Kenneth William Attenborough, 43 of Minto, pleaded guilty this week to poisoning his father with the intent to murder him on May 10 last year.

The court heard Attenborough broke into the box containing the remainder of the day's intravenous pain medication and administered it to his 82-year-old father in one go.

When it was ineffective, he tried to smother his father and when that also failed he used a syringe to inject whiskey into a tube in his stomach.

When the measure caused pain, he gave up and broke down, apologised and reported the incident to a nurse at Uniting Wontama Orange where his father was a resident - senior staff were then informed and police were called.

Agreed facts put before the court detailed a recording made of a conversation between father and son a year earlier where his father supported ending his own life in the right circumstances.

A video made on the day of the incident recorded Attenborough asking his father if he consented to drinking the whiskey and having the medication administered and his answer, "yeah, yep".

His father suffered no harm as a result of his son's actions and died on May 30 from unrelated causes.

Attenborough gave tearful evidence in court on Wednesday, saying his mother had suffered brain cancer and he had cared for her at home after chemotherapy failed.

He told the court amid his mother's discomfort and humiliation, she also asked him to help her die.

"I stopped allowing myself to be in the same room as her because I couldn't stand to see her disappointment in me every time I said no," he said.

He said he carried the emotional burden for several years after his mother's death and when his father suffered twisted bowels and ongoing pain and infection with a three-month prognosis, the distress returned.

He said he had been diagnosed with depression and post-traumatic stress disorder.

Crown Prosecutor Chris Bailey acknowledged Attenborough did not have anything to gain from killing his father, but his actions were illegal in NSW and his punishment needed to deter others from contemplating doing the same.

"As we live longer, these cases will become more and more frequent," he said.

Acting Judge Geoffrey Graham said the court could only deal with the law as it stood, but he made one observation.

"Medical science has been really effective at prolonging life but not quite as effective at easing passing," he said.

He was satisfied there was a causal link between Attenborough's mother's suffering, his mental illness and the events on May 10.

He was also satisfied his father was in a considerable amount of pain, but of sound mind.

He judged jail would be a poor place to attempt his mental recovery.

"His references say he is kind, honest, reliable, compassionate and selfless - this is a case where his good character could be said to lead him to the commission of this offence through his desire to relieve his father of a painful and humiliating death," he said.

Taking into account the early guilty plea and remorse, Judge Graham handed down a 20-month intensive corrections order.

Attenborough will have to complete 100 hours of community service and continue with his treatment.

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