An NHS trust has been accused of a “failure to act with candour” and not acting swiftly enough to protect staff from hazardous exposure to nitrous oxide.

An independent review has concluded that there was an “unacceptable delay” in Mid and South Essex NHS Foundation Trust’s response to concerns about dangerous levels of the gas in the maternity unit at Basildon University Hospital maternity unit.

The review, conducted by the Good Governance Institute, also found the trust “failed to act with candour and transparency” over the incident.

While we now have robust systems in place and are confident that nitrous oxide levels are well within the safe limits, it is simply not acceptable that we took so long to act

“The inquiry found that there was an unacceptable delay in responding to and mitigating a serious risk that had been reported into the levels of nitrous oxide on the Basildon University Hospital maternity unit,” the authors wrote.

As a result, midwives and other staff on the maternity unit were “exposed to unnecessary risk or potential harm”, they added.

The review states that the levels of nitrous oxide – also known as Entonox – found on the ward “needed to be treated as a significant risk to health” when concerns were raised in July 2021, but this was not done until October 2022.

The NHS maternity survey for 2022 shows 76% of women used gas and air (nitrous oxide) during their labour.

I would like to sincerely apologise to the staff in the unit and thank them for their patience and their unwavering commitment to the families who use our maternity service

While there are no harmful side effects to using gas and air for a mother or baby, prolonged exposure can lead to health issues.

Mid and South Essex NHS Foundation Trust chief executive Matthew Hopkins said: “While we now have robust systems in place and are confident that nitrous oxide levels are well within the safe limits, it is simply not acceptable that we took so long to act.

“We committed to commissioning an independent investigation to fully understand what went wrong and how we could ensure that it doesn’t happen again.

“I would like to sincerely apologise to the staff in the unit and thank them for their patience and their unwavering commitment to the families who use our maternity service.”

A trust spokesperson said the organisation had made an action plan to address the recommendations set out in the report and had also commissioned a separate governance review.