THE LONG DIVE: POLICY RELATING
TO BREATH-HOLDING AND
PRE-IMMERSION HYPERVENTILATION
Authors: John H Pearn1,2, Richard C Franklin1,2,3, Amy E Peden1,3
Affiliations: 1 Royal Life Saving Society – Australia, 2. Department of Child Health,
Royal Children’s Hospital, University of Queensland, 3. College of Public Health,
Medical and Veterinary Science, James Cook University
INTRODUCTION
Recent media has highlighted the
dangers related to activities involving
breath-holding and pre-immersion
hyperventilation1,2. These potentially
dangerous activities can result in what is
commonly called ‘shallow water blackout’
(SWB), where an immersed person loses
consciousness due to a lack of oxygen.
There are on average 2 deaths each year
in Australia 3.
The activity of breath-holding is common and often
an essential part of some underwater sports, such
as underwater hockey, synchronised swimming
and free-diving (the activity of seeing how deep/
far a person can swim on one breath). It also
occurs recreationally while trying to swim as far
as possible underwater on a single breath. In the
past, endurance underwater swimming has been
a featured event of swimming carnivals with one
school awarding the ‘Long Dive’ medal4. Pre-dive
hyperventilation is also used by some occupationally,
although used more commonly in low and middle
income countries to fish, gather pearls or make
repairs to boats.
While associated with endurance underwater
swimming, other differential diagnoses include:
•Voluntary endurance underwater swimming with
pre-submersion hyperventilation
- Hypoxic seizures (convulsions) can result from
hypoxia following pre-dive hyperventilation.
•Hypoxic triggering of cardiac dysrhythmia
consequent upon pre-existing genetic or acquired
electrical conduction abnormalities of the heart.
•Cardiac dysrhythmias secondary to the normal
diving response, conduction defects sensitised by
pre-existing cardiac conditions.
•Association with the normal physiological “cold
shock” response5.
It is important that a genetic autopsy following
unexpected drowning in young people including
SWB is undertaken. It is best practice, if a coroner
identifies a good swimmer who drowns, for the first
degree relatives (parent, child or full siblings) to also
be tested.
CASE STUDY ONE
Figure 1: Effect of hyperventilation on breath holding7
A 19 year old man drowned at Hutchison
Reef free-diving. Authorities said he was
with 3 friends when he blacked out near
the surface and sank 30 metres in “what
appeared to be an unconscious state.” He
was brought to the surface after his friends
dove 30 metres without breathing to
retrieve his body, however he could not be
revived. The group had gone out for the
day spear fishing and free-diving.
Breath-hold after
normal respiration
PO2
Breath-hold after
hyperventilation
Stimulus to breathe
PCO2
Start of
breath-hold
Normal
breathing
Prior
hyperventilation
End of
breath-hold
Time
KNOWN DEATHS RELATED TO SHALLOW
WATER BLACKOUT IN AUSTRALIA: 2002-2012
Drowning deaths associated with Shallow Water
Blackout in Australia commonly fall into one of
three categories:
•Free-divers and spear fishermen – most commonly
in the ocean
•Those training to compete in activities such
as underwater hockey or free-diving – most
commonly in public pools
•Those recreating in home swimming pools and
holding breath either as a prank or challenge
Between 1 July 2002 and 30 June 2012, there were
16 deaths known to be related to SWB. 8 deaths
involved males between the ages of 16 and 35
swimming laps underwater, in swimming pools (5
public and 3 private). There were a further 8 deaths
among 21 to 40 year old males whilst free-diving for
the purposes of spear fishing in the ocean3.
PREVENTION STRATEGIES
CASE STUDY TWO
A 34 year old man drowned whilst trying
to hold his breath underwater in his
brother’s swimming pool on Australia
Day. The deceased was practising holding
his breath ahead of a scuba diving trip.
His family said he went underwater for a
third time that day and did not resurface.
His wife and brother dragged him from
the water and attempted CPR but it was
too late. “Both he and his brother would
always just like to have a competition
to see who could hold their breath the
longest. He could hold his breath for
about two minutes and fifty seconds” said
the deceased man’s wife.
CASE STUDY THREE:
An 18 year old male has drowned in a
public pool due to shallow water blackout.
The male was swimming laps of the pool
whilst holding his breath for the purposes
of training for underwater hockey. The
deceased had completed between 4 and
6 laps of the 50m pool underwater using
flippers and a face mask. The deceased
had swum two of the laps completely
underwater and decided to try swimming
another on a single breath without flippers.
There are a number of prevention strategies for
Shallow Water Blackout that have been proposed.
These include increasing awareness of the dangers
of hyperventilation, use of lifeguards to discourage
the practice at venues where they are located,
ensuring the practice of hyperventilation is not
part of any sport and where breath-holding is
undertaken appropriate medical and rescue
personnel, devices and procedures are in place.
23
FACT SHEET No.23
Shallow Water Blackout
THE ‘BREAK POINT’
SWB occurs because the normal, protective
‘breakpoints’ have not been triggered before
unconsciousness (due to cerebral hypoxia). There
are two chemical sensors in the body which detect
the levels of oxygen and carbon dioxide (CO2)
which protect us from a lack of oxygen. The CO2
sensor is the most sensitive. Hyperventilation i.e.
‘blowing off’ too much CO2 before submerging can
interfere with the sensor which is not triggered
early enough to prevent blackout6.
FURTHER INFORMATION:
Royal Life Saving Society - Australia
PO Box 558, Broadway NSW 2007
Q. What is Shallow Water Blackout?
A. The term ‘Shallow Water Blackout’ is commonly used to describe a loss of
consciousness under water caused by a lack of oxygen to the brain following
breath-holding. Although the term refers to ‘shallow water’, it can occur at any
depth. It occurs because the normal, protective “breakpoint” – the irresistible urge
to breath - has not been reached before consciousness is lost. The most common
cause is voluntary hyperventilation before submerging. Hyperventilation, or overbreathing, involves breathing faster and/or deeper than the body requires. There
are other less common causes, relating to heart abnormalities, which lead to loss
of consciousness in the water following hyperventilation.
Q. What is the “breakpoint”?
Victims of Shallow Water Blackout
should be treated as you would treat
any normal drowning victim, using
DRSABCD. See also Fact Sheet 4 –
Resuscitation.
Check for Danger to self,
to bystanders and to victim
(DANGER)
A. There are two chemical sensors in the body. These detect levels of oxygen
and of carbon dioxide (CO2) in the blood. These protect us from a lack of
oxygen. The CO2 sensor is the most sensitive; and when CO2 rises to a critical
point the breakpoint is reached first. Normally, when a swimmer is trying to
stay underwater for as long as possible, the “breakpoint” forces the swimmer
to surface and take a breath. If a person is submerged and the “breakpoint” is
reached whilst the mouth and nose are still underwater, the irresistible urge to
take a breath occurs, and water is inhaled into the lungs.
Shout “Are you ok?” and
gently squeeze the victim’s
shoulder (RESPONSE)
Q. Why is hyperventilating prior to underwater swimming, or a dive, dangerous?
Look, listen and feel for breathing
(BREATHING)
A. If the swimmer “blows off” too much carbon dioxide before submerging, it
will take longer for the carbon dioxide sensor to force the “breakpoint”. This
prolonged period may not occur before the oxygen sensor comes into play and
the drowning person may lose consciousness underwater.
Q. How common is Shallow Water Blackout?
A. Every year, several Australians drown from Shallow Water Blackout due to
hyperventilating before they submerge. Drownings have been recorded whilst
free diving in the ocean; and at public pools where people train for sports such
as underwater hockey or synchronised swimming. There are recorded cases
of children or young people hyperventilating or trying to swim long distances
underwater and then drowning, even in home swimming pools.
References
Checklist:
Send for help (SEND)
Clear and maintain airway
(AIRWAY)
If no signs of life, commence CPR
(COMPRESSION)
If available, grab a defibrillator
and follow the prompts
(DEFIBRILLATION)
Q. Is it dangerous?
A. Shallow Water Blackout is extremely dangerous. Medical science has
not yet established how many breaths it is safe to take prior to attempting
endurance underwater swimming. Royal Life Saving condemns the practice of
hyperventilation before participating in prolonged underwater swimming.
Q. Is all breath holding dangerous?
A. No. Simply holding one’s breath whilst swimming underwater is not
dangerous in and of itself. When the carbon dioxide “breakpoint” is reached,
the swimmer cannot resist coming to the surface to breathe, and normal oxygen
levels result. Breath-holding itself, without hyperventilating, is a completely
normal practice and in itself carries limited risk.
NEVER HYPERVENTILATE
BEFORE ENJOYING
UNDERWATER
AQUATIC ACTIVITIES
Proudly Supported by
ROYAL LIFE SAVING HAS DEVELOPED A NUMBER OF
FACT SHEETS ON WATER SAFETY ISSUES IN AUSTRALIA.
Contact Royal Life Saving on: 1300 737 763
or download them from:
www.keepwatch.com.au
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Phone: +61 2 8217 3100 Fax: +61 2 8217 3199
Email:[email protected]
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1. Gold Coast Bulletin. Gold Coast teenager Sam Brown’s freediving death exposes
dangers of the sport. News.com.au 2015 09-03-2015.
2. Gold Coast Bulletin. Brisbane husband and father Seth Beckman died on Australia
Day holding his breath under water. News.com.au 2015 19/02/2015.
3. Royal Life Saving Society - Australia. Royal Life Saving National Fatal Drowning
Database Sydney, 2002/03 to 2013/14.
4. Pearn J. Beneath the Surface: Medical imaging, radiotherapy, nuclear medicine and
children’s healthcare. A Queensland chronology: Amphion Press, 2014:33.
5. International Life Saving Federation. Medical Position Statement MPS 16 - Shallow
Water Blackout: International Life Saving Federation, 2011.
6. Royal Life Saving Society - Australia. Hypoxic Blackout. Aquatic and Recreation,
2004:32-33.
7. Wilmshurst P. ABC of oxygen: Diving and oxygen. British Medical Journal,
1998(317):996-99.
8. Pacific DANA. Breath-holding Blackout - Information Poster. In: Pacific DANA,
editor, 2014.
9. Royal Life Saving Society - Australia. Fact Sheet 23 - Shallow Water Blackout In:
Royal Life Saving Society - Australia, 2014.
www.royallifesaving.com.au