment of hyperkalemia follows a hierarchical approach organized by mechanism of action and urgency. Calcium gluconate is the first agent administered in emergency hyperkalemia with ECG changes, as it stabilizes the cardiac cell membrane potential within minutes, reducing the risk of fatal arrhythmia, although it does not lower the serum potassium level. The second tier involves agents that shift potassium from the extracellular to the intracellular compartment: regular insulin (ten units intravenously with twenty-five grams of dextrose to prevent hypoglycemia) lowers potassium by 0.5 to 1.2 milliequivalents per liter within fifteen to thirty minutes, and nebulized beta-2 agonists (albuterol ten to twenty milligrams) provide an additive shift effect. Sodium bicarbonate may provide modest benefit in acidotic patients but is not effective as monotherapy and should not be relied upon as a primary treatment. The third tier involves agents that eliminate potassium from the body: loop diuretics promote renal potassium excretion, sodium polystyrene sulfonate (Kayexalate) and the newer agent patiromer bind potassium in the gastrointestinal tract for fecal excretion, and hemodialysis provides the most rapid and effective removal of potassium from the body and is indicated for severe or refractory hyperkalemia, particularly in patients with renal failure.

The management algorithm for hyperkalemia integrates the severity of hyperkalemia, the presence of ECG changes, and the clinical context. Mild hyperkalemia (5.5 to 6.0 milliequivalents per liter) without ECG changes may be managed by removing the inciting cause, restricting dietary potassium, and discontinuing offending medications. Moderate hyperkalemia (6.0 to 6.5 milliequivalents per liter) warrants the above measures plus initiation of potassium-lowering agents such as diuretics, and consideration of insulin with glucose if the potassium is trending upward. Severe hyperkalemia above 6.5 milliequivalents per liter or any level with ECG changes constitutes a medical emergency requiring immediate calcium gluconate for cardiac membrane stabilization, insulin with glucose and beta-2 agonists for rapid transcellular shift, and definitive potassium removal with loop diuretics and/or hemodialysis. Continuous cardiac monitoring is essential throughout the treatment of moderate to severe hyperkalemia, and serum potassium should be rechecked every one to two hours until the level stabilizes within the safe range.

<image>Panel A: Hyperkalemia causes organized by mechanism: decreased renal excretion (AKI, CKD, hypoaldosteronism, ACEi/ARBs, K-sparing diuretics, NSAIDs), transcellular shift out of cells (acidosis, insulin deficiency, beta-blockers, cell lysis), increased intake (IV potassium, supplements, transfusions), and pseudohyperkalemia (hemolyzed sample, thrombocytosis). Panel B: ECG progression of hyperkalemia showing four sequential tracings: peaked T waves at K 5.5-6.5, prolonged PR and widened QRS at K 6.5-7.5, absent P waves and sine wave pattern at K 7.5-8.0, and ventricular fibrillation or asystole at K above 8.0, with potassium level annotations. Panel C: Treatment hierarchy pyramid showing three tiers: Tier 1 membrane stabilization (calcium gluconate, immediate onset, 30-60 min duration), Tier 2 transcellular shift (insulin plus glucose and beta-2 agonists, 15-30 min onset, 4-6 hr duration), and Tier 3 potassium elimination (loop diuretics, Kayexalate, hemodialysis, varying onset and duration). Panel D: Management algorithm flowchart branching by severity: mild (remove cause, restrict potassium, stop offending drugs), moderate (above plus diuretics, consider insulin/glucose), and severe or ECG changes (calcium gluconate immediately, insulin/glucose, beta-agonists, loop diuretics, consider hemodialysis), with continuous cardiac monitoring emphasized.</image>

Section 7: Calcium Disorders

Calcium physiology is complex, involving three distinct fractions in the blood and multiple hormonal regulatory systems. The normal total serum calcium ranges from 8.5 to 10.5 milligrams per deciliter, while ionized calcium, which represents the physiologically active fraction, ranges from 4.5 to 5.5 milligrams per deciliter. Approximately forty percent of total serum calcium is bound to albumin, forty percent is in the ionized (free) form, and the remaining twenty percent is complexed with anions such as phosphate and citrate. Because the total calcium level is affected by albumin binding, a corrected calcium should be calculated in patients with hypoalbuminemia by adding 0.8 milligrams per deciliter of calcium for each one gram per deciliter decrease in albumin below four. Calcium homeostasis is regulated primarily by parathyroid hormone, which raises serum calcium by promoting bone resorption, increasing renal calcium reabsorption, and stimulating renal production of active vitamin D (calcitriol), and by vitamin D, which promotes intestinal calcium absorption. Calcitonin, secreted by thyroid parafollicular C-cells, has a modest calcium-lowering effect but is of limited physiologic significance.

Hypercalcemia, defined as total calcium above 10.5 milligrams per deciliter or ionized calcium above 5.5 milligrams per deciliter, has two causes that account for approximately ninety percent of cases: primary hyperparathyroidism and malignancy. Primary hyperparathyroidism is the most common cause of hypercalcemia in the outpatient setting and is typically caused by a solitary parathyroid adenoma that produces excess parathyroid hormone, leading to chronic, usually mild hypercalcemia with elevated or inappropriately normal PTH levels. Malignancy-associated hypercalcemia is the most common cause in hospitalized patients and may be mediated by PTH-related peptide secretion (humoral hypercalcemia of malignancy), direct osteolytic bone metastases, or tumor production of calcitriol (as in lymphoma). Other causes include vitamin D intoxication, granulomatous diseases (sarcoidosis, tuberculosis) producing calcitriol, thiazide diuretics reducing renal calcium excretion, prolonged immobilization promoting bone resorption, and hyperthyroidism increasing bone turnover. The classic mnemonic for hypercalcemia symptoms is "stones, bones, groans, moans, and psychiatric overtones," referring to kidney stones, bone pain, abdominal pain (groans), muscle weakness and fatigue (moans), and confusion and depression.

The treatment of hypercalcemia is determined by severity and symptoms. Mild hypercalcemia (calcium below twelve milligrams per deciliter) in an asymptomatic patient can be managed with adequate hydration, treatment of the underlying cause, and monitoring. Moderate hypercalcemia (twelve to fourteen milligrams per deciliter) requires intravenous normal saline at aggressive rates (two hundred to three hundred milliliters per hour initially) to restore volume and promote renal calcium excretion, and loop diuretics may be added after volume repletion to further enhance calciuresis. Severe hypercalcemia (above fourteen milligrams per deciliter) is a medical emergency requiring aggressive intravenous saline hydration, calcitonin for rapid but transient calcium lowering (onset within hours), and bisphosphonates such as zoledronic acid or pamidronate for sustained calcium reduction (onset within two to four days). In life-threatening or refractory cases, hemodialysis with a low-calcium or calcium-free dialysate provides the most rapid definitive calcium reduction.

Hypocalcemia, defined as total calcium below 8.5 milligrams per deciliter (corrected for albumin) or ionized calcium below 4.5 milligrams per deciliter, has several important causes. Hypoparathyroidism, most commonly resulting from inadvertent parathyroid removal or damage during thyroid or parathyroid surgery, is a major cause. Vitamin D deficiency from inadequate dietary intake, malabsorption, or chronic kidney disease with impaired calcitriol production is another common etiology. Hypomagnesemia causes hypocalcemia through impaired PTH secretion and PTH resistance, and the hypocalcemia will be refractory to treatment until magnesium is repleted. Other causes include acute pancreatitis (calcium saponification), sepsis, massive blood transfusion with citrate binding, and medications such as bisphosphonates and denosumab. The clinical manifestations of hypocalcemia include neuromuscular excitability manifesting as perioral and extremity paresthesias, muscle cramps, tetany, and seizures. Two classic bedside signs are the Chvostek sign (twitching of facial muscles upon tapping the facial nerve anterior to the ear) and the Trousseau sign (carpal spasm induced by inflating a blood pressure cuff above systolic pressure for three minutes). Severe symptomatic hypocalcemia is treated with intravenous calcium gluconate, while chronic hypocalcemia is managed with oral calcium and vitamin D supplementation.

<image>Panel A: Calcium physiology diagram showing three calcium fractions in blood (40% albumin-bound, 40% ionized/active, 20% complexed), albumin correction formula, and regulatory hormones: PTH (from parathyroid glands, raises calcium via bone resorption, renal reabsorption, and vitamin D activation) and vitamin D (promotes intestinal calcium absorption). Panel B: Hypercalcemia differential diagnosis showing two major causes (primary hyperparathyroidism with parathyroid adenoma, and malignancy with PTHrP, osteolytic metastases, and calcitriol production) alongside minor causes (vitamin D excess, granulomatous disease, thiazides, immobilization), with the "stones, bones, groans, moans, psychiatric overtones" mnemonic illustrated. Panel C: Hypercalcemia treatment ladder showing mild (hydration, treat cause), moderate (IV normal saline, loop diuretics after repletion), and severe (aggressive IV saline, calcitonin for rapid onset, bisphosphonates for sustained reduction, hemodialysis if refractory), with onset times annotated for each intervention. Panel D: Hypocalcemia panel showing causes (hypoparathyroidism, vitamin D deficiency, hypomagnesemia, pancreatitis), clinical features (paresthesias, tetany, seizures), bedside signs (Chvostek sign with facial nerve tapping, Trousseau sign with BP cuff inflation and carpal spasm), and treatment (IV calcium gluconate for severe, oral calcium and vitamin D for chronic).</image>

Section 8: Magnesium Disorders

Magnesium is the fourth most abundant cation in the body and the second most abundant intracellular cation, playing a critical role in numerous enzymatic reactions, neuromuscular function, and cardiac electrophysiology. The normal serum magnesium ranges from 1.7 to 2.5 milligrams per deciliter, although serum levels may not accurately reflect total body stores because only one percent of total body magnesium is in the extracellular fluid, with approximately fifty percent stored in bone and the remainder in the intracellular compartment. Magnesium serves as a cofactor for over three hundred enzymatic reactions, including those involved in ATP production, DNA and protein synthesis, and neuromuscular transmission. The kidney is the primary regulator of magnesium homeostasis, with the thick ascending limb of the loop of Henle being the major site of magnesium reabsorption. Magnesium depletion is common in hospitalized patients and is frequently underdiagnosed because serum levels may remain within the normal range despite significant total body depletion.

Hypomagnesemia, defined as a serum magnesium below 1.7 milligrams per deciliter, has multiple causes organized by mechanism. Gastrointestinal losses from chronic diarrhea, malabsorption syndromes, and chronic proton pump inhibitor use are common causes; PPI-associated hypomagnesemia is an increasingly recognized entity that can be severe and refractory, and it is thought to result from impaired intestinal magnesium absorption through transient receptor potential melastatin channels. Renal losses occur with diuretic therapy (both loop and thiazide diuretics increase urinary magnesium excretion), chronic alcoholism (ethanol directly impairs renal tubular magnesium reabsorption), and medications including aminoglycosides, amphotericin B, cisplatin, and calcineurin inhibitors. Decreased dietary intake from malnutrition contributes to magnesium depletion, particularly in alcoholic patients. Other causes include hungry bone syndrome following parathyroidectomy, acute pancreatitis, and refeeding syndrome.

The clinical manifestations of hypomagnesemia are primarily cardiac and neuromuscular and have critical overlap with hypocalcemia and hypokalemia. Cardiac manifestations include atrial and ventricular arrhythmias, QT prolongation, and torsades de pointes, a polymorphic ventricular tachycardia that can degenerate into ventricular fibrillation. Neuromuscular manifestations include tremor, hyperreflexia, muscle fasciculations, tetany, and seizures. Perhaps the most clinically important consequence of hypomagnesemia is its ability to cause refractory hypokalemia and refractory hypocalcemia. Magnesium depletion causes refractory hypokalemia by activating ROMK potassium channels in the distal nephron, promoting ongoing renal potassium wasting that cannot be corrected by potassium supplementation alone until magnesium stores are repleted. Hypomagnesemia causes hypocalcemia through impaired parathyroid hormone secretion and peripheral resistance to PTH action, and this hypocalcemia will also be refractory to calcium and vitamin D supplementation until magnesium is corrected.

Treatment of hypomagnesemia depends on severity and the clinical context. Mild asymptomatic hypomagnesemia can be treated with oral magnesium oxide or magnesium gluconate, although oral magnesium preparations have limited bioavailability and may cause diarrhea, which paradoxically worsens magnesium losses. Moderate to severe hypomagnesemia requires intravenous magnesium sulfate, typically administered as one to two grams (eight to sixteen milliequivalents) over one to two hours, followed by additional doses as needed to achieve a serum level within the normal range. In the life-threatening setting of torsades de pointes, intravenous magnesium sulfate two grams is administered as a rapid bolus over one to two minutes regardless of the serum magnesium level, as magnesium acts as a membrane stabilizer that suppresses the triggered activity and early afterdepolarizations responsible for this arrhythmia. In patients with renal failure, magnesium replacement must be administered cautiously with reduced doses and close monitoring, as impaired renal excretion predisposes to hypermagnesemia. Addressing the underlying cause of magnesium depletion is essential for sustained correction.

<image>Panel A: Magnesium physiology diagram showing total body distribution (50% bone, 49% intracellular, 1% extracellular), normal serum range 1.7-2.5 mg/dL, major functions (enzyme cofactor for 300+ reactions, ATP production, neuromuscular transmission), and renal regulation at the thick ascending limb of the loop of Henle. Panel B: Hypomagnesemia causes showing GI losses (diarrhea, malabsorption, PPIs with mechanism at TRPM channels), renal losses (diuretics, alcoholism, aminoglycosides, cisplatin), decreased intake (malnutrition), and other causes (hungry bone syndrome, pancreatitis, refeeding), with relative frequency annotations. Panel C: Clinical manifestations diagram showing cardiac effects (arrhythmias, QT prolongation, torsades de pointes ECG tracing), neuromuscular effects (tremor, hyperreflexia, tetany, seizures), and the critical concept of refractory hypokalemia (ROMK channel activation causing ongoing renal K wasting) and refractory hypocalcemia (impaired PTH secretion and resistance). Panel D: Treatment algorithm showing mild (oral magnesium oxide or gluconate), moderate-severe (IV magnesium sulfate 1-2 g over 1-2 hours), torsades de pointes emergency (IV magnesium 2 g bolus over 1-2 minutes), and renal failure caution (reduced dose, close monitoring), with note to address underlying cause.</image>

Section 9: Phosphorus Disorders

Phosphorus is an essential mineral with approximately eighty-five percent of total body stores located in bone and the remainder distributed in soft tissues and the extracellular fluid. The normal serum phosphorus ranges from 2.5 to 4.5 milligrams per deciliter, and phosphorus plays critical roles in energy metabolism as a component of adenosine triphosphate, in bone mineralization as a component of hydroxyapatite, in nucleic acid structure, in cell membrane composition as phospholipids, and in acid-base buffering. Phosphorus homeostasis is regulated by parathyroid hormone (which promotes renal phosphorus excretion), active vitamin D or calcitriol (which promotes intestinal phosphorus absorption), and fibroblast growth factor-23 (which is produced by osteocytes and promotes renal phosphorus excretion). The kidney is the primary organ of phosphorus regulation, with the proximal tubule being the major site of phosphorus reabsorption through sodium-phosphate cotransporters.

Hypophosphatemia, defined as a serum phosphorus below 2.5 milligrams per deciliter, occurs through three primary mechanisms. Transcellular shift of phosphorus from the extracellular to the intracellular compartment is an important and often acute mechanism, occurring during refeeding syndrome (as insulin drives phosphorus into cells along with glucose), insulin administration in diabetic ketoacidosis treatment, and respiratory alkalosis (which stimulates intracellular glycolysis and phosphorus consumption). Decreased intestinal absorption occurs with vitamin D deficiency, chronic antacid use (aluminum and magnesium hydroxide bind phosphorus in the GI tract), and malabsorption syndromes. Increased renal losses result from hyperparathyroidism, renal tubular defects, and osmotic diuresis. Refeeding syndrome deserves special emphasis: when severely malnourished patients receive carbohydrate nutrition, the resulting insulin surge drives phosphorus, potassium, and magnesium into cells, potentially causing life-threatening hypophosphatemia, cardiac arrhythmias, respiratory failure from diaphragm weakness, and death if not anticipated and managed prophylactically.

The clinical manifestations of hypophosphatemia correlate with severity. Mild hypophosphatemia is usually asymptomatic. Severe hypophosphatemia, with a serum level below 1.0 milligram per deciliter, can cause profound and dangerous complications. Skeletal muscle weakness may affect respiratory muscles, leading to respiratory failure and difficulty weaning from mechanical ventilation. Rhabdomyolysis can occur due to cellular energy depletion in skeletal muscle. Hemolytic anemia results from decreased erythrocyte ATP content, causing membrane instability and red cell lysis. Very severe hypophosphatemia can cause cardiac dysfunction with reduced myocardial contractility, impaired leukocyte function with increased infection susceptibility, and neurological manifestations including irritability, confusion, seizures, and coma. The broad range of clinical effects reflects the fundamental importance of phosphorus in cellular energy metabolism.

Hyperphosphatemia, defined as a serum phosphorus above 4.5 milligrams per deciliter, is most commonly caused by decreased renal excretion in chronic kidney disease, which is by far the most prevalent etiology. Other causes include increased phosphorus intake from excessive oral or intravenous phosphorus, phosphate-containing enemas, and excessive cow's milk consumption in infants. Cellular lysis from tumor lysis syndrome, rhabdomyolysis, and massive hemolysis releases large quantities of intracellular phosphorus into the extracellular fluid. Hypoparathyroidism reduces renal phosphorus excretion, and vitamin D intoxication increases intestinal absorption. The primary clinical consequence of hyperphosphatemia is the formation of calcium-phosphate complexes that deposit in soft tissues (metastatic calcification) when the calcium-phosphorus product exceeds fifty-five to seventy, and chronic hyperphosphatemia in kidney disease is associated with vascular calcification and increased cardiovascular mortality. Acute severe hyperphosphatemia can cause acute hypocalcemia as calcium complexes with the excess phosphorus. Treatment of hyperphosphatemia includes dietary phosphorus restriction, phosphate binders (calcium acetate, sevelamer, lanthanum) taken with meals to reduce intestinal absorption, and dialysis for severe or refractory cases.

<image>Panel A: Phosphorus physiology diagram showing total body distribution (85% bone, remaining in soft tissues and ECF), normal serum range 2.5-4.5 mg/dL, key functions (ATP energy metabolism, bone hydroxyapatite, nucleic acid structure, cell membrane phospholipids), and regulatory hormones (PTH promotes renal excretion, vitamin D promotes intestinal absorption, FGF-23 promotes renal excretion). Panel B: Hypophosphatemia mechanisms showing transcellular shift (refeeding syndrome with insulin driving phosphorus into cells, DKA treatment, respiratory alkalosis), decreased absorption (vitamin D deficiency, antacids, malabsorption), and increased renal losses (hyperparathyroidism, tubular defects), with refeeding syndrome danger alert highlighting cardiac and respiratory risks. Panel C: Hypophosphatemia clinical manifestations arranged by organ system: skeletal muscle (weakness, respiratory failure, rhabdomyolysis), hematologic (hemolytic anemia from RBC ATP depletion), cardiac (reduced contractility), immune (impaired leukocyte function), and neurologic (confusion, seizures), all linked to cellular energy depletion. Panel D: Hyperphosphatemia panel showing causes (CKD as most common, cellular lysis from tumor lysis/rhabdomyolysis, excessive intake, hypoparathyroidism), consequences (calcium-phosphate precipitation, metastatic calcification in blood vessels, acute hypocalcemia), and treatment (dietary restriction, phosphate binders with meals, dialysis for severe cases).</image>

Section 10: Clinical Pearls

Electrolyte emergencies require immediate recognition and treatment to prevent cardiac arrest and neurological catastrophe. Severe hyperkalemia with ECG changes is the most dangerous electrolyte emergency and requires immediate administration of calcium gluconate for membrane stabilization, followed by insulin with glucose and beta-2 agonists for transcellular shift, and definitive potassium removal by loop diuretics or hemodialysis. Symptomatic severe hyponatremia with seizures or altered mental status requires emergent three-percent hypertonic saline to raise the sodium by four to six milliequivalents per liter within the first hours. Severe hypocalcemia presenting with tetany or seizures necessitates immediate intravenous calcium gluconate. Torsades de pointes from hypomagnesemia or QT prolongation requires immediate intravenous magnesium sulfate two grams as a bolus, regardless of the measured serum magnesium level.

Recognizing common electrolyte patterns and associations allows clinicians to anticipate and prevent secondary electrolyte disturbances. Hypokalemia and hypomagnesemia commonly coexist because they share etiologies (diuretic use, alcoholism) and because magnesium depletion causes renal potassium wasting. Hypokalemia and metabolic alkalosis are frequently paired because vomiting and diuretics simultaneously cause both, and each condition perpetuates the other through reciprocal renal mechanisms. Hypocalcemia and hypomagnesemia coexist in alcoholism, malnutrition, and refeeding syndrome, and hypomagnesemia must be corrected before hypocalcemia will respond to treatment. Hyperkalemia and metabolic acidosis occur together in type four renal tubular acidosis, chronic kidney disease, and adrenal insufficiency, where aldosterone deficiency or resistance simultaneously impairs both potassium excretion and hydrogen ion secretion.

Medications are among the most common causes of electrolyte disturbances in hospitalized patients, and awareness of drug-electrolyte interactions is essential for prevention and management. Thiazide diuretics characteristically cause hypokalemia, hyponatremia, and hypercalcemia (by enhancing calcium reabsorption in the distal tubule). Loop diuretics cause hypokalemia, hyponatremia, hypocalcemia (opposite to thiazides), and hypomagnesemia by impairing the paracellular reabsorption of divalent cations in the thick ascending limb. Angiotensin-converting enzyme inhibitors and angiotensin receptor blockers cause hyperkalemia by reducing aldosterone-mediated renal potassium secretion. Lithium causes nephrogenic diabetes insipidus and consequent hypernatremia by inhibiting aquaporin-2 channel expression. Proton pump inhibitors cause hypomagnesemia through impaired intestinal magnesium absorption. Recognizing these patterns allows clinicians to monitor the appropriate electrolytes when initiating these medications and to consider the medication list when evaluating an unexplained electrolyte disturbance.

Monitoring frequency for electrolyte disorders must be matched to the severity and treatment urgency. Hyponatremia correction should be monitored with sodium levels every four to six hours during the active correction phase to ensure adherence to safe correction rates and prevent osmotic demyelination syndrome. Hyperkalemia treatment should be followed with repeat potassium levels every two hours until the level stabilizes within the safe range, along with continuous cardiac monitoring for arrhythmia detection. Severe hypocalcemia warrants continuous cardiac monitoring due to the risk of QT prolongation and ventricular arrhythmias. Severe hypomagnesemia should be monitored with magnesium levels every six hours until adequate repletion is confirmed. All electrolyte disorders should be rechecked daily during hospitalization, and more frequently during active repletion or correction, to ensure that the therapeutic response is appropriate and that overcorrection does not occur.

<image>Panel A: Electrolyte emergency response cards showing four critical scenarios with immediate treatments: hyperkalemia with ECG changes (calcium gluconate, insulin/glucose, dialysis), symptomatic hyponatremia (3% saline bolus), severe hypocalcemia with tetany (IV calcium gluconate), and torsades de pointes (IV magnesium 2g bolus), each with dosing and monitoring annotations. Panel B: Common electrolyte association patterns diagram showing four linked pairs: hypokalemia plus hypomagnesemia (diuretics, alcoholism), hypokalemia plus metabolic alkalosis (vomiting, diuretics), hypocalcemia plus hypomagnesemia (alcoholism, refeeding), and hyperkalemia plus metabolic acidosis (type 4 RTA, CKD), with bidirectional arrows showing mutual perpetuation. Panel C: Medication-electrolyte effects chart showing thiazides (decrease K and Na, increase Ca), loop diuretics (decrease K, Na, Ca, Mg), ACEi/ARBs (increase K), lithium (increase Na via nephrogenic DI), and PPIs (decrease Mg), with monitoring recommendations for each drug class. Panel D: Monitoring frequency guide showing hyponatremia correction (Na every 4-6 hours), hyperkalemia treatment (K every 2 hours plus continuous cardiac monitoring), severe hypocalcemia (continuous cardiac monitoring), and severe hypomagnesemia (Mg every 6 hours), displayed as a clinical timeline with check-point markers.</image>

Summary

• Hyponatremia is approached systematically: assess osmolality (hypotonic, isotonic, hypertonic), volume status (hypovolemic, euvolemic, hypervolemic), and urine studies (urine sodium, urine osmolality); SIADH is the most common cause of euvolemic hyponatremia
• Acute symptomatic hyponatremia requires 3% saline; chronic hyponatremia must be corrected no faster than 8-10 mEq/L per 24 hours to prevent osmotic demyelination syndrome
• Hypernatremia represents water deficit; treatment involves free water replacement with D5W or half-normal saline, correcting no faster than 10-12 mEq/L per 24 hours
• Hypokalemia is most commonly caused by GI and renal losses; always check and replace magnesium when treating refractory hypokalemia
• Hyperkalemia with ECG changes is a medical emergency: calcium gluconate for membrane stabilization, insulin/glucose for transcellular shift, and dialysis for definitive removal
• Hypercalcemia is most commonly caused by primary hyperparathyroidism (outpatient) or malignancy (inpatient); treat with IV saline hydration and bisphosphonates for severe cases
• Hypomagnesemia causes refractory hypokalemia and refractory hypocalcemia and must be corrected first
• Always correct magnesium when treating refractory potassium or calcium disorders
• ECG monitoring is essential for severe potassium and calcium disorders
• Avoid overcorrection of sodium disorders to prevent osmotic demyelination syndrome and cerebral edema

Key Terms

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