Electrolyte Disorders in ICU

Quick Answer

Electrolyte disorders are ubiquitous in critically ill patients, affecting up to 40-50% of ICU admissions and independently associated with increased mortality and length of stay. [1,2] The major ICU-relevant electrolyte emergencies include:

Hyponatremia: Severe hyponatremia (below 120 mmol/L) with neurological symptoms requires urgent treatment with 3% hypertonic saline (100 mL bolus raises Na+ ~2 mmol/L). Correction must be limited to below 8-10 mmol/L per 24 hours to prevent osmotic demyelination syndrome (ODS). [3,4]

Hypernatremia: Calculate free water deficit using the formula: TBW x [(Current Na/140) - 1]. Correct at below 10 mmol/L per 24 hours to prevent cerebral edema. [5]

Hypokalemia: ECG changes include U waves, ST depression, and T wave flattening. Replacement via IV KCl: 10 mmol/h peripheral, 20 mmol/h central line (maximum 40 mmol/h with cardiac monitoring). [6]

Hyperkalemia: Life-threatening when greater than 6.5 mmol/L with ECG changes (peaked T waves, widened QRS, sine wave pattern). Treatment sequence: calcium gluconate 10 mL 10% IV (membrane stabilization), insulin 10 units + dextrose 50 mL 50% (intracellular shift), salbutamol 10-20 mg nebulized, and dialysis for refractory cases. [7,8]

Calcium disorders: Ionized calcium (iCa2+) is the physiologically active fraction. Hypocalcemia (iCa2+ below 1.0 mmol/L) causes tetany, seizures, and prolonged QT; treat with calcium gluconate 10-20 mL 10% IV. Hypercalcemia (greater than 3.0 mmol/L) causes altered mental status and arrhythmias; treat with IV saline rehydration, loop diuretics, bisphosphonates, and calcitonin. [9,10]

Magnesium disorders: Hypomagnesemia (below 0.7 mmol/L) is the most common cause of refractory hypokalemia. First-line treatment for Torsades de Pointes is magnesium sulfate 2 g IV regardless of serum level. [11]

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CICM Exam Focus

Key High-Yield Points

1. Hyponatremia correction rate: Maximum 8-10 mmol/L per 24 hours; high-risk patients (alcoholism, malnutrition, hypokalemia) maximum 6 mmol/L per 24 hours [3]
2. 3% saline calculation: 100 mL bolus raises serum sodium by approximately 2 mmol/L; can repeat up to 3 times for severe symptomatic hyponatremia [4]
3. Osmotic demyelination syndrome (ODS): Presents 2-6 days post-correction with dysarthria, dysphagia, quadriparesis; MRI may be initially negative [12]
4. Hyperkalemia ECG progression: Peaked T waves → PR prolongation → P wave flattening → QRS widening → sine wave → VF/asystole [7]
5. Calcium gluconate vs chloride: Gluconate safer peripherally; chloride provides 3x more elemental calcium but requires central access [13]
6. Insulin-dextrose for hyperkalemia: 10 units regular insulin + 25-50 g dextrose; hypoglycemia occurs in 15-20% of patients [14]
7. Free water deficit formula: TBW x [(Current Na/140) - 1]; TBW = 0.6 x weight (males), 0.5 x weight (females) [5]
8. Refractory hypokalemia: Always check and replace magnesium first (Mg acts as ROMK channel "plug") [15]

Common Viva Themes

• Management algorithm for severe symptomatic hyponatremia (Na+ below 120 mmol/L with seizures)
• Preventing osmotic demyelination syndrome: risk factors and rescue therapy
• ECG recognition of hyperkalemia and systematic treatment approach
• Differential diagnosis of hypernatremia in ICU (diabetes insipidus vs osmotic diuresis vs insensible losses)
• Hypocalcemia in massive transfusion and citrate toxicity
• Torsades de Pointes management and role of magnesium
• Phosphate disorders in refeeding syndrome

Common Pitfalls

• Over-correcting hyponatremia (causing ODS) - use desmopressin clamp if overcorrection occurs
• Forgetting to check ionized calcium (total calcium unreliable in hypoalbuminemia/acid-base disturbances)
• Using calcium chloride via peripheral line (causes tissue necrosis)
• Giving dextrose without insulin in hyperglycemic patients (worsens hyperkalemia by osmotic shift)
• Forgetting ongoing losses when calculating free water deficit for hypernatremia
• Not replacing magnesium before potassium in refractory hypokalemia
• Missing hypophosphatemia during refeeding or CRRT

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Key Points

• Electrolyte disorders affect 40-50% of ICU patients; associated with 20-30% increased mortality [1,2]
• Hyponatremia: severe (below 120 mmol/L); 3% saline 100 mL bolus raises Na+ ~2 mmol/L; correct below 8-10 mmol/L/24h [3,4]
• Hypernatremia: free water deficit = TBW x [(Na/140) - 1]; correct below 10 mmol/L/24h [5]
• Hyperkalemia: peaked T waves earliest sign; treat with Ca2+ gluconate, insulin/dextrose, salbutamol, dialysis [7,8]
• Hypokalemia: U waves, ST depression; max IV KCl 10 mmol/h peripheral, 20 mmol/h central [6]
• Ionized calcium (iCa2+) is the only reliable measure in ICU; target greater than 1.1 mmol/L in massive transfusion [9,13]
• Hypomagnesemia causes refractory hypokalemia; MgSO4 2 g IV first-line for Torsades de Pointes [11,15]
• ODS presents 2-6 days after over-rapid sodium correction; high-risk patients need slower correction [12]
• Hypophosphatemia common in refeeding syndrome, sepsis, and CRRT; can cause respiratory muscle weakness [16]

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Epidemiology

Incidence of Electrolyte Disorders in ICU

Electrolyte disturbances are among the most common complications in critically ill patients, with incidence rates substantially higher than in the general hospital population. The pathophysiology involves multiple factors including renal dysfunction, hormonal dysregulation, medication effects, and fluid management.

Sodium disorders: Hyponatremia (Na+ below 135 mmol/L) occurs in 15-30% of ICU admissions, with severe hyponatremia (below 125 mmol/L) in 2-4%. Hypernatremia (Na+ greater than 145 mmol/L) affects 9-26% of ICU patients, often developing during admission (ICU-acquired hypernatremia). Both are independently associated with increased mortality. [1,2,17]

Potassium disorders: Hypokalemia (K+ below 3.5 mmol/L) occurs in 20-40% of critically ill patients, particularly those receiving diuretics, insulin infusions, or with gastrointestinal losses. Hyperkalemia (K+ greater than 5.5 mmol/L) affects 10-15% of ICU patients, with acute kidney injury being the most common cause. [6,18]

Calcium disorders: Ionized hypocalcemia (iCa2+ below 1.0 mmol/L) is present in 15-20% of ICU admissions and up to 80-90% during massive transfusion. Hypercalcemia is less common in ICU (2-5%) but associated with malignancy, immobilization, and hyperparathyroidism. [9,19]

Magnesium disorders: Hypomagnesemia (below 0.7 mmol/L) is highly prevalent, affecting 20-65% of critically ill patients depending on the population studied. It is frequently underdiagnosed as serum levels poorly reflect total body magnesium stores. [11,20]

Phosphate disorders: Hypophosphatemia (below 0.8 mmol/L) occurs in 10-30% of ICU patients, with severe hypophosphatemia (below 0.3 mmol/L) in 2-5%. Risk factors include refeeding syndrome, sepsis, and CRRT. Hyperphosphatemia is common in acute kidney injury and tumor lysis syndrome. [16,21]

Mortality Impact

Electrolyte disorders independently contribute to ICU mortality even after adjustment for severity of illness:

The relationship is often U-shaped for sodium and potassium, with both extremes associated with adverse outcomes. [1,2,17,18]

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Pathophysiology

Sodium Homeostasis

Sodium is the primary determinant of serum osmolality and extracellular fluid volume. Normal serum sodium concentration is 135-145 mmol/L, maintained by the interplay of:

Antidiuretic hormone (ADH/vasopressin): Released from the posterior pituitary in response to hyperosmolality (detected by hypothalamic osmoreceptors) or hypovolemia (detected by baroreceptors). ADH increases water reabsorption in the collecting duct via aquaporin-2 channels, diluting serum sodium. [22]

Thirst mechanism: Primary defense against hypernatremia; impaired in sedated/intubated ICU patients.

Aldosterone: Increases sodium reabsorption in the distal nephron in exchange for potassium secretion.

Atrial natriuretic peptide (ANP): Promotes sodium excretion in response to atrial stretch.

Hyponatremia Mechanisms

Hypovolemic hyponatremia: True sodium and water deficit, but water deficit proportionally less than sodium deficit. Causes include diuretics, vomiting, diarrhea, third-spacing. The body attempts to preserve circulating volume by releasing ADH despite low osmolality ("appropriate" ADH release). [22]

Euvolemic hyponatremia: Water excess with normal or near-normal sodium. The most common cause is Syndrome of Inappropriate ADH (SIADH), where ADH is released inappropriately despite normal or low serum osmolality. Other causes include hypothyroidism, adrenal insufficiency, and medications (SSRIs, carbamazepine, opioids). [23]

Hypervolemic hyponatremia: Both sodium and water excess, but water excess proportionally greater. Seen in heart failure, cirrhosis, and nephrotic syndrome where effective circulating volume is reduced despite total body volume expansion, triggering ADH release. [22]

Cerebral adaptation to hyponatremia: The brain adapts to hypo-osmolality by extruding osmolytes (organic solutes) from cells over 24-48 hours. This adaptation explains why:

1. Chronic hyponatremia may be asymptomatic despite very low sodium levels
2. Rapid correction can cause osmotic demyelination syndrome (ODS) as brain cells cannot rapidly regain osmolytes
3. Acute hyponatremia (below 48 hours) is dangerous because adaptation has not occurred [12]

Hypernatremia Mechanisms

Hypernatremia represents a relative deficit of water compared to sodium:

Pure water deficit: Diabetes insipidus (central or nephrogenic), inadequate water intake (sedated, intubated, elderly patients), increased insensible losses (fever, burns). [5]

Hypotonic fluid loss: Gastrointestinal losses (diarrhea), diuretics, osmotic diuresis (hyperglycemia, mannitol).

Sodium gain: Rare; hypertonic saline administration, sodium bicarbonate therapy, ingestion.

The normal response to hypernatremia is intense thirst and ADH release causing maximal urinary concentration. Failure of these mechanisms (impaired thirst in sedation, inadequate ADH in diabetes insipidus, kidney resistance to ADH in nephrogenic DI) leads to progressive hypernatremia. [5]

Potassium Homeostasis

Potassium is the principal intracellular cation (intracellular concentration ~150 mmol/L vs extracellular ~4 mmol/L). This 40:1 gradient is maintained by Na+/K+-ATPase and is critical for:

• Cardiac action potential and electrical stability
• Skeletal muscle function
• Neuronal excitability

Small changes in extracellular potassium profoundly affect the resting membrane potential, explaining the cardiac and neuromuscular manifestations of dyskalemia. [6]

Hypokalemia Mechanisms

Transcellular shift (redistribution into cells):

• Insulin (stimulates Na+/K+-ATPase)
• Beta-2 agonists (catecholamines, salbutamol)
• Alkalosis (H+ leaves cells, K+ enters to maintain electroneutrality)
• Hypothermia

Renal losses:

• Diuretics (loop and thiazide diuretics increase distal sodium delivery and flow)
• Hyperaldosteronism (primary or secondary)
• Hypomagnesemia (loss of ROMK channel inhibition)
• Renal tubular acidosis

Gastrointestinal losses: Diarrhea, vomiting (primarily renal loss from metabolic alkalosis and volume depletion-induced aldosterone release), nasogastric suction.

Inadequate intake: Rare as sole cause but contributes in anorexia, alcoholism. [6,15]

Hyperkalemia Mechanisms

Decreased renal excretion (most common):

• Acute kidney injury (GFR below 20 mL/min)
• Chronic kidney disease
• Potassium-sparing diuretics (spironolactone, amiloride)
• ACE inhibitors/ARBs (reduced aldosterone)
• Hypoaldosteronism (Addison's disease, diabetic nephropathy)

Transcellular shift (redistribution out of cells):

• Acidosis (H+ enters cells, K+ exits)
• Insulin deficiency (diabetic ketoacidosis)
• Beta-blockers
• Cell lysis (rhabdomyolysis, tumor lysis syndrome, hemolysis)
• Hypertonicity (water shifts from cells, potassium follows)
• Succinylcholine (in susceptible patients)

Increased intake: Rare as sole cause with normal renal function; iatrogenic (excessive IV potassium, potassium penicillin). [7,8]

Calcium Homeostasis

Calcium exists in three forms in plasma:

• Ionized (free) calcium (iCa2+): ~50%, the physiologically active fraction
• Protein-bound (primarily albumin): ~40%
• Complexed to anions (citrate, phosphate, lactate): ~10%

Normal ionized calcium: 1.1-1.3 mmol/L. Total calcium is affected by albumin concentration and acid-base status, making it unreliable in ICU patients. Only ionized calcium should guide clinical decisions. [9,13]

Parathyroid hormone (PTH): Released in response to low iCa2+; increases bone resorption, renal calcium reabsorption, and 1,25-dihydroxyvitamin D synthesis.

Vitamin D: Increases intestinal calcium absorption and bone mobilization.

Calcitonin: Released from thyroid C cells in response to high calcium; inhibits bone resorption (minor role).

Hypocalcemia Mechanisms

Citrate toxicity: During massive transfusion, citrate anticoagulant in blood products chelates ionized calcium. One unit of PRBCs contains ~3 g citrate. With rapid transfusion (greater than 1 unit per 5 minutes), hepatic citrate metabolism is overwhelmed, causing acute hypocalcemia. The "lethal diamond" extends the traditional lethal triad (hypothermia, acidosis, coagulopathy) to include hypocalcemia as the fourth factor. [13,19]

Other ICU causes:

• Hypoparathyroidism (post-thyroidectomy)
• Vitamin D deficiency
• Sepsis (cytokine-mediated PTH resistance)
• Pancreatitis (saponification of fat)
• Hypomagnesemia (impairs PTH secretion and action)
• Alkalosis (increases protein binding, reduces iCa2+)
• Rhabdomyolysis (calcium sequestration in damaged muscle)
• Tumor lysis syndrome (hyperphosphatemia causes calcium-phosphate precipitation)

Hypercalcemia Mechanisms

Malignancy (most common cause in hospitalized patients):

• PTH-related peptide (PTHrP) secretion (lung, breast, renal cell carcinoma)
• Osteolytic metastases
• 1,25-vitamin D production (lymphoma)

Primary hyperparathyroidism: Most common outpatient cause; parathyroid adenoma.

Other causes: Immobilization, vitamin D intoxication, thiazide diuretics, granulomatous disease, milk-alkali syndrome. [10]

Magnesium Homeostasis

Magnesium is the second most abundant intracellular cation. Serum concentration (0.7-1.0 mmol/L) represents only 0.3% of total body magnesium, making it a poor indicator of total body stores. [11,20]

Functions:

• Cofactor for greater than 300 enzymatic reactions (including ATP-dependent processes)
• Stabilizes cardiac cell membranes (blocks L-type calcium channels, inhibits early afterdepolarizations)
• Essential for PTH secretion and action
• Acts as "plug" in ROMK channels, preventing renal potassium wasting

Hypomagnesemia Mechanisms

Renal losses: Diuretics (loop and thiazide), aminoglycosides, amphotericin B, cisplatin, cyclosporine, CRRT.

Gastrointestinal losses: Diarrhea, malabsorption, proton pump inhibitors (impair intestinal absorption).

Transcellular shift: Refeeding syndrome, insulin therapy, catecholamines.

Critical illness: Sepsis (cytokine-mediated redistribution), burns, hypothermia. [11,15,20]

Phosphate Homeostasis

Phosphate is essential for ATP synthesis, 2,3-DPG (oxygen delivery), cell membrane integrity, and bone minerite. Normal serum phosphate: 0.8-1.5 mmol/L. [16,21]

Hypophosphatemia mechanisms:

• Transcellular shift: Refeeding syndrome, insulin administration, respiratory alkalosis
• Decreased absorption: Malnutrition, phosphate binders
• Increased losses: CRRT, diuretics, hyperparathyroidism

Hyperphosphatemia mechanisms:

• Decreased excretion: Acute kidney injury, chronic kidney disease
• Increased release: Tumor lysis syndrome, rhabdomyolysis
• Increased intake: Phosphate-containing enemas

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Clinical Presentation

Hyponatremia

Clinical manifestations depend on severity, rate of development, and patient factors. Chronic hyponatremia may be asymptomatic despite very low sodium levels due to cerebral adaptation.

Mild hyponatremia (130-135 mmol/L): Often asymptomatic; may have subtle cognitive impairment, gait instability (increased falls risk in elderly). [3]

Moderate hyponatremia (120-130 mmol/L): Headache, nausea, fatigue, confusion, muscle cramps.

Severe hyponatremia (below 120 mmol/L):

• Neurological: Seizures, altered consciousness, coma
• Respiratory: Cheyne-Stokes breathing, respiratory arrest
• Brain herniation in acute cases (cerebral edema)

Acute vs chronic distinction:

• Acute (below 48 hours): High risk of cerebral edema, seizures, herniation
• Chronic (greater than 48 hours): Lower acute risk due to adaptation, but higher risk of ODS with rapid correction [4,12]

Hypernatremia

Symptoms reflect cellular dehydration, particularly affecting the brain.

Mild hypernatremia (145-150 mmol/L): Thirst (if conscious), dry mucous membranes, oliguria.

Moderate hypernatremia (150-160 mmol/L): Lethargy, irritability, weakness, hyperreflexia.

Severe hypernatremia (greater than 160 mmol/L):

• Confusion, seizures, coma
• Subdural or subarachnoid hemorrhage (brain shrinkage tears bridging veins)
• Rhabdomyolysis
• Mortality greater than 50% when Na+ greater than 160 mmol/L [5,17]

Hypokalemia

ECG changes (correlate poorly with serum level):

• U waves (most characteristic, after T wave)
• ST segment depression
• T wave flattening or inversion
• Prolonged PR interval
• Increased P wave amplitude
• Wide QRS (severe)

Cardiac: Increased risk of atrial and ventricular arrhythmias, particularly in patients on digoxin or with underlying heart disease.

Neuromuscular: Weakness (proximal > distal), hyporeflexia, paralysis (severe), rhabdomyolysis (severe).

Gastrointestinal: Ileus, constipation.

Metabolic: Impaired insulin release (hyperglycemia), metabolic alkalosis, polyuria (nephrogenic DI-like state). [6]

Hyperkalemia

ECG changes (progressive with increasing K+):

Important: ECG changes correlate with rate of rise as much as absolute level. Chronic hyperkalemia may have minimal ECG changes.

Neuromuscular: Weakness (ascending, may progress to respiratory failure), paresthesias.

Cardiac: Bradyarrhythmias, heart block, ventricular fibrillation, asystole.

Note: Hyperkalemia is the electrolyte emergency most likely to cause sudden cardiac death. [7,8]

Hypocalcemia

Neuromuscular (due to increased neuronal excitability):

• Tetany: carpopedal spasm, laryngospasm
• Paresthesias (perioral, fingers, toes)
• Chvostek sign (facial twitching on tapping facial nerve)
• Trousseau sign (carpopedal spasm on inflating BP cuff)
• Seizures (severe)

Cardiac:

• Prolonged QT interval (risk of Torsades de Pointes)
• Heart failure (impaired contractility)
• Hypotension (refractory to vasopressors)

Other: Bronchospasm, bowel hypermotility. [9,10]

Hypercalcemia

The classic mnemonic "bones, stones, abdominal groans, and psychic moans":

Neuropsychiatric ("psychic moans"): Lethargy, confusion, depression, coma.

Gastrointestinal ("abdominal groans"): Nausea, vomiting, constipation, pancreatitis.

Renal ("stones"): Nephrolithiasis, nephrogenic DI (polyuria, polydipsia), AKI.

Skeletal ("bones"): Bone pain, pathological fractures.

Cardiac: Shortened QT interval, J wave (Osborn wave), bradycardia, digitalis sensitivity.

Severe hypercalcemia (greater than 3.5 mmol/L): Medical emergency; cardiac arrest possible. [10]

Hypomagnesemia

Often clinically silent or non-specific. Consider in:

• Refractory hypokalemia (not responding to potassium replacement)
• Refractory hypocalcemia
• Cardiac arrhythmias (atrial fibrillation, Torsades de Pointes)
• Weakness, tremor, hyperreflexia, tetany
• Seizures (severe)

Critical feature: Hypomagnesemia should be suspected and treated whenever hypokalemia or hypocalcemia is resistant to replacement therapy. [11,15]

Hypophosphatemia

Mild (0.5-0.8 mmol/L): Often asymptomatic.

Moderate (0.3-0.5 mmol/L): Weakness, confusion, paresthesias.

Severe (below 0.3 mmol/L):

• Respiratory failure (diaphragm weakness) - may impair weaning from ventilation
• Cardiac dysfunction, arrhythmias
• Rhabdomyolysis
• Hemolysis (red cell ATP depletion)
• Seizures
• Coma

High-risk setting: Refeeding syndrome - phosphate shifts intracellularly with glucose/insulin administration in malnourished patients. [16,21]

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Investigations

Laboratory Assessment

Essential electrolyte panel:

• Sodium, potassium, chloride, bicarbonate
• Ionized calcium (NOT total calcium in ICU patients)
• Magnesium, phosphate
• Urea, creatinine (assess renal function)
• Glucose (affects sodium: pseudohyponatremia with hyperglycemia)

Serum osmolality:

• Measured osmolality: Normal 280-295 mOsm/kg
• Calculated osmolality: 2 x [Na+] + [Glucose] + [Urea] (all in mmol/L)
• Osmolar gap: Measured - Calculated (normal below 10 mOsm/kg)

Urine studies (for sodium disorders):

• Urine osmolality
• Urine sodium
• Urine potassium (if hypokalemia)

Hyponatremia Workup

Step 1: Confirm true hyponatremia (exclude pseudohyponatremia)

• Measure serum osmolality
• If low (below 280 mOsm/kg): True hypotonic hyponatremia
• If normal/high: Consider hyperglycemia (correct Na+: add 1.6 mmol/L Na+ for every 5.5 mmol/L glucose above normal), hyperlipidemia, paraproteinemia

Step 2: Assess volume status (clinical examination, urine studies)

• Urine osmolality below 100 mOsm/kg: Primary polydipsia, beer potomania, reset osmostat
• Urine osmolality greater than 100 mOsm/kg: Assess urine sodium

Step 3: Interpret urine sodium

Additional investigations:

• Thyroid function tests (TSH, free T4)
• Morning cortisol (if adrenal insufficiency suspected)
• Chest X-ray (SIADH causes: lung malignancy, pneumonia)
• CT head (if neurological symptoms or CNS cause of SIADH suspected)

Hypernatremia Workup

Assess urine output and osmolality:

Water deprivation test (if diabetes insipidus suspected):

• Rarely needed in ICU (clinical context usually sufficient)
• Response to desmopressin distinguishes central (responds) from nephrogenic (no response) DI

Potassium Disorder Workup

Hypokalemia:

• Urine potassium below 20 mmol/L: Extrarenal loss (GI) or transcellular shift
• Urine potassium greater than 20 mmol/L: Renal loss
• Always check magnesium
• Assess acid-base status

Hyperkalemia:

• Exclude pseudohyperkalemia (hemolyzed sample, leukocytosis, thrombocytosis)
• ECG (urgency assessment)
• Renal function
• Medications review (ACE-I, ARB, K+-sparing diuretics)
• Consider rhabdomyolysis (CK), tumor lysis (uric acid, LDH, phosphate), adrenal insufficiency

Calcium Disorder Workup

Always measure ionized calcium in ICU patients. Total calcium is unreliable due to:

• Hypoalbuminemia (common in ICU - causes low total, normal ionized)
• Acid-base disturbances (acidosis increases ionized fraction)
• Citrate (massive transfusion, CRRT with citrate anticoagulation)

Hypocalcemia workup:

• PTH level (low: hypoparathyroidism; high: vitamin D deficiency, resistance)
• 25-hydroxyvitamin D
• Magnesium (low Mg impairs PTH secretion)
• Phosphate (high: renal failure, tumor lysis; normal: hypoparathyroidism)
• Albumin

Hypercalcemia workup:

• PTH level (elevated: primary hyperparathyroidism; suppressed: malignancy, vitamin D)
• PTH-related peptide (PTHrP)
• 1,25-dihydroxyvitamin D
• Cancer screening (if indicated)
• Protein electrophoresis (if myeloma suspected)

ECG in Electrolyte Disorders

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Management

Hyponatremia Management

Severe Symptomatic Hyponatremia (Emergency)

Indication: Na+ below 120 mmol/L with seizures, altered consciousness, or signs of brain herniation.

Initial treatment (regardless of etiology):

1. 3% Hypertonic saline 100 mL IV bolus over 10 minutes
2. Check sodium at 20-30 minutes
3. Repeat bolus (up to 3 times, total 300 mL) until:
   • Symptoms improve, OR
   • Sodium rises by 4-6 mmol/L

Rationale: 100 mL of 3% saline raises serum sodium by approximately 2 mmol/L. A 4-6 mmol/L rise is usually sufficient to reduce intracranial pressure and stop seizures without exceeding 24-hour limits. [3,4]

Preparation of 3% saline: Add 30 mL of 23.4% NaCl to 1 L of 0.9% NaCl = approximately 3% saline.

Correction Rate Limits

To prevent osmotic demyelination syndrome, correction must be controlled:

High-risk factors for ODS:

• Serum sodium ≤105 mmol/L
• Hypokalemia (potassium replacement also raises sodium!)
• Alcoholism, malnutrition
• Advanced liver disease
• Chronicity greater than 48 hours (or unknown duration) [12]

Desmopressin Clamp Strategy

To maintain precise control of sodium correction:

1. Start desmopressin (dDAVP) 1-2 mcg IV every 6-8 hours

   • This "clamps" urine output, preventing unpredictable water diuresis
   • The kidney cannot excrete free water regardless of underlying cause

2. Administer 3% saline at controlled rate

   • Typically 15-30 mL/h, adjusted based on sodium checks

3. Monitor sodium every 2-4 hours and adjust saline rate

Advantage: Prevents overcorrection that often occurs when underlying cause resolves (e.g., SIADH resolving, volume depletion corrected) causing sudden water diuresis. [3]

Rescue Therapy for Overcorrection

If sodium rises greater than 10-12 mmol/L in 24 hours:

1. Stop all sodium replacement immediately
2. Start D5W (5% dextrose) at 3-10 mL/kg/hour
3. Give desmopressin 2 mcg IV to stop free water loss
4. Target: Re-lower sodium to within the safe correction range

Early intervention may prevent ODS development. [4]

Volume Status-Directed Therapy

Hypovolemic hyponatremia:

• Primary treatment: 0.9% normal saline to restore volume
• Caution: Rapid correction may occur when ADH suppressed after volume restoration
• Consider desmopressin clamp if high ODS risk

Euvolemic hyponatremia (SIADH):

• Fluid restriction (1-1.5 L/day) for mild cases
• Salt tablets + loop diuretic for moderate cases
• Hypertonic saline for severe/symptomatic
• Tolvaptan (vasopressin V2 receptor antagonist) - restricted use, requires monitoring

Hypervolemic hyponatremia (heart failure, cirrhosis):

• Treat underlying condition
• Fluid and sodium restriction
• Diuretics
• Hypertonic saline rarely needed (only for severe symptoms)

Hypernatremia Management

Free Water Deficit Calculation

\text{Free Water Deficit (L)} = \text{TBW} \times \left( \frac{\text{Current Na}}{140} - 1 \right)

Total Body Water (TBW):

• Young males: 0.6 x body weight (kg)
• Young females: 0.5 x body weight (kg)
• Elderly males: 0.5 x body weight (kg)
• Elderly females: 0.45 x body weight (kg)

Example: 70 kg male with Na+ 160 mmol/L

• TBW = 0.6 x 70 = 42 L
• FWD = 42 x [(160/140) - 1] = 42 x 0.14 = 6 L

Critical note: This calculates the STATIC deficit. Ongoing losses (urine, insensible) must be added to the replacement volume. [5]

Correction Rate

• Chronic hypernatremia (greater than 48 hours): Maximum 10 mmol/L per 24 hours

  • "Correction rate: ~0.5 mmol/L per hour"
  • Faster correction risks cerebral edema (brain has accumulated idiogenic osmoles)

• Acute hypernatremia (below 48 hours): Can correct more rapidly (1-2 mmol/L per hour)

  • Brain has not yet adapted

Fluid Choice

Preferred route: Enteral water via nasogastric tube (most physiological).

Diabetes Insipidus Management

Central DI (ADH deficiency):

• Desmopressin (dDAVP) 1-4 mcg IV/SC every 12-24 hours
• Titrate to urine output (target 1-2 mL/kg/h)
• Continue free water replacement alongside

Nephrogenic DI (ADH resistance):

• Address underlying cause (lithium, hypercalcemia, hypokalemia)
• Low-solute diet
• Thiazide diuretics (paradoxically reduce urine output)
• NSAIDs (reduce prostaglandin-mediated ADH resistance) [5]

Hypokalemia Management

Assessment of Severity

Replacement Routes

Oral potassium (preferred if absorbing):

• Potassium chloride 40-80 mmol/day in divided doses
• Slow release preparations reduce GI irritation

Intravenous potassium:

Calculation: Each 10 mmol IV KCl raises serum K+ by approximately 0.1 mmol/L.

Monitoring: Check potassium after every 40-60 mmol replaced.

Critical Steps

1. Check and replace magnesium first

   • Hypomagnesemia causes refractory hypokalemia
   • Aim for Mg2+ greater than 0.8 mmol/L

2. Assess and treat underlying cause

   • Stop offending medications (diuretics if possible)
   • Treat GI losses, correct alkalosis

3. Continuous ECG monitoring for severe hypokalemia

4. Avoid glucose-only infusions (insulin release drives K+ intracellularly) [6,15]

Hyperkalemia Management

Hyperkalemia greater than 6.5 mmol/L with ECG changes is a medical emergency.

Treatment Algorithm

Step 1: Membrane Stabilization (Immediate)

Important: Calcium does NOT lower potassium. It stabilizes the cardiac membrane, reducing arrhythmia risk. Can repeat if ECG changes persist.

Step 2: Intracellular Shift

Notes on insulin-dextrose:

• Monitor glucose closely - hypoglycemia occurs in 15-20% of patients
• If glucose greater than 250 mg/dL (14 mmol/L), insulin alone may suffice
• Some protocols use 5-6 units insulin to reduce hypoglycemia risk [14]

Sodium bicarbonate: Only effective if concurrent metabolic acidosis; not first-line in absence of acidosis.

Step 3: Elimination

Hemodialysis indications:

• K+ greater than 6.5 mmol/L unresponsive to medical therapy
• Severe ECG changes
• Acute kidney injury/ESRD [7,8]

Calcium Disorders Management

Hypocalcemia Treatment

Severe/symptomatic (iCa2+ below 0.8 mmol/L with symptoms):

Maintenance infusion: Calcium gluconate 10% 50-100 mL (5-10 g) in 500 mL D5W at 50 mL/hour. Adjust to maintain iCa2+ greater than 1.0 mmol/L.

Important considerations:

• Check and replace magnesium (required for PTH action)
• In massive transfusion: Give calcium gluconate 1 g for every 4 units of blood products [13,19]
• Avoid IV calcium if patient on digoxin (risk of fatal arrhythmia)
• Correct alkalosis if present (reduces ionized fraction)

Oral replacement (stable patients): Calcium carbonate 500-1000 mg TDS + vitamin D if deficient.

Hypercalcemia Treatment

Severe hypercalcemia (Ca2+ greater than 3.5 mmol/L or symptomatic):

Step 1: Volume resuscitation

• 0.9% NaCl 200-300 mL/hour initially (3-6 L in first 24 hours)
• Increases renal calcium excretion
• Monitor for fluid overload

Step 2: Loop diuretics (after volume replete)

• Furosemide 20-40 mg IV every 6-12 hours
• Enhances calciuresis
• Do NOT give before volume repletion (worsens dehydration)

Step 3: Bisphosphonates (effect in 2-4 days)

• Zoledronic acid 4 mg IV over 15 minutes, OR
• Pamidronate 60-90 mg IV over 2-4 hours
• Contraindicated if GFR below 30 mL/min

Step 4: Calcitonin (rapid but transient effect)

• Salmon calcitonin 4 IU/kg SC/IM every 12 hours
• Onset 4-6 hours; tachyphylaxis develops within 48 hours

Step 5: Dialysis - if refractory or renal failure prevents other therapies

Other treatments:

• Denosumab: For bisphosphonate-refractory cases
• Glucocorticoids: For vitamin D-mediated hypercalcemia (granulomatous disease, lymphoma)
• Cinacalcet: For primary hyperparathyroidism if surgery not feasible [10]

Magnesium Disorders Management

Hypomagnesemia Treatment

Torsades de Pointes (regardless of Mg level):

• Magnesium sulfate 2 g IV bolus over 1-2 minutes
• Follow with 2-4 g over 24 hours

Severe hypomagnesemia (below 0.5 mmol/L):

• Magnesium sulfate 4-8 g IV over 8-24 hours
• Maximum rate 1 g/hour (faster rates can cause flushing, hypotension)

Moderate hypomagnesemia (0.5-0.7 mmol/L):

• Magnesium sulfate 2-4 g IV over 4-8 hours

Mild hypomagnesemia (0.7-0.8 mmol/L):

• Oral magnesium if tolerating (magnesium oxide 400 mg TDS)
• IV if NPO or unreliable absorption

Monitoring: Check magnesium 12-24 hours after replacement.

Caution in renal impairment: Reduce dose by 50% if GFR below 30 mL/min; monitor for hypermagnesemia (loss of reflexes, respiratory depression). [11,20]

Phosphate Disorders Management

Hypophosphatemia Treatment

IV preparations:

• Sodium phosphate: 94 mmol Na+ per 100 mmol phosphate
• Potassium phosphate: 170 mmol K+ per 100 mmol phosphate (use if also hypokalemic)

Maximum IV rate: 7 mmol/hour (risk of hypocalcemia from calcium-phosphate precipitation).

Monitoring: Recheck phosphate and calcium after replacement.

Refeeding syndrome prevention:

• Start nutrition slowly in malnourished patients
• Prophylactic phosphate, potassium, magnesium, thiamine before feeding [16,21]

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Osmotic Demyelination Syndrome (ODS)

Pathophysiology

ODS (formerly central pontine myelinolysis, CPM) occurs when chronic hyponatremia is corrected too rapidly. During chronic hyponatremia, brain cells adapt by extruding organic osmolytes (glutamate, myo-inositol, taurine) to maintain cellular volume. Rapid correction of serum sodium creates a hyperosmolar extracellular environment that the adapted cells cannot rapidly equilibrate with, causing:

1. Cellular shrinkage and dehydration
2. Oligodendrocyte injury and apoptosis
3. Demyelination (classically in the pons, but extrapontine involvement in 50%)

Risk is highest when correction exceeds 8-12 mmol/L in 24 hours, particularly in high-risk patients. [12]

Clinical Presentation

Timing: Symptoms appear 2-6 days after rapid sodium correction.

Initial phase (during correction): Apparent improvement in hyponatremia symptoms.

Delayed phase (2-6 days later):

• Dysarthria, dysphagia
• Quadriparesis (spastic)
• "Locked-in syndrome" (severe cases - aware but unable to move except for vertical eye movements)
• Behavioral changes, confusion
• Movement disorders (extrapontine involvement)

Diagnosis

MRI brain:

• May be initially normal (changes lag behind symptoms by 2 weeks)
• T2/FLAIR hyperintensity in central pons ("trident" or "bat-wing" pattern)
• Extrapontine lesions: Basal ganglia, thalamus, cerebellum, cortex

CSF: Usually normal or mild protein elevation.

Treatment

There is no proven treatment for established ODS. Management is supportive:

• Intensive rehabilitation (physio, speech therapy)
• Prevention of complications (aspiration, pressure sores, DVT)
• Some case reports suggest re-lowering sodium after overcorrection may prevent or mitigate ODS if done early

Prognosis: Variable; 30-40% mortality historically, but some patients make remarkable recoveries over months. Early recognition of overcorrection and re-lowering may improve outcomes. [12]

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Special Considerations

Electrolyte Disorders in Massive Transfusion

Massive transfusion (greater than 10 units PRBCs in 24 hours or greater than 4 units in 1 hour) causes predictable electrolyte disturbances:

Hypocalcemia (citrate toxicity):

• Citrate anticoagulant in blood products chelates ionized calcium
• Most pronounced with FFP (higher citrate content than PRBCs)
• Monitor iCa2+ every 15-30 minutes during active transfusion
• Replace: Calcium gluconate 1 g (or calcium chloride 300 mg) for every 4 units transfused
• Target iCa2+ greater than 1.1 mmol/L [13,19]

Hyperkalemia:

• Stored blood has elevated potassium (up to 50 mmol/L in older units)
• Usually transient; potassium is rapidly redistributed
• May be significant in rapid transfusion, hypothermia, or renal impairment
• Monitor and treat as needed

Hypocalcemia contributes to coagulopathy: Calcium is Factor IV in the coagulation cascade. The "lethal diamond" (hypothermia, acidosis, coagulopathy, hypocalcemia) perpetuates bleeding.

Electrolyte Disorders in CRRT

Continuous renal replacement therapy significantly affects electrolytes:

Hypophosphatemia: Most common electrolyte abnormality during CRRT (phosphate is effectively cleared). Requires regular monitoring and replacement.

Hypokalemia and hypomagnesemia: Also cleared effectively; require supplementation in replacement fluids or separate infusions.

Hypocalcemia (with citrate anticoagulation): Citrate chelates calcium; requires calcium replacement infusion (typically via separate central line). Monitor iCa2+ every 4-6 hours. Target systemic iCa2+ 1.0-1.2 mmol/L.

Citrate accumulation: In liver failure, citrate metabolism is impaired, causing:

• Rising total calcium (citrate-calcium complex)
• Low ionized calcium (citrate chelation)
• Total:ionized calcium ratio greater than 2.5 suggests citrate accumulation
• Treatment: Switch to heparin anticoagulation, reduce citrate infusion

Refeeding Syndrome

Refeeding syndrome occurs when nutrition is reintroduced in malnourished patients, causing life-threatening electrolyte shifts:

Pathophysiology:

• During starvation, body shifts to fat/protein catabolism
• Insulin secretion is low; intracellular electrolyte stores are depleted
• Refeeding stimulates insulin release, driving glucose AND electrolytes (K+, PO4, Mg2+) into cells
• Thiamine is also depleted (cofactor for glucose metabolism)

High-risk patients:

• BMI below 16 kg/m2
• Unintentional weight loss greater than 15% in 3-6 months
• Little/no nutrition for greater than 10 days
• Low K+, PO4, or Mg2+ before feeding
• History of alcohol abuse, chemotherapy, antacids

Prevention:

1. Identify at-risk patients
2. Check and replace electrolytes BEFORE feeding
3. Give thiamine 200-300 mg IV before first feed
4. Start nutrition slowly (10-20 kcal/kg/day, increase over 4-7 days)
5. Monitor electrolytes daily for first week [16]

Drug-Induced Electrolyte Disorders

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CICM Exam Practice

SAQ 1: Severe Hyponatremia Management

Question: A 62-year-old woman with small cell lung cancer is admitted to ICU with a witnessed seizure. Her serum sodium is 112 mmol/L. She has been unwell for several weeks with poor oral intake.

(a) Outline your immediate management of this patient. (4 marks) (b) Describe the principles guiding the rate of sodium correction and the rationale. (4 marks) (c) Outline the clinical features and pathophysiology of osmotic demyelination syndrome. (4 marks)

Model Answer:

(a) Immediate management (4 marks):

Airway and resuscitation:

• Protect airway if ongoing seizure or GCS impaired
• Administer oxygen, establish IV access
• Benzodiazepine if actively seizing (lorazepam 4 mg IV or midazolam 5 mg IM)

Hypertonic saline for severe symptomatic hyponatremia:

• 3% hypertonic saline 100 mL IV bolus over 10 minutes
• Recheck sodium at 20-30 minutes
• Repeat bolus (up to 3 times, total 300 mL) until:
  • Seizures stop, OR
  • Sodium rises by 4-6 mmol/L (usually sufficient to reduce cerebral edema)
• 100 mL of 3% saline raises sodium by approximately 2 mmol/L

Monitoring:

• ICU admission with continuous monitoring
• Frequent neurological assessment
• Serum sodium every 2-4 hours during acute phase

(b) Principles of correction rate (4 marks):

Correction limits:

• Maximum 8-10 mmol/L in first 24 hours for standard-risk patients
• Maximum 6 mmol/L in 24 hours for high-risk patients (this patient - chronic hyponatremia, malnutrition/malignancy)
• Maximum 18 mmol/L in 48 hours

Rationale (prevention of osmotic demyelination syndrome):

• In chronic hyponatremia (greater than 48 hours), brain cells adapt by extruding organic osmolytes (glutamate, myo-inositol, taurine)
• This protects against cerebral edema despite low serum osmolality
• Rapid correction creates hyperosmolar extracellular environment
• Brain cells cannot rapidly regain osmolytes, causing cellular shrinkage
• This leads to oligodendrocyte injury and demyelination, particularly in the pons

Desmopressin clamp strategy:

• Consider desmopressin 1-2 mcg IV every 6-8 hours to prevent unpredictable water diuresis
• Allows controlled correction with 3% saline
• Particularly important when underlying cause may resolve (causing sudden aquaresis)

(c) Osmotic demyelination syndrome (4 marks):

Timing and clinical features:

• Onset 2-6 days after rapid sodium correction
• Often preceded by initial improvement in hyponatremia symptoms
• Classic features:
  • Dysarthria and dysphagia (pseudobulbar palsy)
  • Quadriparesis (spastic)
  • "Locked-in syndrome" in severe cases (awareness preserved, only vertical eye movements possible)
  • Behavioral changes, confusion
  • Movement disorders (if extrapontine involvement)

Pathophysiology:

• Chronic adaptation to hyponatremia involves extrusion of organic osmolytes from brain cells
• Rapid correction creates hyperosmolar extracellular environment
• Osmotic stress causes oligodendrocyte apoptosis and demyelination
• Central pons is most vulnerable (watershed zone between pontine and basilar artery territories)
• Extrapontine structures (basal ganglia, thalamus) affected in ~50%

MRI findings:

• May be initially negative (changes lag symptoms by ~2 weeks)
• T2/FLAIR hyperintensity in central pons ("trident" or "bat-wing" pattern)

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SAQ 2: Hyperkalemia Emergency

Question: A 58-year-old male with type 2 diabetes and chronic kidney disease (eGFR 25 mL/min) is admitted with community-acquired pneumonia. His potassium is 7.2 mmol/L. The ECG shows peaked T waves and widened QRS complexes.

(a) List the ECG changes associated with progressive hyperkalemia. (3 marks) (b) Outline your emergency management of this patient, including doses. (6 marks) (c) Discuss the mechanism of action of each treatment modality. (3 marks)

Model Answer:

(a) ECG changes with progressive hyperkalemia (3 marks):

Sequential progression with increasing potassium:

• 5.5-6.5 mmol/L: Peaked T waves (tall, narrow, symmetrical, "tented")
• 6.5-7.5 mmol/L: PR interval prolongation, P wave flattening/loss
• 7.5-8.0 mmol/L: QRS widening (greater than 120 ms)
• greater than 8.0 mmol/L: Sine wave pattern (fusion of widened QRS and T wave)
• Terminal: Ventricular fibrillation or asystole

Important note: ECG changes correlate with rate of rise as much as absolute level; chronic hyperkalemia may have minimal ECG changes despite high levels.

(b) Emergency management (6 marks):

Step 1: Membrane Stabilization (First Priority)

• Calcium gluconate 10%: 10 mL (1 g) IV over 5-10 minutes
• Effect begins within 1-3 minutes, lasts 30-60 minutes
• Can repeat if ECG changes persist after 5 minutes
• Does NOT lower potassium; stabilizes cardiac membrane to reduce arrhythmia risk
• (Alternatively: Calcium chloride 10% 10 mL via central line - provides 3x more elemental calcium)

Step 2: Intracellular Shift

• Insulin and dextrose: 10 units regular insulin IV + 50 mL of 50% dextrose (25 g)

• Onset 10-20 minutes, duration 4-6 hours

• Lowers K+ by 0.6-1.0 mmol/L

• Monitor glucose closely (hypoglycemia in 15-20%)

• Salbutamol nebulized: 10-20 mg via nebulizer

• Onset 30 minutes, duration 2 hours

• Lowers K+ by 0.5-1.0 mmol/L

• Use as adjunct to insulin (synergistic effect)

• Sodium bicarbonate: 50-100 mmol IV

• Only if concurrent metabolic acidosis (pH below 7.2)

• Less effective than insulin; not first-line in absence of acidosis

Step 3: Elimination

• Dialysis: Arrange urgent hemodialysis (this patient has CKD eGFR 25 and is unlikely to respond adequately to diuretics)
• Dialysis is definitive treatment for refractory hyperkalemia in renal impairment
• Until dialysis available, continue Step 2 therapies

Monitoring:

• Continuous ECG monitoring
• Repeat potassium in 1-2 hours after initial treatment
• Monitor glucose every 30-60 minutes if insulin given

(c) Mechanism of action (3 marks):

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Viva Scenarios

Viva 1: Hypernatremia in Neurosurgical Patient

Examiner: A 45-year-old male is 3 days post-clipping of a ruptured anterior communicating artery aneurysm. He develops polyuria (400 mL/hour) and his sodium is 158 mmol/L. Tell me about your approach.

Candidate response:

This presentation is highly concerning for central diabetes insipidus (DI) following neurosurgery affecting the hypothalamic-pituitary axis.

Immediate assessment:

• Confirm polyuria with dilute urine (urine osmolality below 300 mOsm/kg is characteristic of DI)
• Check serum osmolality (will be elevated, greater than 295 mOsm/kg)
• Assess volume status clinically
• Review fluid balance chart

Differential diagnosis of polyuria post-neurosurgery:

• Central diabetes insipidus (most likely - damage to ADH-producing neurons or pituitary stalk)
• Osmotic diuresis (mannitol, glucose, urea)
• Cerebral salt wasting (associated with hyponatremia, not hypernatremia)
• Polyuric phase of ATN recovery

Examiner: The urine osmolality is 120 mOsm/kg. How do you manage this?

Candidate response:

This confirms central diabetes insipidus (urine cannot be concentrated despite hyperosmolar serum).

Calculate free water deficit:

• TBW = 0.6 x 80 kg = 48 L
• FWD = 48 x [(158/140) - 1] = 48 x 0.13 = 6.2 L

Correction rate:

• This is acute hypernatremia (below 48 hours) so can correct more rapidly
• However, maximum 10-12 mmol/L in first 24 hours remains prudent
• Target: Reduce sodium by 0.5 mmol/L per hour to ~148 mmol/L in first 24 hours

Treatment:

1. Replace ongoing losses:

   • Match urine output mL-for-mL with D5W or enteral free water
   • If urine output 400 mL/hour, need 400 mL/hour replacement

2. Replace calculated deficit:

   • 6.2 L over 24-48 hours = ~250-130 mL/hour additional

3. Desmopressin (dDAVP):

   • Give 1-2 mcg IV or SC every 12-24 hours
   • This will reduce urine output and allow controlled correction
   • Titrate to urine output 2-3 mL/kg/hour

4. Monitoring:

   • Serum sodium every 4-6 hours
   • Strict input/output charting
   • Urine osmolality to confirm response to dDAVP

Examiner: What are the risks if you correct too rapidly?

Candidate response:

In hypernatremia, rapid correction risks cerebral edema rather than ODS (which occurs in rapid hyponatremia correction).

During chronic hypernatremia, brain cells accumulate idiogenic osmoles (organic solutes) to prevent cellular dehydration. If serum sodium is corrected too rapidly, water shifts into brain cells before they can extrude these osmolytes, causing cellular swelling and cerebral edema.

Clinically this manifests as:

• Headache, nausea, vomiting
• Altered consciousness, confusion
• Seizures
• Coma
• Potentially fatal brain herniation

This is more of a concern in children than adults, and in chronic (greater than 48 hours) hypernatremia. However, limiting correction to 10-12 mmol/L per 24 hours remains the standard recommendation.

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Viva 2: Torsades de Pointes and Magnesium

Examiner: A 72-year-old woman on multiple medications including sotalol is found pulseless on the ward. The monitor shows polymorphic VT with a "twisting" QRS morphology. What is your approach?

Candidate response:

This is Torsades de Pointes (TdP) - a polymorphic ventricular tachycardia associated with prolonged QT interval. She is pulseless, so this requires immediate resuscitation.

Immediate management:

1. Call for help, initiate CPR
2. Defibrillation: Unsynchronized shock 200J biphasic
3. Adrenaline 1 mg IV after second shock per ALS algorithm

Specific treatment for Torsades de Pointes:

• Magnesium sulfate 2 g IV bolus over 1-2 minutes (even if serum magnesium is normal)
• This is the first-line specific treatment for TdP
• Magnesium stabilizes the cardiac membrane by inhibiting early afterdepolarizations

Examiner: ROSC is achieved. The QTc was 580 ms. Tell me about the causes and further management.

Candidate response:

Causes of prolonged QT and Torsades de Pointes:

Drug-induced (most common acquired cause):

• Antiarrhythmics: Sotalol (as in this patient), amiodarone, flecainide, procainamide
• Antibiotics: Macrolides, fluoroquinolones
• Antipsychotics: Haloperidol, quetiapine, olanzapine
• Antiemetics: Ondansetron, metoclopramide
• Antihistamines: Hydroxyzine
• Others: Methadone, TCAs

Electrolyte disturbances:

• Hypokalemia (prolongs QT, increases TdP risk)
• Hypomagnesemia
• Hypocalcemia

Congenital long QT syndrome

Other: Hypothyroidism, bradycardia, structural heart disease

Further management:

1. Stop all QT-prolonging medications (sotalol must be stopped)

2. Check and correct electrolytes:

   • Potassium: Target 4.0-4.5 mmol/L
   • Magnesium: Target greater than 1.0 mmol/L
   • Continue magnesium infusion 2-4 g over 24 hours

3. Maintain heart rate:

   • Bradycardia worsens QT prolongation
   • Target heart rate 100-110 bpm using:
     • Temporary pacing (transvenous or transcutaneous)
     • Isoprenaline infusion 1-10 mcg/min

4. ICU admission for continuous monitoring

5. Cardiology/EP consultation for consideration of:

   • ICD if recurrent episodes
   • Genetic testing if congenital LQTS suspected

Examiner: Why is magnesium effective even when serum levels are normal?

Candidate response:

Magnesium has direct membrane-stabilizing effects independent of serum levels:

1. Blocks L-type calcium channels: Reduces calcium influx during phase 2 of the cardiac action potential, shortening repolarization

2. Inhibits early afterdepolarizations (EADs): EADs are the trigger for TdP; magnesium suppresses the oscillatory calcium currents that cause EADs

3. Increases outward potassium current: Enhances IKs and IKr channels, accelerating repolarization

4. Stabilizes cell membranes: Reduces automaticity of triggered activity

These effects occur with supraphysiological magnesium concentrations achieved by IV bolus, even when baseline serum magnesium is within normal range. Serum magnesium also poorly reflects total body or myocardial magnesium content.

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Viva Scenarios (Additional)

Viva 3: Hypocalcemia in Massive Transfusion

Examiner: A 32-year-old male is receiving massive transfusion following a motor vehicle accident with liver laceration. He has received 12 units of PRBCs and 8 units of FFP in the past hour. The surgical team reports ongoing bleeding and poor clot formation. His ionized calcium is 0.78 mmol/L. Discuss your approach.

Candidate response:

This patient has severe hypocalcemia in the context of massive transfusion - this is a critical component of the "lethal diamond" (hypothermia, acidosis, coagulopathy, and hypocalcemia) that perpetuates hemorrhage.

Mechanism of hypocalcemia:

• Blood products contain citrate anticoagulant
• FFP has higher citrate content than PRBCs
• Citrate chelates ionized calcium forming calcium-citrate complexes
• With rapid transfusion, hepatic citrate metabolism is overwhelmed
• Hypocalcemia impairs coagulation (calcium is Factor IV in the clotting cascade)
• Also causes myocardial depression and hypotension, impairing resuscitation

Immediate management:

1. Calcium replacement:

   • Calcium chloride 10% 10 mL (1 g) IV via central line - preferred as provides 3x more elemental calcium than gluconate
   • Or Calcium gluconate 10% 30 mL (3 g) if only peripheral access
   • Can give as bolus in this emergency situation

2. Target ionized calcium greater than 1.1 mmol/L (minimum for adequate coagulation)

3. Prophylactic replacement protocol:

   • Give 1 g calcium gluconate (or 300 mg calcium chloride) for every 4 units of blood products
   • Alternatively, 1 g after every round of MTP

4. Monitoring:

   • Check iCa2+ every 15-30 minutes during active transfusion
   • Point-of-care blood gas analyzers provide rapid iCa2+ results

Examiner: What other electrolyte abnormalities would you anticipate and how would you manage them?

Candidate response:

Hyperkalemia:

• Stored blood has elevated potassium (up to 50 mmol/L in older units)
• Usually transient as potassium is redistributed intracellularly
• More significant in hypothermia (impairs cellular uptake) and AKI
• Monitor closely; treat if greater than 6.0 mmol/L with ECG changes
• Insulin-dextrose if needed; calcium already being given

Metabolic acidosis:

• Initially from hemorrhagic shock (lactic acidosis)
• Transfusion delivers citrate which is metabolized to bicarbonate (if liver functioning)
• Treat underlying shock with resuscitation
• Sodium bicarbonate rarely needed and may worsen ionized hypocalcemia

Post-resuscitation metabolic alkalosis:

• Once shock reversed, citrate metabolism generates bicarbonate
• Can cause rebound metabolic alkalosis

Hypomagnesemia:

• May occur with massive transfusion
• Check and replace if low
• Important as hypomagnesemia impairs calcium homeostasis

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Viva 4: Refractory Hypokalemia

Examiner: A 68-year-old woman has been in ICU for 5 days with severe community-acquired pneumonia. She has been receiving IV potassium replacement but her potassium remains at 2.8 mmol/L despite 120 mmol replacement in the past 24 hours. What is your approach?

Candidate response:

This is refractory hypokalemia - potassium not responding to aggressive replacement. The most common cause is concurrent hypomagnesemia.

Systematic approach:

1. Check magnesium level:

• Hypomagnesemia is the most common cause of refractory hypokalemia
• Mechanism: Magnesium acts as a "plug" in ROMK channels in the renal tubule; low magnesium leads to uncontrolled renal potassium wasting
• Potassium replacement will be ineffective until magnesium is corrected
• Target Mg2+ greater than 0.8 mmol/L

2. Identify ongoing losses:

Renal losses (urine K+ greater than 20 mmol/L):

• Diuretics (loop, thiazide)
• Vomiting/NG drainage (induces metabolic alkalosis and aldosterone release)
• Hyperaldosteronism
• Aminoglycosides, amphotericin B

GI losses (urine K+ below 20 mmol/L):

• Diarrhea
• Villous adenoma (rare)

Transcellular shift:

• Beta-2 agonists (nebulized salbutamol)
• Insulin infusion
• Metabolic alkalosis
• Catecholamine surge

3. Review medications:

• Diuretics - can these be stopped or reduced?
• Beta-agonists - minimize if possible
• Insulin infusion - ensure adequate potassium replacement in infusion

Examiner: Her magnesium is 0.55 mmol/L. How do you treat this?

Candidate response:

This is severe hypomagnesemia requiring aggressive IV replacement.

Treatment protocol:

1. Magnesium sulfate 8 mmol (2 g) IV over 1-2 hours initially
2. Follow with 40-60 mmol (10-15 g) over next 24 hours
3. Oral supplementation once tolerating (magnesium glycinate or citrate 400 mg BD)

Monitoring:

• Check magnesium 6-12 hours after loading
• Monitor for signs of hypermagnesemia if renal function impaired (loss of reflexes, respiratory depression)

Concurrent potassium replacement:

• Once magnesium corrected, potassium replacement will be more effective
• Continue IV KCl at appropriate rate (10-20 mmol/hour)
• Recheck potassium every 4-6 hours

Address underlying causes:

• Reduce loop diuretics if volume status allows
• Treat any ongoing GI losses
• Correct alkalosis if present

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Summary Tables

Electrolyte Emergency Quick Reference

Correction Rate Limits

IV Potassium Administration Guidelines

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