Keegan's mum Carol said: "He's not good and ... on a ventilator, in a medically induced coma. Staff here are doing their best."
Mrs Brieske was in tears as she spoke to Hawke's Bay Today and said the family were "shattered".
"We nearly lost him on Saturday night and were just lucky a thoracic surgeon was in the theatre next to him.
"We've got the right team working with our boy, who is on so many machines."
The trainee Scanpower line mechanic's injuries were mostly to his left side, including a fractured skull, broken elbow and ribs two to 12 ripped and floating.
His left lung was ruptured and his right lung not much better.
"For this to happen now when Keegan has turned his life around is heartbreaking," Mrs Brieske said.
It was his father's worst nightmare finding him in the wrecked car.
"Trevor isn't well and the shock has knocked him around: he's having treatment from his specialist while we're down here in Wellington," she said.
"We're fortunate to have my sister down here and she's with us all the time but it's hard when the staff kick us out of Keegan's room because they have to do a lot with him.
"The doctors tell us they are managing his condition hour by hour and they're keeping him in a coma to manage his pain and to keep him relaxed while he's on the ventilator."
Preliminary indications suggest speed may have been a factor in the crash and Dannevirke Police, assisted by the Serious Crash Unit, were continuing to investigate, Senior Sergeant Nathan Davis said.
"Officers are speaking with the driver to ascertain how the crash occurred but it is too early to comment on any potential charges," he said.
