With the rest of the 18cm handmade weapon he then repeatedly stabbed a Corrective Services officer in the neck, not stopping even when sprayed with a chemical agent.
More than two years later, Venzlouskas, 28, received a nine-year prison sentence in Brisbane District Court, appearing in shackles and handcuffs flanked by four Corrective Services officers.
In July 2020, Venzlouskas was remanded in custody in Brisbane's south when guards attended his cell to address a previous incident involving violence against another inmate.
Without warning, Venzlouskas punched one guard five to six times, knocking him to the ground.
He then attacked the second Corrective Services officer, punching him in the head with his hand holding a shiv.
The force of the blow broke off the end of the shiv which became embedded in the officer's eyelid.
Venzlouskas pushed the second officer to the ground and got behind him holding the shiv to his neck "effectively taking him hostage".
He made repeated threats to harm and kill the second officer as the other tried to negotiate with him.
After about five minutes Venzlouskas violently stabbed the second officer in the neck at least three times and did not stop even when sprayed with a chemical agent before ultimately being restrained.
He later told police that he had planned the attack and crafted the shiv because he wanted to take a hostage so he could demand drugs.
Venzlouskas has struggled with drug use, mainly methamphetamine.
He had been exposed to significant domestic violence during his childhood, with his father attempting to kill him on numerous occasions, the court was told.
Growing up, his father had placed him in rooms locked away from the rest of the family, thrown gasoline at him and attempted to hit him with a brick and stab him, the defence barrister said.
Since he was 10 his primary carer was his mother who had a significant mental illness.
He was also sexually abused as a teenager by a trainer at an athletics club which resulted in "significant ongoing trauma", court was told.
A psychiatric report said it was likely Venzlouskas had a mixed personality disorder with strong anti-social and psychopathic tendencies but could not confirm whether he had a major psychotic disorder.
The report said he would require considerable therapy to reduce the risk of violent reoffending but concluded there was "no readily available psychotic explanation" for the 2020 prison assaults.
Venzlouskas was sentenced by Judge Amanda McDonnell after he pleaded guilty to charges including two counts of malicious act with intent.
A serious violent offence order was made, ensuring he must serve 80 per cent of his sentence before he is eligible for parole.
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