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.