The grieving family of a newborn baby who died after mistakenly being given nitrous oxide has accused hospital staff of “pumping poison into him”.

Baby John Ghanem, who was supposed to receive oxygen, died less than an hour after being born at Bankstown-Lidcombe Hospital on July 13.

His uncle Joe Kharma said the family want justice for baby John.

“He was killed for nothing,” he told 2GB radio.

“They just kept pumping poison into him.”

The newborn was whisked away from his mother Sonya Ghanem, who says she woke up from a caesarean section general anaesthetic to be told her baby was dead.

“I said `I want to see him’. (I was) just looking at him, shaking,” she told the Nine Network.

“‘Wake up’, I would tell him, `wake up, wake up. What did they do to you’.”

Instead of taking her son home in a baby capsule he was laid into a little white coffin last week.

The family only learned of the fatal mix-up on Saturday.

Health officials have also revealed a baby girl is in a critical condition after also receiving nitrous oxide at the same hospital in June.

Ms Ghanem’s brother, David Kharma, said the family was devastated. Photo: ABC

Health Minister Jillian Skinner has apologised for the “devastating error” and announced a sweeping review of hospital operating theatres commissioned in the past five years.

Mr Kharma criticised Ms Skinner’s response.

“There’s been no support from the minister or government, they seem to be more worried about running an investigation,” he told AAP.

“The cause of death, knowing that baby John was poisoned, has been very hard for the family to accept.”

Ms Skinner, who has rejected calls to resign, said the faulty operating theatre has been closed and the coroner will investigate baby John’s death.

The error was discovered last Thursday when a paediatrician raised concerns.

NSW Health Minister Jillian Skinner is “profoundly sorry” over the tragedies. Photo: AAP

Initially it was thought that an oxygen machine was incorrectly installed and certified by gas supplier BOC Limited in July 2015.

But Ms Skinner says the fault occurred via a gas line, not a cylinder.

“I am assured that there are no other instances such as this,” she said.

Ms Skinner said she would not resign because she couldn’t have personally prevented the mix-up.

She also defended her decision to attend Monday night’s Helpmann awards at Sydney’s Lyric Theatre as news broke about the baby’s death.

“That was a long-standing arrangement, I was representing the NSW government,” she said.

NSW Opposition Leader Luke Foley called on Premier Mike Baird to dump Ms Skinner.

“Rather than reaching out to the family … she frocks up and goes to the theatre,” he said.

An independent investigation chaired by an obstetrician will be conducted into Southwest Sydney Local Health District while BOC Limited will conduct its own inquiry.

Lawyers say both families should claim compensation over “medical negligence”, even though no amount of money could make up for their pain.

“The baby girl who has sustained brain damage … has potentially been robbed of the opportunity to lead a normal, happy life,” a spokeswoman from Shine Lawyers said.

-AAP