Electrolyte Disorders: Calcium, Phosphorus, Magnesium

Electrolyte Disorders: Calcium, Phosphorus, and Magnesium

• Learning Objectives:
  • Describe the physiological role of calcium, phosphorus, and magnesium in the human body
  • Identify common causes of calcium, phosphorus, and magnesium disorders
  • Recognize these disorders based on clinical presentation
  • Explain the mechanisms of action of therapies used to treat hypercalcemia and hyperphosphatemia
  • Design a patient care plan and treatment regimen for calcium, phosphorus, and magnesium disorders
• Electrolyte Abnormalities: Treatment Indications and Goals
  • Indications: Dependent on severity (how far the electrolyte level is from normal) and the speed of development (acute vs. chronic)
    • Acute: ≤ 48 hours
    • Chronic: > 48 hours
  • Goals:
    • Reverse signs and symptoms
    • Identify and correct/manage the underlying cause
    • Restore electrolytes to normal values

Calcium

• Calcium Homeostasis: Disorders related to calcium content in extracellular fluid (ECF)
  • Ionized Calcium: The physiologically active form of calcium. ~50% of calcium in ECF is bound to protein, primarily albumin.
• Corrected Calcium: -Formula: Measured Calcium + (0.8 x [4 g/dL - Measured Albumin])

Hypercalcemia

• Definition: Serum calcium > 10.5 mg/dL (2.63 mmol/L) or ionized calcium > 5.6 mg/dL
• Severity Scale: Categorized based on total and ionized calcium levels
  • Mild: 10.5-11.9 mg/dL (5.6-8 mg/dL ionized)
  • Moderate: 12-13.9 mg/dL (8-10 mg/dL ionized)
  • Severe: 14-16 mg/dL (10-12 mg/dL ionized)

Hypercalcemia: Treatment Algorithm

• Symptomatic (Ca > 12 mg/dL):

  • eGFR > 30: IV saline rehydration, loop diuretics, calcitonin
  • **eGFR < 30 or HF with EF <25%: ** Calcitonin, Bisphosphonates, Denosumab, Corticosteroids - treat underlying malignancy when suspected

• Asymptomatic (Ca < 12 mg/dL): Observe, Correct volume depletion, stop offending medications

IV Saline Rehydration

• Mechanism: Volume expansion with normal saline (NS) to increase natriuresis (sodium excretion) and urinary calcium excretion
• Treatment: Bolus of 1-2 L of NS, followed by maintenance infusion of 250-300 mL/hr
• Duration: Until fluid resuscitation is complete and serum calcium approaches the upper limit of normal, or response is seen in 24-48 hrs.
• Place in Therapy: First-line for symptomatic hypercalcemia (serum calcium >12 mg/dL)

Loop Diuretics

• Mechanism: Block calcium and sodium reabsorption in the loop of Henle, augmenting the calciuric effect of saline.
• Use: In combination with IV isotonic fluids (NEVER as monotherapy) for patients who have normal to moderately impaired kidney function and serum calcium is >12 mg/dL or symptomatic; to minimize volume overload from high doses of IV fluids.
• Dosing: Monitor IV every 1-4 hours of furosemide or equivalent loop diuretic dose.

Calcitonin

• Mechanism: Inhibits osteoclast activity, reduces renal tubular reabsorption of calcium (and thus promotes calciuresis).
• Use: First-line in cases with contraindications to IV saline rehydration (e.g., heart failure with EF < 25% or eGFR<30) or for symptomatic or moderate-severe hypercalcemia (Ca > 12 mg/dL.
• Dosage: 4 units/kg SQ or IM every 12 hours

Bisphosphonates (IV)

• Mechanism: Block bone resorption and inhibit osteoclasts, lowering blood calcium levels.
• Use: First-line for long-term, chronic treatment of moderate-severe hypercalcemia of malignancy
• When to use: In severe cases or when other therapies aren't working, specifically when hypercalcemia of malignancy is suspected.
• Common types and dosages:
  • Pamidronate: 30-90 mg IV over 2-24 hours
  • Zoledronic Acid: 4-8 mg IV over 15 minutes (Do not give if CrCL <30)

Denosumab

• Mechanism: Monoclonal antibody that inhibits RANKL, preventing osteoclast formation.
• Use: Chronic treatment in patients with hypercalcemia of malignancy when IV bisphosphonate therapy has failed or is not an option due to severe renal dysfunction (serum calcium >12.5 mg/dL after >7 days of therapy).
• Adverse Effects: Osteonecrosis of the jaw, severe symptomatic hypocalcemia (CKD patients).

Corticosteroids

• Mechanism: Reduce gastrointestinal calcium absorption by inhibiting vitamin D activation
• Use: In hypercalcemia associated with malignancies that overproduce calcitriol (multiple myeloma, leukemia, lymphoma).
• Dosage Prednisone 40-60mg PO or equivalent, for 3-5 days, followed by maintenance dose of 10-30 mg/day

Hypocalcemia

• Definition: Serum calcium < 8.5 mg/dL (2.1 mmol/L) or ionized calcium < 4.4 mg/dL (1.1 mmol/L)

Hypocalcemia: Treatment Algorithm

• Symptomatic (acute): IV calcium chloride or gluconate over 10 minutes; IV bolus or initial 1 g/hr infusion
• Asymptomatic (acute): IV calcium gluconate bolus (1 g/hr)
• Asymptomatic (chronic): Oral calcium supplementation (1-3 g/day) or vitamin D, especially when serum 25(OH) vitamin D levels are very low.

Hypophosphatemia

• Definition: Serum phosphorus <2.5 mg/dL
• Severity Scale: Categorized based on serum phosphorus.
  • Mild: 2-2.4mg/dL
  • Moderate: 1-2 mg/dL
  • Severe: <1 mg/dL

Hypophosphatemia: Treatment

• Mild-Moderate (1-2 mg/dL): Oral phosphate salts (1.5-2 g/day), divided doses.
• Severe (<1 mg/dL): IV phosphate repletion (sodium or potassium phosphate 15-30 mmol/ in 250 mL of D5W or NS over 3 hours).

Phosphorus Replacement Therapy

• Oral Therapy: Various products offering different amounts of phosphorus, tailored to serum potassium (K) levels.
• IV Therapy: IV administration when oral isn't feasible or when severe symptoms are present.

Magnesium

• Magnesium distribution: Predominantly in bone (67%) and muscle (20%)
• Normal Magnesium levels: 1.7-2.4 mg/dL (1.4-1.8 mEq/L)

Hypermagnesemia

• Definition: Serum Magnesium >2.4 mg/dL (2 mEq/L)

Hypermagnesemia: Treatment

• Reduce Magnesium intake
• IV Elemental Calcium - 100-200 mg (Calcium Gluconate 1-2g IV)
• Enhance Magnesium elimination
  • Normal renal function (CKD 1-3): Furosemide (40mg IV) or equivalent diuretic + isotonic fluids
  • ESRD (CKD 4-5 or end stage renal disease): Dialysis

Hypomagnesemia

• Definition: Serum Magnesium < 1.7 mg/dL (1.4 mEq/L)

Hypomagnesemia: Treatment

• Mild-Moderate (1.2-1.7 mg/dL): PO magnesium supplementation (400-800 mg/day magnesium oxide).
• Severe (≤ 1.2 mg/dL) or symptomatic: IV magnesium sulfate (8-12 g over 24 hrs divided doses) or (4-6 g divided doses over 3-5 days).

Common Calcium, Phosphorus, and Magnesium Salts

• Tables provided in the slides summarize different products and their elemental contents.

Take Home Points

• Electrolyte treatment depends on the severity and underlying cause.
• "Hyper-" electrolyte treatment aims to eliminate or redistribute.
• "Hypo-" electrolyte treatment often involves supplementation, IV or PO route depending on the acuity and severity.

This quiz focuses on the significance of calcium, phosphorus, and magnesium in human physiology. It covers common disorders related to these electrolytes, their clinical presentations, and treatment strategies. Additionally, it addresses the creation of patient care plans involving these essential minerals.