Michael de Guzman is on trial in Downing Centre District Court after pleading not guilty to 11 charges including shooting Police Sergeant Luke Warburton with intent to murder at Nepean Hospital in January 2016.

The dog squad officer testified on Tuesday he believed he was going to die and has had 14 surgeries on his leg.

De Guzman's barrister, Sam Pararajasingham, said "there is no dispute as to the physical acts alleged by the Crown" but the charges would be defended on the grounds of mental illness.

In his opening address, crown prosecutor Mark Tedeschi QC said de Guzman had suffered a mental illness for nearly four years prior to the events which involved "an increasing paranoia" that his wife was having affairs.

This then morphed into the Filipino man believing his wife had fallen prey to a criminal group, Mr Tedeschi said.

The Crown alleges de Guzman "had not engaged in any aggressive, violent acts in that time (and) his delusions and aggressions on the day in question would not have occurred but for his use of the drug ice".

The 41-year-old was allegedly seen waving a walking stick above his head on a Colyton road and shouting "they're all coming" before he assaulted responding police in a "furious struggle".

He was later restrained by all four limbs to a hospital bed and under police guard before the decision was made to grant him bail and the restraints were removed, the prosecutor said.

De Guzman allegedly said: "I need to use a phone to call the federal prostitution hotline, the Russian mafia have my wife in a prostitution ring."

He is then accused of asking a doctor to help with his bed before he grabbed her, dragged her to the ground and held scissors to her throat for more than 20 minutes.

Sgt Warburton was nearby in his vehicle and responded to the triple-zero call.

The officer twice deployed capsicum spray into de Guzman's face and tried to push the scissors away.

"What ensued ... was a furious melee," Mr Tedeschi said.

De Guzman allegedly "took hold" of Sgt Warburton's firearm and fired two shots, the first at close range above the officer's pubic bone, severing his left femoral vein, and the second hitting a security officer in the leg.

Another guard suffered a shrapnel wound from a ricocheting bullet.

Senior Constable Tim Duffy grabbed the gun, which remained in de Guzman's clutch, and blocked the slide of the Glock 22 with his finger to prevent further shots, the prosecutor said.

De Guzman then allegedly told one officer: "Your friend is dead. The policeman is dead. You're all a part of it."

"It was quite clear he was still well-affected by a drug," Mr Tedeschi said.

The judge-alone trial before Judge Christopher Robison continues.

Australian Associated Press