Rosen & Barkin's 5-Minute Emergency Medicine Consult (376 page)

• Hypocalcemia is defined as a total plasma calcium level <8.7 mg/dL:
  
  • Ionized calcium may be normal and, therefore, have no clinical manifestations.
    
• Normal total serum calcium concentrations are 8.7–10.5 mg/dL.
  

• Incidence in the general population is 0.6%.
  
• Mechanism:
  
  • From either increased loss of calcium from the circulation or decreased entry into the circulation
    
  • Intravascular calcium circulates in 3 forms:
    
    • Bound to proteins (mainly albumin): 45–50%
      
    • Bound to complexing ions (citrate, phosphate, carbonate): 5–10%
      
    • Ionized (free) calcium (physiologically active form): 45–50%
      
  • Serum levels of calcium are primarily controlled by 3 hormones:
    
    • Parathyroid hormone (PTH)
      
    • Decrease in calcium levels leads to an increase in PTH secretion (increasing bone resorption, renal absorption, intestinal absorption, urinary phosphate excretion).
      
  • Vitamin D (1,25-dihydroxyvitamin D):
    
    • Decrease in calcium level activates vitamin D (increasing bone resorption and intestinal absorption).
      
  • Calcitonin:
    
    • Causes a direct inhibition of bone resorption with increased calcium levels
      
• Hypoalbuminemia—the most common cause:
  
  • Each 1 g/dL decrease in serum albumin decreases protein-bound serum calcium by 0.8 mg/dL.
    
  • Ionized (free) calcium levels do not change.
    

• Children have higher values of normal calcium (9.2–11 mg/dL).
  
• Neonatal hypocalcemia: Total serum calcium concentrations <7.5 mg/dL or serum-ionized calcium levels <4 mg/dL
  
• Symptoms of hypocalcemia in infancy:
  
  • Hyperactivity, jitteriness
    
  • Tachypnea
    
  • Apneic spells with cyanosis
    
  • Vomiting
    

DIAGNOSIS

• Occur when ionized calcium <3.2 mg/dL
  
• Dependent upon absolute calcium concentration and rate at which it falls
  
• Neuromuscular:
  
  • Paresthesias
    
  • Hyperreflexia
    
  • Muscle spasm
    
  • Tetany:
    
    • Neuromuscular irritability
      
    • Uncommon unless ionized calcium <4.3 mg/dL
      
  • Latent tetany
    
  • Chvostek sign (finger taps of parotid gland over the facial nerve causes facial muscle spasm)
    
  • Trousseau signs (an inflated blood pressure cuff over the arm causes carpopedal spasm)
    
  • Laryngeal stridor
    
  • Seizures
    
  • Choreoathetosis
    
• Cardiovascular:
  
  • Dysrhythmias:
    
    • Torsades de pointes
      
    • Heart block
      
  • Hypotension
    
  • Impaired contractility (heart failure)
    
  • ECG changes:
    
    • Bradycardia
      
    • QT and ST prolongation
      
    • T-wave abnormalities
      
• Psychiatric:
  
  • Irritability/anxiety
    
  • Psychosis
    
  • Depression
    
  • Confusion
    
  • Delusions
    
  • Chorea
    
  • Parkinsonisms
    
• Ocular:
  
  • Papilledema
    
  • Cataracts
    
  • May occur in patients with acute onset hypocalcemia
    

Serum-ionized calcium level confirms the diagnosis

• Arterial blood gas:
  
  • Change from normal pH of 0.1 U equals a reciprocal change in ionized calcium of ∼1.7 mg/dL.
    
• Serum albumin
  
• Electrolytes, BUN/creatinine, glucose
  
• Magnesium
  
• Phosphate:
  
  • Increase in phosphate associated with hypoparathyroidism
    
  • Decrease in phosphate associated with vitamin D deficiency
    
• PTH:
  
  • Very high levels of PTH associated with pseudohypoparathyroidism
    
  • High levels of PTH associated with vitamin D deficiency
    
  • Low levels of PTH associated with hypoparathyroidism
    
• Serum calcidiol or calcitriol
  

ECG:

• Prolonged QT interval
  
• Heart block
  

• Impaired PTH action or secretion:
  
  • Parathyroid or thyroid surgery or radical neck surgery and/or irradiation for head and neck cancer
    
  • Autoimmune disease (typically presents in childhood)
    
  • Congenital hypoparathyroidism
    
  • Neonatal secondary to maternal hyperparathyroidism
    
  • Pseudohypoparathyroidism (resistance to PTH)
    
  • Infiltrative (amyloidosis, sarcoidosis, metastases, iron overload)
    
  • HIV infection
    
• Impaired vitamin D synthesis or action:
  
  • Nutritional malabsorption or poor intake
    
  • Renal disease
    
  • Pronounced hypophosphatemia
    
• Sepsis or severe burns:
  
  • Impaired secretion of PTH and calcitriol
    
  • End-organ resistance to the action of PTH
    
• Calcium complex formation or sequestration:
  
  • Hyperphosphatemia
    
  • Ethylene glycol, ethylenediaminetetraacetic acid (EDTA), citrate (from transfusion)
    
  • Pancreatitis, rhabdomyolysis
    
  • Alkalosis (i.e., hyperventilation)
    
• Hypomagnesemia:
  
  • Causes end-organ PTH resistance
    
  • Decreased PTH secretion
    
  • Seen in chronic and/or critical illness
    
  • Must give magnesium to correct hypocalcemia
    
• Medications:
  
  • Mithramycin, plicamycin, phosphate, calcitonin, bisphosphonates
    
  • Phenobarbital, phenytoin
    
  • Cisplatin
    
  • Cadmium, colchicine
    
  • Fluoride, citrate, PPI
    
• Malignancies:
  
  • Prostate cancer
    
  • Breast cancer
    
  • Lung cancer
    
  • Chondrosarcoma
    
• “Hungry bone syndrome”:
  
  • After parathyroid removal
    
  • Rapid accretion of calcium as bone is remineralized
    

TREATMENT

ABCs:

• Establish IV catheter access.
  
• Cardiac monitor
  

• Acute management:
  
  • Treat symptomatic hypocalcemia as a medical emergency with parenteral calcium administration.
    
  • Calcium IV bolus:
    
    • Calcium gluconate 1–2 g in 50 mL of 5% dextrose
      
    • Infuse over 20 min
      
    • Faster IV rates can cause cardiac dysrhythmias
      
    • Calcium salts are irritating to veins.
      
    • IM calcium gluceptate or calcium gluconate if IV access not available
      
    • Bolus dose increases ionized calcium for only 1–2 hr, therefore, must be followed by an infusion
      
  • Calcium infusion:
    
    • Calcium infusion rate: 0.5–1.5 mg/kg/hr
      
    • Do not mix with bicarbonate or phosphate or precipitation of salts may form.
      
    • Administer cautiously in patients taking digitalis—may initiate and exacerbate digitalis toxicity
      
  • Response to therapy:
    
    • Individual responses vary.
      
    • Monitor calcium concentrations q1–4h during therapy.
      
    • Titrate treatment to symptoms or ECG changes.
      
    • Consider hypomagnesemia if the patient fails to respond to calcium therapy—correct hypomagnesemia with Mg 2 g IVPB 10% solution over 10 min
      
    • In the setting of acidosis, correct calcium 1st; alkalosis will further reduce ionized calcium.
      
    • Side effects of IV calcium include: Nausea, vomiting, hypotension, and dysrhythmias
      
• Chronic management:
  
  • Oral calcium supplementation
    
  • 1.5–2 g/day of Calcium in div. doses. May need up to 4 g/day in patients with malabsorption.
    
  • Vitamin D:
    
    • Enhances intestinal absorption
      
    • Initiate with calcium supplementation—alone not sufficient to restore calcium levels.
      
    • 600 IU for ages 19–50 yr
      
    • 600 IU for ages 51–70 yr
      
    • 800 IU for ages 71 and older
      
    • Multivitamins contain variable amounts of vitamin D
      
  • Vitamin D preparations:
    
    • Ergocalciferol: 125 μg/day
      
    • Dihydrotachysterol: 100–400 μg/day
      
    • Calcifediol: 50–200 μg/day
      
    • Calcitriol: 0.25–0.5 μg/day: Rapid onset (preferred). Most active metabolite of vitamin D
      

Calcitriol requirements may double or triple toward the end of pregnancy.

• IV calcium:
  
  • Calcium chloride: 1 g in 10 mL (1 g = 360 mg [13.6 mEq] elemental calcium)
    
  • Calcium gluceptate (IV/IM): 1 g in 5 mL (1 g = 90 mg [4.5 mEq] elemental calcium)
    
  • Calcium gluconate: 1 g in 10 mL (1 g = 90 mg [4.5 mEq] elemental calcium)
    
• Oral calcium:
  
  • Calcium carbonate: 350–1,500 mg tablets (1 g = 400 mg)
    
  • Calcium citrate: 950 mg tablets (1 g = 211 mg elemental calcium)
    
  • Calcium glubionate: 18 g/5 mL of syrup (1 g = 65 mg elemental calcium)
    
  • Calcium gluconate: 500—1,000 mg tablets (1 g = 90 mg elemental calcium)
    
  • Calcium lactate: 350–1,000 mg tablets (1 g = 130 mg elemental calcium)
    

• Initial calcium bolus with 10% calcium gluconate should be 9–18 mg of elemental calcium/kg or 1–2 mL/kg not to exceed 5 mL in premature infants or 10 mL in term infants.
  
• Calcitriol dose in children ranges from 0.1–3 μg/day.
  
• MISCELLANEOUS:
  
  • Calcium content of common foods:
    
    • Milk or yogurt, 8 oz = 300 mg
      
    • Cheddar cheese, 1 oz = 200 mg
      
    • Calcium-fortified cereal, 1 cup = 300 mg
      
    • Calcium-fortified orange juice, 1 cup = 270 mg
      
    • Shrimp, 3 oz = 50 mg
      
    • Peanuts = 130 mg
      
    • Orange = 50 mg
      

FOLLOW-UP