Emergency Medicine

ELECTROLYTE DISORDERS

Acid–Base, Electrolyte and Renal Emergencies 139

Hypocalcaemia

DIAGNOSIS

1 Hypocalcaemia is defined by a serum calcium level of <2.1 mmol/L after
correction for albumin.

2 Causes include:
(i) Chronic renal failure, acute pancreatitis.
(ii) Rhabdomyolysis, tumour lysis syndrome, whole blood
transfusion and toxic shock syndrome.
(iii) Primary respiratory alkalosis (hyperventilation).
(iv) Calcium-channel blocker overdose.

3 Patients present with paraesthesiae of the extremities and face, muscle
cramps, carpopedal spasm, stridor, tetany, seizures and cardiac failure.

4 Look for hyper-ref lexia and a positive Chvostek’s or Trousseau’s sign:
(i) Chvostek’s sign: facial twitching from percussing the facial nerve
in front of the ear.
(ii) Trousseau’s sign: carpal spasm after 3 min of inflation of a BP
cuff above systolic pressure.

5 Insert a large-bore i.v. cannula and send blood for FBC, U&Es, LFTs, creatine
kinase (CK), magnesium and lipase.

6 Perform an ECG and look for:
(i) QT interval prolongation, T wave inversion.
(ii) AV block, torsades de pointes (cardiac arrest may ensue).

MANAGEMENT

1 Commence rehydration wit h 0.9% norma l sa line i.v. at 250 mL/h.

2 Look for and treat the underlying cause.

3 Give calcium i.v. in symptomatic patients:
(i) 10% calcium chloride 10–40 mL i.v.
(ii) discuss further elemental calcium infusion with the medical
team or intensive care unit (ICU) admitting team.

4 G i ve c a lc iu m by or a l c a lc iu m s upplement s , or v it a m i n D -r ic h m i l k i n a s y mp -
tomatic patients.

Magnesium disorders

Magnesium is the second most abundant intracellular cation and essential for
stabilizing excitable cellular membranes and facilitating the movement of
calcium, potassium and sodium into and out of cells.

Hypermagnesaemia

DIAGNOSIS

1 Hypermagnesaemia occurs at a serum level of >1.1 mmol/L.