Two senior paramedics noticed a man trapped in a Melbourne car crash was breathing but still wrongly pronounced him dead and can't explain why.

A review of medical logs showed both paramedics agreed that Daniel Huf was breathing when they examined the 30-year-old in the wreck of his upside-down car in an Bacchus Marsh smash, but still declared him deceased and left the scene, Ambulance Victoria said.

Ambulance Victoria CEO Greg Sassella said a review into the bungle had failed to determine why the paramedics acted the way they did, and that they themselves could not explain their actions but were devastated and filled with regret.

"We don't know why the error occurred. The paramedics can't explain their actions other than to say that if they had the same case they would do it differently," Mr Sassella told reporters on Friday.

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"They noted that the patient was breathing and yet equally pronounced the patient as deceased."

Mr Sassella said the case was extremely unusual and one he'd never seen the likes of before. He believed the sheer pressure of the crash scene may simply have triggered a bizarre lapse in the paramedics' judgment.

Both paramedics were receiving counselling and had not yet returned to work, he said.

"I suspect it will take them some time to get over this. They're both good people, however, it is a mistake that is obviously quite grave," Mr Sassella said.

"It is something we need to try and learn more from again, but obviously people react differently under extreme pressure and I suspect it's something to do with that."

- AAP