Paediatrics · Hard
This case is fictional and exists for study. It describes no real patient.
0 years · female
A 9-month-old female infant is brought to the emergency department by her parents with a 4-day history of profuse watery diarrhoea and vomiting. She has been unable to tolerate oral fluids for the last 24 hours and has had no wet nappies for 12 hours. Her parents report that she is unusually irritable when touched, but appears lethargic and somnolent when left alone. On examination, she has a sunken anterior fontanelle, dry mucous membranes, and a delayed capillary refill time of 4 seconds. Her skin feels unusually 'doughy' on palpation. She has peripherally cool extremities with weak peripheral pulses.
Vital signs
- HR
- 178 bpm
- BP
- 68/40 mmHg
- RR
- 52/min
- Temp
- 38.3 °C
- SpO₂
- 96%
Examination findings
- Prolonged capillary refill time of 4 seconds
- Doughy skin consistency on abdominal palpation
- Lethargic with alternating hyperirritability
- Sunken fontanelle and dry mucous membranes
- Weak peripheral pulses
Investigations
| Sodium | 158 mmol/L | reference: 135-145 |
| Potassium | 3.9 mmol/L | reference: 3.5-5.0 |
| Urea | 14.8 mmol/L | reference: 2.5-6.5 |
| Creatinine | 82 µmol/L | reference: 20-40 |
| Glucose | 4.2 mmol/L | reference: 3.5-5.5 |
Question 1 of 3
Which assessment best describes this infant's fluid and electrolyte status?
The infant presents with clinical shock (tachycardia, delayed CRT of 4s, hypotension, cool extremities) and hypernatraemic dehydration (serum sodium > 145 mmol/L, typical 'doughy' skin turgor, irritability alternating with lethargy). Option B is incorrect because the sodium is elevated (158 mmol/L) and hypotension indicates shock. Option C is incorrect because serum sodium is elevated, not reduced. Option A is incorrect because the clinical picture is driven by gastroenteritis hypovolaemia rather than primary cardiogenic shock.
Teaching point: Hypernatraemic dehydration classically presents with 'doughy' skin turgor, marked irritability, and intravascular volume preservation until dehydration becomes severe, leading to shock.
Question 2 of 3
What is the most appropriate initial management step for this patient?
According to UK paediatric guidelines (NICE CG84), any child with signs of clinical shock should receive an immediate intravenous bolus of 10 mL/kg 0.9% sodium chloride. Option D is incorrect because rapid correction of hypernatraemia with hypotonic fluids can cause fatal cerebral oedema. Option B is incorrect because enteral rehydration is contraindicated in the presence of shock. Option A is incorrect because glucose solutions are not appropriate for fluid resuscitation in hypovolaemic shock and can cause rapid osmotic fluid shifts.
Teaching point: In paediatric gastroenteritis with clinical shock, always prioritize acute intravascular resuscitation with a 10 mL/kg 0.9% sodium chloride fluid bolus regardless of the underlying serum sodium level.
Question 3 of 3
Following initial circulatory resuscitation and stabilization, what is the most appropriate strategy for correcting her remaining fluid deficit?
In hypernatraemic dehydration, brain cells adapt to high serum osmolality by producing idiogenic osmoles. Rapid reduction of serum sodium causes water to shift into brain cells, leading to cerebral oedema, convulsions, and brain herniation. Therefore, replacement of the fluid deficit must occur slowly over 48 hours (along with maintenance fluids), targeting a serum sodium reduction of no more than 0.5 mmol/L per hour (or 10-12 mmol/L in 24 hours). Options B and C involve overly rapid correction. Option D is incorrect because restriction below maintenance will worsen dehydration and renal impairment.
Teaching point: Fluid deficits in hypernatraemic dehydration must be replaced slowly over at least 48 hours to avoid rapid osmolality shifts and dangerous cerebral oedema.
Key learning points
- Clinical shock in children requires immediate resuscitation with a 10 mL/kg 0.9% sodium chloride bolus before fluid deficit calculations are addressed.
- Hypernatraemic dehydration is characterized by serum sodium > 145 mmol/L, doughy skin turgor, and prominent neurological signs (hyperirritability, somnolence).
- Hypernatraemic fluid deficits must be corrected gradually over at least 48 hours to prevent rapid serum sodium drops and cerebral oedema.
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