The intensive care unit at Bristol Children's Hospital could come under pressure if swine flu takes hold this winter, according to new research.

A study released today has found that there may not be enough paediatric intensive care beds to meet expected demand.

Youngsters are one of the groups that have been most seriously affected by the H1N1 virus and hospitals are likely to suffer extra pressure this winter.

Estimates by a Cambridge University research team suggest that the increased demand of paediatric intensive care beds from patients being transferred by smaller hospitals may increase the pressure on regional specialist centres like the one in Bristol.

More than half of admissions to paediatric intensive care units (PICUs) are unplanned, and respiratory illness is the second largest cause of admission, accounting for around one in four cases. Seasonal respiratory infections place added pressure on their capacity.

The researchers used Department of Health and European Centre for Disease Prevention and Control recommendations to estimate the number of under-15s who are likely to require hospital care during the second wave of the pandemic. Based on data, they estimated that 3.8 per cent of the UK's population of under-15s admitted to hospital for swine flu would require critical care.

The study is due to be published in the Archives of Disease in Childhood. They said that because the majority of critical care admissions are unplanned there is little chance of cancelling planned surgery and procedures.

The authors said: "It seems inevitable that PICUs will experience significant additional pressure this winter from admissions due to the pandemic."

Hospitals have been planning their services to ensure that they can meet the demand for intensive care beds if the second wave of swine flu hits the area and patients with associated complications need additional care.

The main PICU in the city is at Bristol Children's Hospital, which will also take patients from district hospitals in the region.

The Children's Hospital is run by University Hospitals Bristol NHS Foundation Trust.

Spokeswoman Laura Treasure said the trust currently had 15 paediatric intensive care beds and can extend this capacity to 18 if required.

She said: "UH Bristol also has intensive care capacity available in a number of other areas across the trust and there is potential for this capacity to be utilised for individual paediatric cases on a case-by-case basis."

Frenchay Hospital also has four intensive care beds for youngsters in its specialist unit for neurology and burns. Plans are in place for the unit to double the number of beds if necessary to support the children's hospital if the pandemic puts too much strain on beds.

Richard Cottle, spokesman for North Bristol NHS Trust, which runs Frenchay, said: "The trust is acting as support to the PICU at the children's hospital as part plans."

There is no paediatric intensive care unit at Weston General and children who require support will be sent to Bristol Children's Hospital. A spokeswoman said the hospital was working closely with colleagues in Bristol.