Diabetic ketoacidosis — formative SAQs

SAQ 1 — New-onset DKA in a seven-year-old (10 marks)

A 7-year-old boy weighing 22 kg presents with a two-week history of polyuria, polydipsia and weight loss, now vomiting and drowsy with deep sighing breathing. Blood glucose is 32 mmol/L, venous pH 7.08, bicarbonate 6 mmol/L, and blood beta-hydroxybutyrate 5.8 mmol/L. He is 6 per cent dehydrated but not shocked. (a) State the diagnosis and grade the severity. (b) Outline your fluid and insulin plan for the first hour. (c) Explain the potassium logic. (d) Name the complication you most fear and how you would recognise it. ^{[1] [3]}

Diagnosis and severity

This is diabetic ketoacidosis, meeting all three arms of the ISPAD triad: hyperglycaemia with a glucose of 32 mmol/L (above 11 mmol/L), acidosis with a venous pH of 7.08 and a bicarbonate of 6 mmol/L, and ketosis with a beta-hydroxybutyrate of 5.8 mmol/L. By the pH and bicarbonate this is severe DKA, because the pH is below 7.1 and the bicarbonate is below 5 to 10 mmol/L, and severe DKA in a young child mandates high-dependency or intensive-care nursing with hourly monitoring. ^[1]

Fluid and insulin plan for the first hour

He is dehydrated but not shocked, so he does not need a fluid bolus; a bolus is reserved for the shocked child at 10 mL/kg of isotonic saline. I would begin steady rehydration with isotonic saline, giving his maintenance plus an estimated deficit of around 5 to 7 per cent evenly over 48 hours, and I would not chase a precise clinical dehydration percentage because over-generous fluids are linked to cerebral oedema. Insulin is started only after fluids have begun, an hour or two in, as a continuous infusion of 0.05 to 0.1 units/kg/h, and never as a bolus. ^{[1] [2]}

The potassium logic

His serum potassium at presentation is likely to be normal or high despite a large total-body deficit, because the acidosis and the lack of insulin have driven potassium out of the cells and it has been lost in the urine. The moment insulin and fluids begin, potassium will move back into the cells and the serum level will fall, so I would add potassium to the fluids at 40 mmol/L once the level is below 5.5 mmol/L and he has passed urine, and monitor it hourly. Insulin should not be started in a child who is frankly hypokalaemic until the potassium is corrected. ^[1]

The feared complication

Cerebral oedema is the complication I most fear, because it is the leading cause of death in paediatric DKA and this young child with severe acidosis is high-risk. It typically appears four to twelve hours into treatment, often as the biochemistry improves, and I would recognise it clinically from a headache, a falling conscious level, irritability, incontinence, or a rising blood pressure with a slowing heart rate. I would treat immediately with hypertonic saline or mannitol, reduce the fluid rate, elevate the head of the bed, and call intensive care — without waiting for a scan, because outcome depends on the speed of recognition. ^{[3] [9]}