One hundred and forty-one maternity workers at an NHS hospital trust in Essex are pursuing personal injury claims after being exposed to what they describe as hazardous concentrations of nitrous oxide while on duty at Basildon Hospital between 2018 and 2023. The claimants include midwives and healthcare assistants, each seeking compensation in excess of £1,500.

Entonox, commonly known as gas and air, is a mixture of nitrous oxide and oxygen administered to women during labour as pain relief. It is considered safe for patients. For staff working in the same rooms over extended periods, the picture is different. Nitrous oxide enters the air when women exhale, when gas lines leak, and when canisters are opened and connected to equipment. In poorly ventilated spaces, concentrations can rise quickly.

An internal hospital report found that staff had been exposed to nitrous oxide at levels up to 30 times the legal workplace exposure limit. The health consequences reported by claimants were wide-ranging: chronic fatigue, persistent headaches, anxiety, cognitive impairment and neurological symptoms including pain in the hands and feet. One midwife collapsed at work. Court filings list excessive fatigue and irritability among the documented effects. Several workers reported low vitamin B12, which contributed to heart palpitations and difficulties concentrating.

What compounds the situation is the manner in which staff learned of the risk. Internal documents show that workers were not informed of test results confirming the safety breaches for 16 months after those results were recorded. The trust later acknowledged that there had been unacceptable delays in responding to and mitigating a serious risk. That admission came in 2024.

Staff speaking anonymously describe a sense of having been badly let down. One described colleagues suffering from fatigue so severe it was chronic, alongside constant headaches and cognitive difficulties they had not experienced before working in the unit. They said those responsible needed to be held accountable. Another member of staff who collapsed at work reported headaches, low mood and anxiety among her symptoms. A third described pain in her hands and feet. Several claimants said the way they were treated had generated widespread anger among those affected.

The Mid and South Essex NHS Foundation Trust has already paid £89,000 in settlements to some of those who brought claims. Denise Townsend, the trust's acting chief nursing officer, said the organisation had learned lessons from the incident and improved its oversight of medical gas monitoring across the maternity unit at Basildon Hospital. The trust has since installed equipment designed to remove nitrous oxide from the air. Townsend acknowledged that the trust should have acted faster to address the issues when they arose.

The problem is not confined to Basildon. Elevated levels of nitrous oxide in maternity units have been identified at other NHS trusts across England, raising questions about whether existing ventilation standards and monitoring requirements are adequate for clinical environments where Entonox is in continuous use. No national review has been announced. The case is next due to be heard in court in July.