Acid-base disorders in children — OSCE

Candidate brief

You are the paediatric registrar. The patient is 8 and was admitted overnight in diabetic ketoacidosis, his first presentation of type 1 diabetes. He is now on the DKA protocol with fluids and an insulin infusion, his pH is improving and his breathing has settled. His parents are anxious and have asked why his breathing was so deep, why a blood test was being done so often, and whether a medicine to neutralise the acid should be given. Explain clearly what the blood gas showed and what it means, what the treatment is doing, why no bicarbonate is being given, and agree a safety-net and a forward plan for diabetes education. [1]

Marking domains

Clinical knowledge and accuracy (3). Explains that the blood gas showed a metabolic acidosis — the blood had become too acid because, without insulin, the body broke down fat and produced acidic ketones, and that the deep sighing breathing was the body's own attempt to breathe out the acid as carbon dioxide. Explains that the treatment is fluid to correct the dehydration and insulin to switch off the ketone production, so the acid clears as the cause is treated, and that the gas is checked often to confirm the acid is falling. Correctly states that bicarbonate is not given because it does not help and can cause harm, reserved only for the rare child with very severe acid. [5][10]

Communication and plain language (3). Avoids jargon or defines it; uses an analogy (the body became too acid, like vinegar, and the breathing was blowing off the fumes); gives a concrete reassurance (the pH is rising, the breathing has settled, he is recovering). Paces the information, pauses to check understanding, and invites questions rather than overwhelming the parents with numbers. Frames the diagnosis of type 1 diabetes as a new condition the family will learn to manage, not a failure of anything they did. [1][6]

Management plan and safety-net (3). Lays out the immediate plan: continued fluids and insulin until the ketones clear and he can eat, then a switch to a tailored insulin regimen the family will learn. Explains the sick-day rules for the future: never stop the insulin during illness, check the ketones when unwell, keep up the fluids, and seek help early for vomiting, drowsiness or rapid breathing. Gives a clear safety-net: the warning signs of recurrence are fast deep breathing, drowsiness, vomiting and abdominal pain, and any of these means an urgent review. [5][6]

Empathy and partnership (1). Acknowledges the parents' shock at a new diagnosis presenting as an emergency, reassures them that the recovery is proceeding well, and frames the diabetes education as a partnership the family will own over the coming days and weeks. [5]

Examiner notes

Strong candidates explain the acid-base disturbance in plain terms (the body became too acid from ketones, the breathing was compensation, the treatment removes the cause), give a concrete reason why bicarbonate is not used without over-medicalising it, and pair the explanation of the acute episode with a forward plan for diabetes education and sick-day rules. Weak candidates flood the parents with numbers, fail to address the anxiety, or offer bicarbonate as a quick fix. The interpretation of the gas as a metabolic acidosis with appropriate compensation, and the principle of treating the cause rather than the number, are the discriminators at the high end. [1][3]