Damian Jack Power, 24, of Geelong, had been having a psychotic episode due to effects of the drug ice when he stabbed Ballarat police Senior Sergeant David Reither four times on the side of the Midland Highway near Geelong about 8.30pm on August 21 last year.

Sentencing Power to a maximum term of four years and eight months' jail in the Melbourne County Court on Thursday, Judge Gerard Mullally said Senior Sergeant Reither had been trying to offer assistance to Power after noticing him on the side of the road with his girlfriend.

The court heard Power, who had that morning been released from the psychiatric ward of a Geelong hospital, was the passenger in a car driven by his girlfriend and had pulled on the hand brake while they drove at full speed, causing the car to spin 180 degrees on the highway.

Judge Mullally said Senior Sergeant Reither, who was in a marked police car on his way back to Ballarat, pulled over to render assistance.

The judge said Power had become "quite disturbed" after using ice in the lead-up to the offending, adding he was completely irrational and believed there had been some sort of creature in the back of his girlfriend's car.

The court heard Senior Sergeant Reither assured Power and his girlfriend that he could help them, but Power attacked the officer as he was calling triple zero, stabbing him four times in the side of his abdomen.

Judge Mullally said the officer had to be air-lifted to a Melbourne hospital for emergency surgery, with injuries including a fractured rib near his heart and cuts to his diaphragm and spleen.

The court heard Senior Sergeant Reither rang his wife while bleeding on the side of the road, not knowing whether he'd live to see her or his son again.

Judge Mullally said it was only days before, on August 18, that Power took a hunting knife to his Geelong work place and threatened fellow staff members, he also threatened two police constables who attended the scene, asking them to shoot him.

The judge said it was violence "so out of proportion and so out of character", adding Power had been in the midst of a psychotic episode because of his drug use.

He said Power had been a young and hardworking man of good character, with no prior convictions.

"You were a quiet and gentle young man with a lot of potential," Judge Mullally said.

"The one unstable aspect of your life was your use of drugs."

The court heard Power had used cannabis from his early teens, slowly progressing to ecstasy, magic mushrooms and then ice.

Power pleaded guilty last week to charges including reckless conduct endangering a person and intentionally causing serious injury.

Judge Mullally said Power had strong prospects of rehabilitation and that a lengthy jail term wasn't warranted due to a number of "out if the ordinary" mitigating factors.

He said the main mitigating factor was that Power had been psychotic and unwell when he offended, adding he was now mentally well again.

The judge ordered that 301 days of pre-sentence detention be counted as time served.