Diabetic ketoacidosis with a potassium of 3.2 mmol/L

The unsafe element is starting insulin while the potassium is 3.2 mmol/L.

Insulin drives potassium into cells. In diabetic ketoacidosis the serum potassium is often normal or high despite total body depletion, because insulin deficiency and acidosis shift potassium out of cells. This patient's measured 3.2 mmol/L therefore represents a profound intracellular deficit. Starting insulin now would push the already low serum potassium down further and can cause fatal arrhythmias, respiratory muscle weakness and cardiac arrest.

The sequence must be reversed

1. Begin fluid resuscitation and potassium replacement first.
2. Withhold insulin until potassium is at least 3.3 mmol/L and rising.
3. Replace potassium aggressively and intravenously - the prescription of 20 mmol in the second litre is inadequate for a potassium of 3.2. Give 40 mmol/L of the infusion fluid (typically 40 mmol KCl per litre) and consider additional potassium by infusion pump, aiming for a rate of around 10–20 mmol/hour with cardiac monitoring.
4. Recheck potassium within 1 hour and after every subsequent change.
5. If the potassium falls further despite replacement, reduce the insulin rate rather than stopping potassium.

The other prescription elements - 1 litre of 0.9% saline in the first hour and insulin at approximately 0.1 units/kg/hour - are broadly appropriate for a 60 kg patient (6 units/hour) once the potassium allows them to start.

Fluids

• 0.9% sodium chloride 1 L over the first hour (already prescribed), then reassess pulse, blood pressure and urine output.
• Thereafter 0.9% sodium chloride 500 mL/hour for the next 3 hours, then 250–500 mL/hour depending on haemodynamics, sodium and urine output. Aim for a positive balance without causing overload.
• Once the glucose falls below 14 mmol/L, switch to 10% dextrose 500 mL over 4 hours (or equivalent) and continue saline as needed, so insulin can be continued safely.

Potassium

• Give 40 mmol KCl per litre of fluid while potassium is below 4.0, plus additional infusion if below 3.5.
• Target serum potassium 4.0–5.0 mmol/L. Check hourly initially, and monitor for peaked T waves or arrhythmia on ECG.

Insulin

• Start soluble insulin at 0.1 units/kg/hour = 6 units/hour once potassium is above 3.3 mmol/L.
• Do not give a bolus if fluids and infusion are started promptly.
• Reduce to 0.05 units/kg/hour (3 units/hour) when glucose falls below 14 mmol/L, keeping the infusion running until ketones clear and pH normalises.
• Continue long-acting basal insulin throughout - omitting it is a common cause of rebound ketosis.

Monitoring

• Hourly capillary glucose (aim for a fall of 3–5 mmol/L/hour, not faster), hourly capillary ketones, and venous blood gas with electrolytes 2-hourly at first.
• Continuous cardiac monitoring while potassium is abnormal, and strict fluid balance with hourly urine output via a catheter.
• Neurological observations hourly - headache, irritability, falling GCS or bradycardia suggest cerebral oedema.
• Watch the sodium trend: a rapidly rising corrected sodium suggests excessive free-water loss.

Complications to anticipate

• Hypokalaemia and arrhythmia; hypoglycaemia; fluid overload with pulmonary oedema, especially in a young patient with low urine output.
• Cerebral oedema - rare in adults but a leading cause of death in the young; treat with mannitol or hypertonic saline and urgent imaging if suspected.
• Aspiration, gastric stasis and venous thromboembolism; consider thromboprophylaxis once bleeding risk is assessed.
• Bicarbonate is not indicated - it worsens intracellular acidosis and hypokalaemia and is reserved for pH below 6.9.

Precipitants to find

• Infection - her temperature of 37.8 °C and vomiting justify urine, blood and chest cultures.
• Missed insulin, whether from illness, cost, eating disorder or psychological distress; involve the diabetes team before discharge.
• Pregnancy should be excluded in a young woman. Refer to the diabetes specialist nurse for sick-day education before she leaves.