In 2011, a baby named Tully Oliver Kavanagh died from hypoxic-ischaemic encephalopathy in Adelaide.

Tully was a twin. His mother, against her GP's advice, had opted for a planned homebirth where the only medical supervision was provided by former midwife and homebirth campaigner Lisa Barrett.

Baby Ruby, who would've been Tully's sister, was born first, healthy.

Then the unborn Tully's heart rate dropped and his mother noticed a huge blood clot.

She was rushed to hospital in the family car.

Partway there, the driver pulled over, and Tully was born.

When he arrived unconscious at the Women's and Children's Hospital, clinicians managed to resuscitate him, but diagnosed brain damage that was, in the coroner's words, "incompatible with life".

The case is significant because in June this year after a long investigation, police decided to bring manslaughter charges against Ms Barrett, alleging that her care of Tully's mother was so negligent it required criminal punishment.

Medical manslaughter cases are rare in Australia. Since the first case 165 years ago, just four doctors have been convicted of the offence and two of those date back more than 100 years.

Some legal commenters, such as law lecturer Associate Professor Ian Dobinson, have argued this rarity means prosecutors are confronted with a grey area of the law, leading to some cases not being pursued through the courts.

"In hospitals, there's a really high rate of what's determined to be 'avoidable death'," says Professor Dobinson, from the University of Technology Sydney.

"That suggests the treatment somewhere, somehow has been negligent."

He points to the Bankstown-Lidcombe Hospital, in Sydney, where a baby died in 2016 after nitrous oxide was administered instead of oxygen.

"How do you make such a mistake, other than circumstances of gross negligence?

"But we see no prosecution. Why? Is it too hard?"

As Professor Dobinson wrote in a 2009 paper for the University of Queensland Law Journal, manslaughter charges are more common in the UK than in Australia.

"In the UK, it seems to suggest a greater propensity of their Crown Prosecution Service to prosecute doctors, and there seems to be a reasonable likelihood of conviction," he says.

"While the law there and the law here are in principle the same, there's the difference — a willingness to prosecute."

The number of UK prosecutions also spiked after the high-profile conviction, of anaesthetist Dr John Adomako, who failed to notice an alarm sounding when a patient's breathing tube fell out during an eye operation.

In the 20 years before R v Adomako, in 1990, there were two UK medical manslaughter cases. In the following 10 years, the number rose to 13.

In the UK, as in Australia, prosecutors can only proceed if they believe a case is likely to succeed. The Adomako case showed UK prosecutors that manslaughter convictions were possible.

It was for this reason that some lawyers in Australia thought the case of Dr Jayant Patel — a man branded 'Dr Death' as a result of his alleged incompetence — would be the game-changer.

After a newspaper exposé and mass media coverage, an independent inquiry was launched, where surgeon Dr Peter Woodruff found that Dr Patel's substandard surgical care contributed to 13 deaths and may have contributed to another four.

Manslaughter charges were eventually laid in 2010 and Dr Patel was found guilty of killing three of his patients.

The Crown alleged that there had been poor decision-making and misdiagnosis, with surgery performed on inappropriate patients and the removal of healthy organ. The jury agreed that Dr Patel's decision to practise beyond the scope of his abilities was grossly negligent.

He was sentenced to seven years in jail. But Dr Patel appealed.

The High Court of Australia filleted the court's conviction with a surgical knife.

Prosecutors had gone wrong in originally telling the jury that Dr Patel's gross negligence was a result of his poor surgical skills, but then, 43 days into the 50-day trial, radically changing track to argue that it was Dr Patel's decision to operate, not his actual skill during the operation, where the gross negligence had occurred.

The High Court found this approach was a serious miscarriage of justice and quashed the conviction.

At the retrial, Dr Patel was subsequently cleared by the jury of manslaughter. He was 'Dr Death' no more.

Professor Dobinson says until the High Court appeal, people assumed the conviction of Dr Patel would provide significant legal clarity on the sort of acts or omissions that make up medical manslaughter.

"To a certain extent, it looked like we had a useful case in the form of Patel," he says.

Instead of giving a clear indication of how grossly negligent a doctor would have to be in their practice before a manslaughter conviction would stick, the case merely showed that the benchmark was somewhere higher than Dr Patel's failings, somewhere still not clearly defined.

It is worth stressing not everyone agrees with Professor Dobinson. Lawyer Bill Madden, a specialist in personal injury law, says it's not that prosecutors are too nervous to pursue medical manslaughter cases.

"I think they'd be cautious, but I wouldn't go as far as to say they're unlikely [to pursue cases]," says Mr Madden, Special Counsel at Carroll & O'Dea Lawyers in Sydney.

To non-lawyers, it may seem like the law is too vague, but Mr Madden says it's the way things are.

As frustrating as it might be for prosecutors trying to gauge the success or otherwise of their case, Mr Madden says there are unlikely to ever be specific markers signifying what makes a manslaughter charge stick.

"The law develops in a piecemeal way, where it considers each case."

But tempering statements such as this have not doused the interest in the upcoming trial of Lisa Barrett. Her next court appearance, her second so far, is slated for October. She is yet to formerly enter a plea.

When news broke of the charges, the local newspaper in Ms Barrett's hometown of Adelaide was spruiking the case as a global precedent. Whether this proves to be true or just a perverse form of hometown bias, medical defence organisations will be watching the trial with great interest.

Medical manslaughter convictions

The main legal clues to how Australian courts tackle medical manslaughter cases are the four successful convictions that researchers have identified. Perhaps reassuringly, there are consistencies visible even across the centuries.

Dr William Valentine (1843)

The first Australian doctor convicted of manslaughter, the Tasmanian Dr Valentine, admitted giving a patient a bottle of laudanum instead of the black draught he meant to.

He was found guilty but escaped with a £25 fine.

Dr Frederick Hornbrook (1864)

Dr Hornbrook, from Goulburn in regional NSW, was found guilty of manslaughter after administering 210 drops of sulfuric acid to an adult patient — 13 times the maximum dose.

The court sentenced him to two years' jail, sparking a lobbying effort from local doctors in private practice, who opposed the result. After just one month in jail, Dr Hornbrook received a royal pardon.

Dr Margaret Pearce (2000)

Almost 150 years later, Brisbane GP Dr Margaret Pearce was convicted after a similar error.

Dr Pearce injected a 15-month-old girl with morphine to stop the girl struggling and allow Dr Pearce to examine her burnt hand, according to a report in the Lancet.

The morphine dose was 15mg, about 10 times the required amount. The girl died overnight.

The court sentenced Dr Pearce to five years' jail, suspended after six months.

In 2003, while serving the suspended part of her sentence, Dr Pearce's registration was reinstated.

Dr Arthur Garry Gow (2006)

In another case reflected across centuries, Dr Gow prescribed a patient five ampules of morphine tartrate, instead of morphine sulfate.

The patient died after self-administering 120mg of the morphine tartrate to treat chronic back pain.

Like Dr William Valentine, who had also mixed up medications, Dr Gow was convicted of manslaughter.

He received an 18-month suspended sentence.

Justifying the suspended sentence, the judge said system failures had contributed to the death and the sentence was "to recognise that people, even professional people, make mistakes".

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