Shallow Water Blackout & Secondary Drowning

Amy Peden

National Manager – Research and Policy, Royal Life Saving Society – Australia and

Associate Professor Richard Franklin, James Cook University and Royal Life Saving Society – Australia

Drowning in Australia

• 292 people on average drowned in Australia each year for the past 10 years

• The 2014 Royal Life Saving National Drowning Database found that 266 people drowned in 2013/14

• 81% of all drowning victims were male

Drowning in Australia 2013/14

• Largest number of drowning deaths occur in rivers, creeks and streams

• Swimming pools overtook beaches as the second leading location for drowning

Drowning in Australia 2013/14

• There are a diverse range of activities being undertaken prior to drowning in Australia

Drowning Defined

• “Drowning is the process of experiencing respiratory impairment from submersion/immersion in liquid.”

• Drowning outcomes should be classified as: death, morbidity, and no morbidity.

• There was also consensus that the terms wet, dry, active, passive, silent, and secondary drowning should no longer be used.

The Physiology of Drowning

• Mouth, nose submerged• Aspiration • Breath hold • Cold shock• Diving response • Autonomic conflict • Laryngospasm • Inhalation of Water• Ingestion • Cardiac Arrest

Shallow Water Blackout – How does it happen? • Shallow Water Blackout (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) & 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 blackout.

Shallow Water Blackout – How does it happen?

The “Break Point”

Also Known As

• Shallow Water Blackout• Hypoxic Blackout• Underwater blackout• The Long dive• Long breath holding• Surface Blackout• Deep water blackout• Freediver blackout• Latent hypoxia

Why?

• 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.

Shallow Water Blackout

• There are challenges around quantifying the role of SWB in broader drowning fatalities

• Often the activity prior to drowning is unwitnessed so hard to know if the deceased was participating in breath-holding activities

• No autopsies to rule out other potential causes such as cardiac arrhythmias and seizure disorders (Long QT Syndrome)

Differential Diagnoses• 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” response.

Prevention Strategies

• A number of prevention strategies proposed. These include: – Increasing awareness of the dangers of

hyperventilation– Use of lifeguards & facility staff to discourage

the practice at venues – 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 must be in place.

Known deaths in Australia

• 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 complete in activities such

as underwater hockey or free-diving: most commonly in public pools

– Those recreating in home swimming pools and holding breath

Known deaths in Australia

• 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 ocean

SWB – Prevention Strategies

• Public awareness & public education through fact sheets

• Royal Life Saving Fact Sheet on ShallowWater Blackout

SWB Prevention Strategies

• Diver specificeducation

• Undertaken by DiversAlert Asia Pacific

Policies

Case Studies & Media Attention

• Recent media has highlighted the dangers related to activities involving breath-holding and pre-immersion hyperventilation:

• What follows are three real life cases from recent years

Case Study 1

Case Study 2

Case Study - 3An 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.

Long QT Syndrome

• What is it?

Long QT Syndrome

• Triggers• 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.

Secondary Drowning – A variety of terms• Secondary drowning• Dry drowning• Delayed drowning• Passive drowning

• Terms such as these should be discouraged • Please use the term drowning and add

appropriate outcome (e.g. fatal, non-fatal, morbidity, no morbidity)

Secondary drowning

• Secondary Drowning occurs when someone breaths in small amounts of water.

• This triggers the muscles in the airway to spasm and makes breathing difficult. Fluid builds up in the lungs and causes trouble breathing.

• What are the risks?• Secondary or dry drowning is not common,

and is estimated to account for 1-2% of drowning

Secondary drowning

• Prevention– Supervision is key, especially for

children and inexperienced swimmers– Restricting Access to water –

especially for children– Resuscitation

Acknowledgements

• Professor John Pearn• National Medical Advisor, Royal Life

Saving Society - Australia

Any questions?