Emergency Medicine

140 Acid–Base, Electrolyte and Renal Emergencies

ELECTROLYTE DISORDERS

2 Causes include:

(i) Renal failure.

(ii) Iatrogenic magnesium administration i.v.

(iii) Rhabdomyolysis and tumour lysis syndrome.

3 Patients present with muscular weakness, respiratory depression, confusion,

ataxia and hypotension.

(i) Extreme magnesium toxicity >5.0 mmol/L may be associated

with bradycardia, respiratory depression, altered conscious level

and cardiac arrest.

4 Insert a large-bore i.v. cannula and send blood for FBC, U&Es, LFTs, magne-

sium and thyroid function.

5 ECG changes are similar to hyperkalaemia.

MANAGEMENT

1 Commence i.v. rehydration with normal saline at 500 mL/h.

2 Give 10% calcium chloride 10 mL i.v. for life-threatening arrhythmias and

severe magnesium toxicity.

3 Otherwise give a combination of normal saline i.v. and frusemide (furosem-

ide) 1 mg/kg i.v. to increase the renal excretion of magnesium, provided the

urine output is normal.

(i) Check calcium levels regularly to prevent hypocalcaemia, which

will worsen the symptoms of magnesium toxicity.

4 Refer the patient to the medical team or ICU for consideration of dialysis in

severe toxicit y wit h levels >5.0 mmol/L.

Hypomagnesaemia

DIAGNOSIS

1 Hypomagnesaemia occurs at a serum level of <0.6 mmol/L.

2 Causes include:

(i) Increased magnesium losses:

(a) gastrointestinal loss from vomiting, diarrhoea, pancreatitis

(b) acute tubular necrosis (ATN) or chronic renal failure

(c) drugs, e.g. alcohol, diuretics, gentamicin, digoxin.

(ii) Reduced magnesium intake in starvation, malnutrition, chronic

alcoholism.

(iii) Metabolic with low levels of calcium, phosphate and potassium.

(iv) Endocrine such as diabetic ketoacidosis (DKA), thyrotoxicosis,

hyperparathyroidism, hypothermia.

3 Clinical manifestations are non-specific and may mimic hypocalcaemia and

hypokalaemia. Look for tremor, paraesthesiae, tetany, altered mental state,

ataxia, nystagmus and seizures.