The sirens screamed and blue lights flashed as the ambulance pulled out from the hospital.

In the back, two medics were strapped into their seats, calm and still despite the vehicle speeding down St Michael's Hill. Alongside them an empty incubator waited to be used.

A premature baby, just five days old, had become unwell and needed to be rushed to Bristol for detailed tests and possibly an operation, advanced neonatal nurse practitioner, Chris Ludlam explained.

The tot, born at 28 weeks, was being cared for in the neonatal intensive care unit (NI CU) at Bath Royal United Hospital (RUH), but when concerns were raised about possible complications the decision was taken to rush down the A4 to pick him up.

The Newborn Emergency Stabilisation and Transfer Team (NEST), based at St Michael's Hospital in Bristol, was set up to transport babies between hospitals.

Some hospitals cannot provide the dedicated care needed for some of the sickest babies, while others need to transfer youngsters due to the nature of complications, or simply because there is not enough space for them at a particular hospital.

Specialist nurses and doctors travel in the ambulance with a travel incubator and monitoring equipment so that the babies can be given the same level of care as in the NICU while on the move.

The vehicle is provided through the private Bristol Ambulance Service, which is contracted to NEST for the purpose of these transfers.

Hospitals ring a dedicated hotline. Depending on the urgency of the call, the team set off within minutes or an hour to pick up a baby.

Their main work takes them from St Michael's to all hospitals within the Western network – Southmead, Weston-super-Mare, Cheltenham, Gloucester, Swindon, Bath, Taunton and Yeovil – but they also return babies to Devon and Cornwall.

The service was set up from St Michael's because the majority of transports in the area were coming to the hospital so the natural progression was for it to become a hub.

Launched in spring 2008, the team has carried out 545 transfers for 352 babies.

The bulk of the most urgent cases are transported to St Michael's, which has a specialist surgical unit equipped to deal with the complex needs of the sickest babies, while others are taken to Southmead, which specialises in looking after the smallest of babies.

Neonatologist James Tooley has been a consultant at St Michael's for five years and has seen first hand the need for a transport service dedicated to transfers so that staff were not taken away from the unit to assist during the journey.

On the trip out of Bristol Mr Ludlam made calls to glean more details about the condition of baby Benjamin Skirrow and his medical background from doctors at Bath in preparation for arrival at the hospital.

He said: "A lot of the babies we move about have respiratory problems so we have ventilation and we can also provide pain relief. There are monitors to measure the heart rate and blood pressure. All in all, it is like a mini intensive care unit on the move.

"We need to move babies in a good condition and stable. If there is any doubt about that we should leave them."

The youngster was stable but there were concerns about his bowel and fears that it may have twisted. Doctors suspected he might need surgery to correct a problem, which locally could only be carried out at St Michael's.

At RUH the NEST team were introduced to Benjamin and the two teams worked together to prepare him for the trip to Bristol.

The NEST team also took the time to speak to the parents so they understood what was happening and where their child would be taken.

There is no room in the ambulance for the family to travel with their baby, but they are given an information pack complete with map and are asked for a mobile telephone number so the team can keep in contact with them and notify them of arrival at the destination hospital.

Parents Amanda and David were given the time to say goodbye to their son before the ambulance staff took him into the vehicle for the transfer.

An hour and 20 minutes after arriving at Bath, the handover was complete and the team were ready to return to Bristol.

Throughout the journey, the team kept an eye on the baby's breathing, temperature and other monitors to ensure there were no problems to be dealt with.

Mr Ludlum said that if anything did change they would stop the vehicle and carry out any intervention by the side of the road.

After a 25-minute journey on blue lights, the ambulance pulled into St Michael's and Benjamin was taken up to the NICU and transferred into another cot in the reverse of the process carried out at Bath.

The youngster was sent for X-rays and checked over by specialist doctors and returned to the travel incubator for a journey back to the RUH's NICU the next day for dedicated support until he is strong enough to leave hospital.