Clinical presentation

Incidental finding on blood biochemistry.

May be anticipated in the presence of oliguria associated with renal impairment.

Signs of cardiotoxicity:

• widened QRS complexes or tall, tented T-waves on ECG;

• dysrhythmias, such as ventricular tachycardia or fibrillation.

Definition

Blood potassium level >6.5 mmol/L.

Approach to the problem

• Is the biochemistry result true? How was the sample collected, and could it have been haemolysed? Repeat the sample as a matter of urgency.

• How many hours/days old is the infant? (Mild hyperkalaemia is not uncommon in extremely low birth weight (ELBW) infants in the first few days of life).

• Review history for antecedents of renal impairment (asphyxia and birth trauma).

• Is there a family history of renal problems? (e.g. polycystic kidneys).

• Look for contractures (suggestive of reduced fetal urine output causing oligohydramnios).

• Look for genital pigmentation (see Chapter 11) or ambiguity (see Chapters 8 and 10) suggestive of congenital adrenal hyperplasia.

Differential diagnosis

• Spurious (haemolysed blood sample).

• Renal impairment (including structural defects, e.g. urethral valves, dysplastic kidneys, and renal vascular accidents).

• Tissue damage (especially in immature infants with extensive bruising).

• Immaturity of renal potassium excreting capacity in ELBW infants.

• Acidosis (causing shift of potassium out of cells into extracellular fluid).

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