Diabetic ketoacidosis — VBG interpretation and initial management

PLAB 2 & PRES 3 · endocrinology / emergency medicine · hard · 8 minutes

Candidate brief

You are an FY2 doctor/SHO in the Emergency Department. Hannah Lewis, 24, who has type 1 diabetes, presents with vomiting, abdominal pain, weakness and rapid breathing. Observations: Temperature 38.1°C. Heart rate 108 beats/min. Blood pressure 96/62 mmHg. Respiratory rate 28 breaths/min with deep breathing. SpO₂ 98% on air. GCS 15. Weight approximately 64 kg. Results: Capillary glucose 27.8 mmol/L. Blood ketones 5.8 mmol/L. Venous pH 7.12. pCO₂ 2.8 kPa. Bicarbonate 8 mmol/L. Sodium 132 mmol/L. Potassium 5.2 mmol/L. Chloride 99 mmol/L. Lactate 1.7 mmol/L. Interpret the results, assess the patient for possible causes and complications, explain the likely diagnosis and initiate an appropriate emergency management plan. Verbalise any examinations, investigations and treatments you would undertake.

What examiners look for

DKA is diagnosed when diabetes or glucose above 11 mmol/L, ketonaemia above 3 mmol/L or significant ketonuria, and venous pH below 7.3 and/or bicarbonate below 15 mmol/L are present. Venous blood gas testing is normally sufficient for assessing acidosis. Treatment aims to clear ketones and correct acidosis, not merely reduce glucose. Start 0.9% sodium chloride promptly and adjust the rate for blood pressure, hydration, cardiac disease and renal disease. Use fixed-rate intravenous insulin at 0.1 units/kg/hour. Continue the patient’s usual long-acting basal insulin. Potassium may initially be normal or high despite severe total-body potassium depletion and may fall rapidly after fluids and insulin. Add intravenous dextrose when glucose falls below 14 mmol/L so insulin can continue clearing ketones safely. Monitor glucose and ketones hourly and regularly reassess bicarbonate, potassium, electrolytes, fluid balance and urine output. Look for missed insulin, infection, pregnancy, myocardial infarction, pancreatitis, insulin-pump failure, alcohol/drugs and SGLT2-inhibitor-associated DKA. Routine bicarbonate and phosphate replacement are not recommended.

Guideline references

Practise this station

Role-play it with an AI patient and get feedback against the full marking scheme. Create a free account — 3 stations per month free.