Hypocalcemia

Pathophysiology

• In the nervous system, low serum calcium levels cause increased membrane permeability to sodium and hence, neuronal excitability. This effect is counteracted by potassium and magnesium.
• In the heart, low ionized calcium reduces the strength of myocardial contraction.

Diagnosis and Evaluation

• As with other electrolytes, the severity of clinical manifestations are magnified with rapidity on onset.
• Clinical manifestations are both neurological and cardiovascular. Neurological features range from paresthesia and weakness to tetany, altered mental status and seizures. Cardiac features may include congestive heart failure, hypotension and dysrhythmias, hypercalcemia.
• Important physical examination findings suggestive of hypocalcemia include a anterior neck scar from thyroid surgery, hypokalemia, hyperactive deep tendon reflexes and a positive Trousseau sign (carpal spasm resulting from inflation of a blood pressure cuff.
• Consider causes of hypocalcemia that may require other critical actions:

  Causes	Actions
  Magnesium depletion	STAT IV magnesium replacement
  Renal dysfunction	Consider dialysis
  Acute pancreatitis/sepsis	Aggressive treatment of underlying process
  Rhabdomyolysis	Saline diuresis, sodium bicarbonate
  Fat embolism	Mechanical ventilation, consider heparin
  Exogenous drug administration	Discontinue agent
  - phosphate containing agents - loop diuretics - corticosteroids - theophylline - heparin - sodium nitroprusside - cimetidine - phenytoin

• Look for signs of focality on neurological examination and consider other causes of neurological deficits.

Laboratory/Studies

• Measure STAT electrolytes, including Mg, PO4 and albumin.
• Although hypoalbuminemia will decrease the measured total calcium, the clinically relevant ionized calcium will not be affected.
• A STAT EKG is indicated to rule out prolonged QT interval (normal width T wave with prolonged ST segment) as this predisposes the patient to lethal dysrhythmia
• Consider head CT to rule out intracranial pathology
• Electrolytes should be measured every 1-2 h during correction.

ED Management

• Beware of over-aggressive ventilation in the mechanically ventilated patient; respiratory alkalosis causes a decrease in the ionized fraction of calcium, with no change in the serum level (each 0.1 rise in pH lowers ionized Ca by about 5%)
• For symptomatic patients or those with a prolonged QT interval, use 10% calcium gluconate IV (20 ml over 10 min) followed by infusion of 60 ml in 500 ml of 5% dextrose in water (D5W) at 1 mg/kg/h.
• In cardiac arrest, use 10% calcium chloride (1 g) IV push. This dose may be repeated.