Medical tests showed "nothing to explain" why a baby deteriorated, Lucy Letby's trial hears.
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Dr John Gibbs, a consultant paediatrician, said Child J had been making "steady, acceptable and encouraging progress".
He added that within two-and-a-half weeks, Child J had moved on to bottle feeds and was "fine" and without any respiratory complications.
"It was a challenge managing Child J's stomas because we rarely had babies with a stoma needing recycling feeds [at the Countess of Chester Hospital]," he said.
He added this was discussed with the neonatal team at Alder Hey Children's Hospital, who dealt with stomas "fairly frequently", and they "were satisfied with her progress".
But in the early hours of 27 November 2015, Child J suffered seizures and four desaturations with her heart rate also dropping on the third and fourth occasion, the court heard.
"Both occurring together is of more concern than one occurring by itself," Dr Gibbs told the court.
Dr Stephen Brearey, who reviewed medical tests carried out that day, said "nothing explained" why the infant had collapsed.
"She [Child J] normalised very quickly over the course of the day and all the investigations we had undertaken couldn't identify why she had the desaturations or explain why she had a seizure.
"I do know hypoxia causes seizures so that would be possibly the most likely cause.
"There remains the question why was [Child J] hypoxic when two or three weeks beforehand she had been breathing normally in air and there was no suggestion of infection.
"In fact, we stopped antibiotics 36 hours after starting them because there was no evidence of infection in the blood tests and she remained well for weeks afterwards."