Paeds Cases · endocrinology-diabetes-and-growth
SIADH and disorders of water balance — OSCE
OSCE communication and clinical reasoning station explaining hospital-acquired hyponatraemia and SIADH, the fluid-restriction plan, and the prevention of overcorrection to the parents of an unwell child.
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MRCPCH ClinicalRACP DCE
Prompt
You have 8 minutes with the mother of a 3-year-old boy admitted with pneumonia. On his second day on intravenous fluids he became drowsy and had a seizure, and his blood test showed a low sodium (121 mmol/L). He was treated with a hypertonic saline drip in the high-dependency unit and has recovered. The team has diagnosed SIADH triggered by the pneumonia. Explain what happened, why the sodium fell, the treatment and monitoring plan, and how it will be prevented, and agree a way forward.
Station brief (candidate)
- Explain in plain language what happened: the level of salt in his blood dropped too low, which made his brain swell a little and caused the seizure; the team gave a special strong salt drip to lift it safely, and he has recovered. [7]
- Explain why the salt fell: his pneumonia made his body hold on to extra water (through a hormone called ADH), and the drip fluid he was on added more water, so the salt in his blood became too diluted. [8]
- Name the diagnosis simply: this is called SIADH — the body holding on to too much water because of the illness. It is common in unwell children and usually gets better as the illness gets better. [12]
- Explain the plan: we now limit how much fluid he takes in for a short while (fluid restriction) so his body can get rid of the extra water, we treat the pneumonia, and we check his salt level with regular blood tests. [12]
- Explain the safety point about correcting slowly: we bring the salt back up gently, not too fast, because raising it too quickly can harm the brain; this is why we check the blood so often. [10]
- Reassure and safety-net: the seizure was caused by the low salt and is not epilepsy, the risk falls as the salt normalises, and in future he should be given the safer (isotonic) drip fluid and have his salt watched if he ever needs a drip again. [6]
References5ShowHide
- [6]Moritz ML; Ayus JC Maintenance Intravenous Fluids in Acutely Ill Patients. N Engl J Med, 2015.PMID 26422725
- [7]Moritz ML; Ayus JC New aspects in the pathogenesis, prevention, and treatment of hyponatremic encephalopathy in children. Pediatr Nephrol, 2010.PMID 19894066
- [8]Driano JE; Lteif AN; Creo AL Vasopressin-Dependent Disorders: What Is New in Children? Pediatrics, 2021.PMID 33795481
- [10]Sterns RH Adverse Consequences of Overly-Rapid Correction of Hyponatremia. Front Horm Res, 2019.PMID 32097948
- [12]Hoorn EJ; Zietse R Diagnosis and Treatment of Hyponatremia: Compilation of the Guidelines. J Am Soc Nephrol, 2017.PMID 28174217