Case Studies

Case 1: A vomiting baby

A 5-week-old baby has been vomiting for the last 48 hours. Initially he was keeping some feeds down but now he is vomiting after every feed. He was breast-fed initially but for the last week has been given formula milk via a bottle because his mother, who is only 17, developed a breast abscess and decided to stop breast-feeding.

• (a) You are worried about this baby, who seems quite ill. What further information do you need from the history?

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  You need to establish the cause of the vomiting. Is it associated with diarrhoea, which would make gastroenteritis more likely, or is it associated with constipation, which may suggest a bowel obstruction? Is the vomiting bile stained, which suggests a serious bowel obstruction, or is it just curdled milk? Is the vomiting minor posseting, suggestive of gastro-oesophageal reflux, or is it projectile, as occurs in pyloric stenosis? Finally, the baby has recently changed feeds so you might want to ask how this young mother is making up the feeds—non-sterile water may cause gastroenteritis, or over-concentrated feeds may cause electrolyte imbalance.

• (b) Do you think he is dehydrated? If so, to what degree?

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  This child shows features of moderate dehydration (5–10%), with a sunken fontanelle, dry lips, tachycardia and slightly long capillary refill time, but without signs of shock. The dry nappy suggests he may not be passing urine, but this needs to be established from the history.

• (c) His mother is carrying her child health record (red book). How can you establish exactly the degree of dehydration?

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  Look for a recent weight. In fact this baby weighed 3.3 kg a week ago. He has therefore lost 300 g. If we assume all this weight loss is due to fluid loss, this represents 9% dehydration.

• (d) Which of the following is the most likely diagnosis? (1) Acute renal failure; (2) Inborn error of metabolism; (3) Aspirin poisoning; (4) Administration of hyperconcentrated milk feeds; (5) Pyloric stenosis; (6) Severe gastroenteritis; (7) Diabetic ketoacidosis.

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  (5) Pyloric stenosis. There is a metabolic alkalosis and hypokalaemia due to depletion of H+ in the vomit. The timing (4–6 weeks), male sex, increasing vomiting and constipation, lack of bile and irritability are typical features. Acute renal failure would show a higher creatinine and hyperkalaemia. Concentrated feeds would cause hypernatraemia. Most of these conditions cause acidosis. The normal glucose excludes diabetic ketoacidosis. This child is too young to have accidentally ingested aspirin. Aspirin poisoning typically causes a respiratory alkalosis due to hyperventilation, then progresses to a metabolic acidosis.

• (e) What fluid would you use to rehydrate him and by what route? Can you calculate his fluid deficit in millilitres?

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  Normally, oral rehydration solution is the safest way to rehydrate this degree of dehydration, but as the child is likely to have pyloric stenosis this will not be absorbed. Intravenous dextrose–saline fluids are indicated, with added potassium to correct the hyperkalaemia.

  If this child is 8% dehydrated and weighs 3 kg then his fluid deficit is approximately 8% of 3 L. For this child, this would be (3300 mL /100) × 8 = 264 mL.

  The fluid prescription should include the child’s maintenance fluid requirement and this deficit, given over 24 hours. The maintenance fluid requirement is 100 mL/kg (for the first 10 kg), which 3.3 × 100 = 330 mL. The total fluids (over 24 hours) is therefore 330 + 264 = 594 mL (= approx. 25 mL/h).

• (f) What is the definitive treatment for this child?

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  This child has pyloric stenosis. Examination of a palpable mass in the epigastric area and visible peristalsis over the stomach after a test feed will confirm the diagnosis. An ultrasound scan may show a thickened, elongated pyloric muscle. The child must be carefully rehydrated prior to the definitive operation, which is Ramstedt’s pyloromyotomy.