Sodium :The normal serum sodium level is 135–145 mmol/L.
Hypernatraemia:
This can be caused by hypovolaemia and dehydration as well as primary hyperaldosteronism, Cushing’s syndrome and excess salt intake. Patients present with lethargy, irritability, fever, nausea, vomiting and confusion. Management is with controlled hydration using 4% dextrose with 1/5 normal saline or 5% dextrose solution together with judicious diuretic therapy.
Hyponatraemia:
This can be caused by inappropriate secretion of antidiuretic hormone (SIADH), congestive cardiac failure, severe hepatic failure, Addison’s disease, aldosterone insufficiency, hypothyroidism, diuretic therapy, salt-losing nephropathy, renal tubular disorders and water retention. SIADH can be due to small cell lung cancer, central nervous system disorders such as meningitis and subarachnoid haemorrhage, lung disease such as asthma, pneu- monia and tuberculosis, and drug therapy with tricyclic antidepressants, carbamazepine and monoamine oxidase inhibitors. The phenomenon of pseudohyponatraemia occurs in hyperglycaemia, alcohol excess and hyperuricaemia. Significant hyponatraemia (serum sodium of < 125 mmol/L) presents with lethargy, confusion, convulsions and coma. Management of severe symptomatic hyponatraemia uses controlled infusion (1–3 mL/kg/h) of hypertonic saline (3% NaCl) with judicious diuretic therapy. Chronic, asymptomatic hyponatraemia can be well managed with fluid restriction to 1 L/day. Resistant hyponatraemia due to SIADH can also be treated with regular oral demeclocycline.
Potassium: The normal serum potassium level is 3.5–5.0 mmol/L.
Hyperkalaemia :
This can be caused by ACE inhibitor therapy, potassium-sparing diuretics, inadvertent potassium supplementation, acidosis, blood transfusion, haemolysis, severe renal failure, rhabdomyolysis and hypoaldosteronism. Patients present with severe muscular weakness, paralytic ileus, symptomatic bradycardia and heart block. Management of hyperkalaemia includes administration of 10 mL 10% calcium gluconate if there are electrocardiographic changes of hyperkalaemia (peaked T waves, small P waves and wide QRS complexes). Rapid reversal of potassium levels can be achieved by giving 50% glucose with insulin infusion, but the levels may rise again in a few hours. Concurrently administer oral or per rectum resonium 15–30 g and repeat administration as guided by subsequently measured serum potassium levels. Hyperkalaemia of severe renal failure needs haemodialysis.
Hypokalaemia :
Causes of hypokalaemia include loop diuretic therapy, primary hyperaldosteronism, Cushing’s syndrome, renal tubular disease, alkalosis and hyperthyroidism. Therapy with drugs such as verapamil, beta-agonists and amiodarone should be excluded. Hypokalaemia presents with muscle weakness or tetany. Significant hypokalaemia can lead to rhabdomyolysis. To manage hypokalaemia, usually oral supplementation alone will suffice. If the level is < 2.9 mmol/L, parenteral supplementation with KCl 10 mmol/L over an hour through a central venous line is indicated. The patient’s cardiac function should be monitored during this infusion. It should be repeated as guided by the subsequently performed serum potassium levels.
Calcium:
The normal serum calcium level is 2.2–2.5 mmol/L. The serum calcium level varies with the serum albumin level, and the correction can be made using the following formula:
Corrected serum Ca level =MEASURED SERUM CA LEVEL( mmol/L)+0.02 X (40 - SERUM ALBUMIN LEVEL)(g/dl)
Hypercalcaemia :
This can be caused by primary hyperparathyroidism, squamous cell carcinoma of the lung, cancer with bony metastases, multiple myeloma, sarcoidosis, vitamin D intoxication, milk-alkali syndrome and thiazide diuretics. Significant hypercalcaemia presents with anorexia, nausea, vomiting, constipation, polyuria, severe weakness, stupor and eventually coma. Steps in the management of hypercalcaemia include, first, hydration with adequate amounts of normal saline, together with loop diuretic therapy. More severe hypercalcaemia needs treatment with a bisphosphonate such as etidronate or pamidronate. Calcitonin injected subcutaneously or intravenously (200 units, 6-hourly) has a short-lived effect. Hypercalcaemia due to multiple myeloma, sarcoidosis or vitamin D toxicity can be treated also with glucocorticoids. Oral phosphate is useful when there is hypercalcaemia together with hypophosphataemia
Hypocalcaemia :
Causes of hypocalcaemia include hypoparathyroidism, vitamin D deficiency, osteomalacia, acute pancreatitis, chronic renal failure, malignancy with osteoblastic metastases, and pseudohypoparathyroidism. Patients present with circumoral and distal limb paraesthesias, painful muscle cramps, tetany and seizures. Patients may also have Chvostek’s sign and Trousseau’s sign.
Symptomatic hypocalcaemia and corrected serum levels of < 1.88 mmol/L should be treated with parenteral calcium in the form of 10% calcium gluconate.
