Diabetic ketoacidosis — VBG interpretation and initial management

PLAB 2 & PRES 3 · emergency · hard · 8 minutes

Candidate brief

You are an FY2 doctor/SHO in the Emergency Department. Ms Sophie Byrne, 26, who has type 1 diabetes, presents with vomiting, abdominal pain and rapid breathing. Assess her rapidly, interpret the available venous blood gas and biochemical results, explain the likely diagnosis and initiate an appropriate emergency management plan. Verbalise any immediate actions, investigations and escalation you would undertake.

What examiners look for

This VBG demonstrates a primary metabolic acidosis: pH 7.16 confirms acidaemia. Bicarbonate 10 mmol/L is low. pCO₂ 3.2 kPa is reduced through respiratory compensation. The anion gap is: 132 − (98 + 10) = 24 mmol/L This is a raised-anion-gap metabolic acidosis. DKA is confirmed by known diabetes or glucose above 11 mmol/L, ketones above 3 mmol/L and venous pH below 7.3 or bicarbonate below 15 mmol/L. An initially normal or raised serum potassium does not mean total-body potassium is adequate. Potassium can fall rapidly after fluids and insulin, so frequent monitoring and protocol-based replacement are essential. Start 0.9% sodium chloride and fixed-rate IV insulin according to the adult DKA pathway. For a 60 kg patient, 0.1 units/kg/hour corresponds to 6 units/hour. Continue the patient’s usual long-acting basal insulin. Do not stop basal insulin simply because the patient is vomiting or not eating. When glucose falls below 14 mmol/L, add IV glucose so insulin can continue suppressing ketone production without causing hypoglycaemia. Assess treatment using ketone clearance, pH, bicarbonate, glucose, potassium, observations and fluid balance—not glucose alone. Search for and treat the trigger, commonly infection, insulin omission, pump failure, myocardial infarction, pancreatitis, pregnancy or medicines such as SGLT2 inhibitors. Routine bicarbonate and phosphate replacement are not recommended.

Guideline references

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