Hospitals in Colchester and Ipswich have stopped using a greenhouse gas in anaesthetics which damages the environment.
Nitrous oxide is known to cause damage to the ozone layer and contribute to global warming.
Anaesthetists at the East Suffolk and North Essex NHS Foundation Trust (ESNEFT) are now opting for greener alternatives.
But for parents-to-be concerned about pain relief during labour, nitrous oxide - often referred to as entonox or gas and air - remains an option.
The decision to stop using the gas is part of the commitment by the NHS to be carbon net zero by 2040.
Dr Kate Gardner, a consultant anaesthetist at Colchester Hospital, highlighted the damaging effects of the gas.
She said: "Nitrous oxide is incredibly damaging and has 300 times the global warming potential of carbon dioxide.
"It remains in the atmosphere for 114 years.
"The impact on global warming and climate change has come to the fore and many anaesthetists have stopped using it altogether."
The gas is responsible for two per cent of the NHS carbon footprint, and 75 per cent of the anaesthetic gas footprint.
Much is wasted due to leaks.
"Some studies show 95 per cent wastage from the piped supply," said Dr. Gardner.
"We made the decision to remove all piped nitrous oxide and dismantle the manifold.
"We have kept a cylinder supply for our two delivery suite anaesthetic machines, where we may still use it for limited cases.
"We should all be very proud, and hopefully other hospitals will follow our example."
Colchester and Ipswich Hospitals have also removed another anaesthetic agent called desflurane because it is harmful to the environment.
Dr Aaron Pennell, acting consultant anaesthetist and clinical lead for anaesthetics at Ipswich Hospital, spoke about the ongoing changes.
He said: "Our new operating theatre suite at Ipswich no longer has piped nitrous oxide and we are now in the process of dismantling the nitrous oxide manifold at Ipswich Hospital that serves all other operating theatres."
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