The Coroner in the inquest of baby Rohan Rhodes, who died at St Michael's Hospital, says there were "lost opportunities" in his care.
Rohan, who was born 15 weeks premature in Wales, died after being removed from a ventilator after being transferred to St Michael's in Bristol.
Flax Bourton Coroner's Court heard the medical team's plan was to keep Rohan on the ventilator ahead of upcoming heart surgery.
But advanced neonatal nurse Amanda Dallorzo took the "autonomous" decision to remove the machine and put a breathing mask on Rohan instead.
His condition deteriorated and he developed NEC, a gastrointestinal disease, which required surgery.
He never became stable for the operation and he died, aged just 36 days.
Avon Coroner Maria Voisin recorded a narrative verdict following a three day inquest into Rohan's death.
Rohan Rhodes was an extremely premature baby who was at risk of developing NEC.
He developed this condition which caused his death on September 30.
On September 29, there were three occasions when he should have had a blood gas test.
It is not known what results would have been, but these were lost opportunities which may have resulted in Rohan receiving earlier medical care.
The coroner says there were "lost opportunities" in the care of a premature baby who died after being removed from a ventilator.
A nurse at the inquest into the death of premature baby Rohan Rhodes at St Michael's Hospital in Bristol hospital has given evidence.