HYPOCALCAEMIA

    DEFINITION

    Abnormally low concentration of calcium in the blood (Total calcium
    < 2.20 mmol/L or 8.8 mg/dL).

    The ionized calcium is a more accurate reflection of calcium status,
    especially in patients with low serum albumin. The normal ionized
    calcium is from 1.12 to 1.23 mmol/L ( 2.24 to 2.46 meq/L, 4.48 to 4.92
    mg/dL).

    TOXIC CAUSES

    Ethylene glycol
    Fluorides and fluorosilicates
    Hydrofluoric acid (ingestion or skin contact)
    Oxalic acid and soluble oxalates
    Phosphate enemas
    Valproic acid

    NON-TOXIC CAUSES

    Hypoparathyroidism
    Malabsorption
    Pancreatitis
    Renal failure
    Vitamin D deficiency

    CLINICAL FEATURES

    Severe hypocalcaemia may appear within an hour of acute ingestion of
    hydrofluoric acid, fluorides, fluorosilicates or oxalic acid. 
    Paraesthesias, tetany, and convulsions are often present.  The
    electrocardiograph shows a widened or prolonged QT interval and large
    or peaked T waves.  Dysrhythmias and cardiac arrest may occur.

    DIFFERENTIAL DIAGNOSIS:

    Congenital QT prolongation syndrome
    Type Ia antiarrhythmic agents
    Tetanus
    Hyperventilation
    Strychnine
    Seizures

    RELEVANT INVESTIGATIONS

    Total and ionized serum calcium concentration
    Serum electrolytes: magnesium, phosphate, sodium and potassium
    concentration
    Renal function (urea, creatinine)
    Acidbase status (blood gases, serum bicarbonate)

    Electrocardiograph (QT interval and T wave morphology)
    Consider amylase, valproic acid, ethylene glycol levels in appropriate
    circumstances.

    TREATMENT

    After acute ingestion of hydrofluoric acid, fluorides, fluorosilicates
    or oxalic acid, calcium salts should be given orally or by gastric
    tube as soon as possible (50 mL of 10% calcium gluconate; 1 mL/kg in
    children).  Calcium acts as a chelating agent in the stomach. 
    Magnesium (e.g., magnesium hydroxide found in liquid antacid
    preparations) may also be helpful for fluoride ingestion. 

    Extensive skin contamination by hydrofluoric acid, fluorides,
    fluorosilicates or oxalic acid may lead to systemic toxicity and
    severe hypocalcaemia.

    In all patients with suspected or confirmed hypocalcaemia, perform
    continuous cardiac monitoring, and give intravenous  calcium 
     gluconate (10 to 15 mL over 3 to 5 minutes, 0.01 to 0.02 mL/kg in
    children). Further doses of calcium salts depend on serum calcium
    concentration and ECG.  The required dose of calcium salt may be from
    3 g to 20 g on the first day.  Calcium chloride may also be used, but
    contains approximately 3 times the amount of calcium per mL. 

    CLINICAL COURSE AND MONITORING

    Sudden cardiac arrest can occur - provide continuous
    electrocardiographic monitoring (QT interval, T waves). 
    Serum calcium and ionized calcium concentrations.
    Some of the causes of hypocalcaemia may also lead to severe
    hyperkalaemia - measure serum potassium and electrolytes frequently.

    AUTHOR(S)/REVIEWERS

    Author:        Dr V. Danel, Unité de Toxicologie Clinique, Grenoble,
                   France.

    Peer review:   Cardiff 9/96: V Afanasiev, M Burger, T Della Puppa,
                   L Fruchtengarten, K Olsen, J Szajewski.