Shallow water blackout a deadly risk for swimmers

Senior lifeguard Jonathon Webber and, inset, Sam Goodenough. Photos / Michael Craig, Tim Cuff

The tragic death of a Nelson teenager this week serves as a warning of the risks of suffering from shallow water blackout when holding your breath underwater, a water safety expert says.

While the cause of 16-year-old Sam Goodenough's death has not yet been determined, his father Geoff confirmed his son had been competing with others to see who could hold their breath the longest.

Tragically, Sam failed to surface. Paramedics were called to try to revive him and he was taken to Nelson Hospital, where he lay on life support for five days before dying on Tuesday.

Police have referred Sam's death to the coroner as a suspected drowning.

But Jonathon Webber, a senior lifeguard, Auckland Hospital resuscitation officer and WaterSafe Auckland board member, said just because someone dies unexpectedly in the water doesn't necessarily mean it is a drowning, as they could have suffered a shallow water blackout.

"Just because someone died in an aquatic facility, you can't just put it down to drowning until you've looked at all the symptoms," Mr Webber said, acknowledging he was not yet aware of all the details of the death.

"If someone swimming has a cardiac arrest or epileptic seizure they just sink to the bottom. It's not the symptoms that present for drowning - people splash about."

Shallow water blackout occurs when the lungs have reduced levels of carbon dioxide in them. As the body's desire to breathe is brought on by a build-up of carbon dioxide in the lungs, if there is reduced carbon dioxide the brain is fooled into thinking there is not yet the need to breathe. With the brain short of oxygen, the victim faints and subsequently drowns.

Swimmers can suffer from a blackout when entering the water after exercising extremely hard - exercising lowers the oxygen level in the body - or by taking deep breaths in preparation for swimming under the water, as the body expels carbon dioxide from the lungs.

Mr Webber said the risks of breathing deeply ahead of entering the water are not well-known by the public.

"Virtually no one knows this is a dangerous thing to do," he said.

"I remember as a kid we used to have competitions to see who could swim underwater the longest.

"It's probably something as kids we've all done and didn't know how dangerous it was."

Mr Webber said blame is often pointed at lifeguards at public pools when someone dies as a result of shallow water blackout, but this is not fair.

"It's incredibly difficult - virtually impossible - [for poolside lifeguards] to see the outline of a body on the bottom of a pool when people are swimming and treading through water [above them]."

While Mr Webber hoped education would help ensure shallow water blackout does not happen in the first place, people need to be aware of what to do should they see someone at the bottom of a pool.

"If this was to occur, get them out of the water, call the ambulance, and start CPR. That's the message we want to get out."