Researchers in the US have reported what they believe is a first-of-its-kind reversal of brain damage, after treating a drowned and resuscitated toddler with a combination of oxygen therapies.

The little girl, whose heart didn't beat on her own for 2 hours after drowning, showed deep grey matter injury and cerebral atrophy with grey and white matter loss after the incident, and could no longer speak, walk, or respond to voices – but would uncontrollably squirm around and shake her head.

Amazingly, thanks to a course of oxygen treatments – including hyperbaric oxygen therapy (HBOT) – administered by a team from LSU Health New Orleans and the University of North Dakota, doctors were able to significantly reverse the brain damage experienced by the toddler.

"The startling regrowth of tissue in this case occurred because we were able to intervene early in a growing child, before long-term tissue degeneration," says hyperbaric specialist Paul Harch from the LSU Health New Orleans School of Medicine.

The drowning occurred in February of last year, when two-year-old Eden Carlson slipped through a baby gate while her mother took a shower, then made it past a heavy door, before eventually falling into the family swimming pool.

She was in the water for 15 minutes before being discovered and had experienced cardiac arrest, and while her mother immediately began CPR, Eden wasn't successfully resuscitated for 2 hours, being eventually revived by doctors at Washington Regional Medical Centre in Fayetteville, Arkansas.

After receiving critical care in hospital for 48 days, the little girl was discharged, but due to the extent of her brain injuries and their physical side effects, Harch proposed treatment with oxygen therapies in an attempt to "wake up" Eden's damaged brain.

Hyperbaric oxygen therapy works by administering oxygen to a patient at an ambient pressure higher than atmospheric pressure, through the use of a sealed, pressurised chamber.

By doing this, the amount of oxygen in a patient's blood supply is increased, which can restore normal levels of blood gases and repair damaged tissue.

In this case, Eden wasn't located close enough to a hyperbaric oxygen therapy chamber, so the team began a bridging course of normobaric oxygen treatments – delivered at sea level pressure – at fifty-five days after the drowning.

The treatments, given for 45 minutes twice a day through a nasal cannula, saw Eden recover alertness and reduced her squirming, giving her back increased movement of her arms and hands.

She also regained part of her ability to eat orally, and could speak short sequences – and laugh.

About three weeks later, the researchers moved Eden and family to New Orleans, where she began a round of new treatments in a hyperbaric chamber.

After just 10 sessions, Eden's mother observed that the toddler was back to "near normal, except for gross motor function", and so the little girl began physical therapy in addition to the hyperbaric treatment.

Once 39 hyperbaric sessions were completed, Eden's walking had improved, and her speech level was assessed to be now greater than it was at the time of the drowning. She demonstrated improvements on all neurological abnormality tests, and showed near normal motor function and cognition.

At the conclusion of the treatment, some 162 days after she drowned, MRI scans revealed that Eden still bore a mild residual injury to her brain, but had experienced a near-complete reversal of cortical and white matter atrophy.

The team studying her recovery say that to their knowledge, this kind of reversal is "unreported with any therapy".

And while they don't fully understand the exact breakdown of this amazing revival in Eden's fortunes, it's clear that normobaric and hyperbaric oxygen treatments combined to reduce inflammation and promote brain cell survival.

"Although it's impossible to conclude from this single case if the sequential application of normobaric oxygen then HBOT would be more effective than HBOT alone, in the absence of HBOT therapy, short duration, repetitive normobaric oxygen therapy may be an option until HBOT is available," Harch says.

"Such low-risk medical treatment may have a profound effect on recovery of function in similar patients who are neurologically devastated by drowning."

The findings are reported in Medical Gas Research.

Update: Since this story was first published, other scientists have voiced their concerns about whether the oxygen treatments administered to Eden could explain her recovery as suggested in the study.

In comments made to Live Science, paediatric neurologist Ian Miller from Nicklaus Children's Hospital in Miami cast doubt on whether hyperbaric and normobaric treatments could deliver such a result.

"There is just no way that providing oxygen to a dead brain cell makes the brain cell recover," Miller told Live Science's Rachael Rettner. "That's not how the brain responds to injury and to oxygen once neurological death has occurred."

His concerns were shared by physiotherapist David Cifu from Virginia Commonwealth University, who said Eden's recovery was more likely due to factors other than hyperbaric treatment, which was unlikely to have restored her lost brain functions.

In separate comments, consultant anaesthetist Oliver Sykes from University College London told The Independent that there's no evidence that hyperbaric treatment can produce recoveries like this.

"I can't think of a reason why what has been reported would have happened, and I'd be very surprised if this was a repeatable result," he said. "I haven't heard of this kind of reported outcome before."

For what it's worth, the FDA warns people on its website that hyperbaric treatments have been touted to deliver a range of medical benefits for various ailments, but many of the results aren't clinically proven.

In response to his detractors, Harch told Live Science that Eden made "progressive accelerated neurological improvement with each week of HBOT…. Spontaneous recovery and growth of tissue can possibly occur over time, but the child was not improving at this rate until the introduction of each of these therapies".

As for whether the treatment and recovery in this instance were more than just a coincidence is unclear, but if Harch's claims are correct, hopefully future research into HBOT can clarify what's going on here, and whether we've got a truly viable solution to these kinds of brain injuries.

Until then, we're thrilled Eden has made the recovery she has, but have updated the article with these opinions to give a fuller picture on some of the questions surrounding this area of research.