Daniel was 3 weeks of age when his parents took him to casualty. He had not been feeding well during the previous 12 h. Vomiting was now their main concern and what worried them more was the colour of the vomitus which was green.

He was the first born child to a healthy non-consanguineous Caucasian couple. The pregnancy had been uneventful. The first fetal anomaly scan had been performed at the local hospital and the rest abroad. The scans were not available, but the report indicated an absence of any major anomalies. He was born at full-term by normal vaginal delivery. He was in good condition at birth and cried instantly. His birth weight was 3200 g. He was initially breast fed and settled. He had passed meconium normally. Postnatal examination had revealed a small right-sided hydrocoele. He was discharged from hospital at 6 h of age.

At presentation (11.30 am) Daniel appeared dehydrated. The heart rate was 170 beats/min, respiratory rate 60/min and temperature 37.8°C. The oxygen saturation in room air was 99–100%. The chest was clear to auscultation. A non-radiating soft systolic murmur was heard over the praecordium. The abdomen was flat and appeared to be tender. He had wet nappies that morning.

The casualty SHO considered the possibility of sepsis. The results of investigations undertaken are shown in table 1.

A 20 ml/kg bolus of intravenous normal saline …