Shallow Water Blackout (SWB) can occur without warning and even the best swimmers are not spared should it be allowed to strike. Unlike what the name suggests, SWB does not only occur in shallow waters. In fact, it can happen in any body of water and it is difficult for the lifeguards to detect a victim of SWB due to its swift and sudden nature. The only way to prevent SWB from happening is to increase awareness of this little known killer.
SWB is due to hypoxia, which means low oxygen (O2) levels, to the brain. When one is breathing normally, the need to breathe is triggered by an increase in carbon dioxide (CO2) levels. The point at which breathing is triggered is indicated by the dotted line in the figures below. As seen in Figure 1 below, after breathing is triggered, the breathing action that takes place increases the O2 levels and lowers the CO2 levels.
Figure 1: O2 and CO2 levels during normal breathing (Source: Wikimedia Commons)
In contrast, when a swimmer hyperventilates, his/her CO2 levels are at a reduced level. As seen in Figure 2, the O2 levels will enter the blackout zone before the need to breathe is triggered. After the swimmer blacks out and the CO2 levels continue to rise, his/her body will naturally take in a breath. The unconscious swimmer will then take in a lungful of water and drown.
Figure 2: O2 and CO2 levels when hyperventilating (Source: Wikimedia Commons)
Prevention of SWB
Firstly, SWB can be prevented by educating swimmers of the dangers of breath holding. While hypoxic training is practiced worldwide, swimmers should be discouraged from performing such training on their own. Recreational swimmers should also avoid engaging in breath holding for fun.
Next, in the event that breath holding exercises are necessary during training, they should be performed under close supervision of a swimming coach. The swimming coach should then take necessary precautions to ensure the safety of the swimmers under his/her guidance.
Lastly, lifeguards on duty do have the responsibility to perform patrols periodically. This is to ensure that all blind spots are covered in the event of a swimmer in trouble being submerged in such areas.
Hopefully, by raising awareness of this silent killer, unnecessary loss of lives can be prevented.