NHS maternity staff who were exposed to excessive levels of nitrous oxide have received “landmark” payouts totalling £735,000, a union said.

Basildon Hospital in Essex settled claims from 121 staff, including 85 midwives, who took legal action after reporting fatigue, anxiety, headaches and “brain fog” after the gas levels breached safety limits.

The Mid and South Essex NHS Foundation Trust said it had apologised to staff.

The Royal College of Midwives (RCM) said it was the largest group legal action ever brought by midwives in the UK.

The gas, also known as Entonox, is used to provide temporary pain relief for women giving birth.

The staff members behind the claims were found to have breathed it in over long shifts for months and years.

According to an internal report from Basildon Hospital, some members of staff were exposed to levels up to 30 times higher than the legal workplace exposure limit between 2021 and 2023.

They were also not told for 16 months about test results commissioned by the trust that showed their exposure had breached safety thresholds.

The legal action was first revealed by the BBC in May.

The trust settled the claims after admitting its staff had been exposed to dangerously high levels of the gas.

NHS Resolution, which manages legal claims and compensation cases on behalf of the NHS in England, confirmed the payouts.

A spokesman said: “We can confirm that 121 claims have been settled for a total of £735,000. Some other claims remain outstanding. We are unaware of any larger group of claims brought by midwives.”

One claim has yet to be settled according to the RCM.

Daniel Poet, from Thompsons Solicitors, who represented the workers, said: “We are proud to have secured compensation for our clients, but they should never have been put at risk in the first place.”

“The trust knew about the dangers in 2021, but staff weren’t told until the following year and it took another year for safety measures to be introduced. That delay is unacceptable,” he added.

Gill Walton, the RCM chief executive and general secretary, said: “For years, midwives at Basildon were breathing in nitrous oxide at dangerous levels while they cared for women and babies.

“Even once the problem had been discovered, it was more than a year before staff were told. That is simply not acceptable and no midwife should ever be treated that way,” she said.

She continued: “This is a landmark settlement for our members and it should make every NHS employer sit up and take notice. If you don’t protect your staff – the RCM will hold you to account”.

The RCM has also written to every NHS trust in England to make them aware of the risks of the gas and said it had also “raised concerns about the trust’s lack of action” with the Health and Safety Executive (HSE).

The RCM has since worked directly with the HSE to update and improve guidance on the use of Entonox.

Louise Crosby, the chief nursing and quality officer for the Mid and South Essex NHS Foundation Trust, said: “We have acknowledged that we should have acted faster to address the issues and have apologised to staff.

“Since the incident we have learnt lessons, and as part of this, we have improved our oversight of the monitoring of medical gases across the maternity unit at Basildon Hospital.”

The trust added that it had installed scavenger equipment at the maternity unit and that women could have confidence that it is safe to use Entonox.

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