THE parents of a Freestone boy who had his life torn apart when he sustained severe brain damage after a heart operation are suing a hospital $8.5 million for medical negligence.

Dustin Mauch was a baby when he had surgery at Brisbane's Mater Hospital in 2009 for a hole in the heart.

Within 48 hours, Dustin developed sepsis from infection and other complications, resulting in three cardiac arrests and multi-organ failure, according to the claim lodged in the the Supreme Court.

The Mauch's once happy, responsive 11-month-old was left with vision and speech problems and will require lifelong care costing thousands of dollars a week, it is alleged.

Dustin, who is now aged eight and has a healthy heart, had been otherwise developing normally for his age before his brain injury.

Lawyer Bill King of Shine Lawyers in Brisbane said Dustin's post-surgery condition was not addressed by medical staff.

"There were a series of red flags over a period of 12 to 18 hours that we allege were overlooked and not properly dealt with,” Mr King said.

He said Dustin could live into his 70 or 80s and will require a lifetime of full-time care by his family and disability workers. He will also require educational support and specialist medical treatment.

Mr King said Dustin's heartbreaking case was magnified by his family's proximity to major hospitals and facilities.

"Some families in a similar situation have transferable occupations such as a nurse or a mechanic and can move closer to facilities,” Mr King said.

"But Dustin's parents are dairy farmers with four other children and like most people living on the land they can't relocate.”

The $8.5 million claim was based on medical negligence leading to a person requiring full-time care and supervision at enormous cost, Mr King said.

"Dustin's carers will require an appreciation of a person with disabilities and if his parents can't be there to look after him, he will need trained staff, which can cost thousands of dollars a week,” Mr King said.

"It becomes extremely expensive when a person with a disability can't travel and carers are required to come to them, particularly in outer regional areas.”