Emergency Medicine

ELECTROLYTE DISORDERS

Acid–Base, Electrolyte and Renal Emergencies 135

MANAGEMENT

1 Replace potassium immediately in the following situations:
(i) Serum potassium <3.0 mmol/L.
(ii) Serum potassium 3.0–3.5 mmol/L in patients with chronic heart
failure or cardiac arrhythmias, particularly if on digoxin or
following myocardial infarction.

2 Give potassium 10–20 mmol/h i.v. under ECG control using a f luid infusion
device, but do not exceed 40 mmol/h.

3 Give magnesium sulphate 10 mmol (2.5 g) diluted in 100 mL normal saline
over 30–45 min in severe or intractable hypokalaemia, as magnesium
enhances potassium uptake and helps maintain intracellular potassium
levels.

4 Change to oral supplements or maintenance i.v. replacement when the serum
potassium is >3.5 mmol/L.

5 Refer the patient to the medical team as necessary for treatment of the under-
lying condition.

Sodium disorders

Sodium is the most common intravascular cation. It has a major inf luence on
serum osmolality and determines the volume of the extracellular f luid.

Hypernatraemia

DIAGNOSIS

1 Hypernatraemia is defined as a serum sodium level of >145–150 mmol/L.

2 Causes include:
(i) Decreased fluid intake with normal fluid loss:
(a) disordered thirst perception, e.g. hypothalamic lesion
(b) inability to communicate water needs, e.g. cerebrovascular
accident, infants, intubated patients.
(ii) Hypotonic fluid loss, with water loss in excess of salt loss:
(a) skin loss from excessive sweating in hot climates, dermal
burns
(b) gastrointestinal loss from diarrhoea or vomiting
(c) renal loss from impaired salt-concentrating ability, e.g.
diabetes insipidus, osmotic diuretic agents, hyperglycaemia,
hypercalcaemia, chronic renal disease.

Tip: consider hypokalaemia in any patient with an arrhythmia or in

✓ cardiac arrest.