Shallow Water Blackout and Near Drowning

One of the saddest recoveries I had twenty years ago, when I was on the sheriff’s office dive team, was of a young man about five miles off Marco Island. He had gone out with two friends for a day of fishing. He bet his buddies he could dive down and touch the bottom, about 35’ of water. He donned a mask and fins and dove down, never to surface. 911 was called, and when we arrived, we found him at the bottom below the boat. It was determined he had died from shallow water blackout. When I teach a first aid class, as we are a boating community, I will bring up both shallow water blackout as well as the near-drowning experience; more on that later. With shallow water blackout, trained freedivers use the technique of hyperventilation (rapid breaths) to flush carbon dioxide levels in the bloodstream. This causes hypocapnia, which is a delay in the need to breathe. Trained freedivers have safety systems in place to deal with someone passing out as they complete their freedive. Okay, what the heck am I talking about? It’s simply this: when someone holds onto the side of your boat and takes multiple rapid breaths in some mistaken belief they are getting more than the 21% oxygen in our air, there is a good chance, depending on how deep they go, that they are going to die. See, when someone does this, they indeed can trick their body into letting them stay down longer by delaying the brain in telling the body to BREATHE! But here’s the problem: SCUBA divers understand water pressure and Boyle's law. When a freediver descends, the pressure surrounding them increases, causing the volume of the lungs and other gas-filled spaces in the body to increase proportionally. This pressure change affects the partial pressure of gases within the lungs, particularly oxygen and carbon dioxide, which can contribute to the onset of shallow water blackout. All you need to know is that as someone dives deeper, they burn the oxygen in their body at a faster rate. As they come back up to a shallow depth, the oxygen in their body drops below the level that they can stay awake - hypoxemia. They pass out just below the surface, sink to the bottom, and drown. So, as a boater, what should you do? It’s simple. If someone wants to dive down below your boat, and assuming they know how to use snorkel gear, a mask, and fins, you need to watch what they are doing. If they take one nice big breath and hold it, they have not flushed carbon dioxide out of their lungs. BUT if someone is hanging on the side of your boat, rapidly breathing (hyperventilating) in a mistaken belief they are going to get extra mystery oxygen, you have to tell them that unless they stop there is a good chance they are going to die. Which brings us to near-drowning. Near drowning is a common phrase for surviving a drowning event. The example I use in my classes is when someone is found at the bottom of a pool, very often a child, and is brought to the surface and revived. But first, let’s look at drowning itself. Public Safety Divers are trained to recognize two types of drowning victims: active drowning victims and passive drowning victims. What you see normally on TV and in movies is the active drowning victim, actors yelling for help. BUT what you need to recognize is that an active drowning victim is gasping for air and barely taking in enough air to breathe. They will NOT normally call for help. An active drowning victim will have his or her arms extended out to the side, trying to push down and be vertical in the water. If you see someone who appears to be struggling in the water, it could look like someone treading water, yell to them and ask if they are okay. An active drowning victim will find it hard to have a conversation, and if that’s the case, you need to act quickly and safely to attempt to rescue that person. A passive drowning victim is obvious; they will not be moving. A secondary issue is occurring, a heart attack, stroke, seizure, or a head injury would be some of the causes. In any case, quick removal from the water and aggressive first aid like mouth-to-mouth resuscitation are paramount in importance. A person who is drowning becomes an ineffectual swimmer and sinks underwater. The victim will hold their breath for a short period of time until unconsciousness occurs. The breathing reflex will trigger the airway to close when water touches it as the victim swallows water. This can go on for some time, water is swallowed, and only small amounts are introduced into the lungs. When a rescue is made in a short period of time, the chance of recovery is greatly increased. After four to five minutes underwater, the victims’ brain oxygen supply drops, and underwater breathing will begin. Water is now going into the lungs.

Assuming a recovery was made, we were able to pull that child out of the pool and revive him or her. He or she is seemingly okay, alert, crying, and hugging mom and dad. Guess the show's over; we are all heroes, right? Nope. You need to know, and you need to communicate to all present, especially Mom and Dad, that even a little water in the lungs can cause serious health problems in the next few hours. The simple explanation is that when the victim aspirates even small amounts of water into their lungs, water that bypasses the gag reflex, it causes different health issues depending on the type of water. Fresh water (pools) dilutes the normal body salts found in the body. This dilution directly damages the blood cells of the pulmonary membranes, the alveoli, and may cause them to rupture. Salt water (Gulf) is two to three times more concentrated in salt than the normal body fluids. Because of this difference, your body pulls water out of body tissues and into the lungs to dilute the salt. Basically, you start to drown yourself. All you really need to know is if someone is pulled from the water and is unconscious, unable to breathe, gasping for air, coughing, or just having trouble breathing, they need immediate medical attention. The safe thing to do is to ALWAYS call 911 for any suspected or real medical emergency, no matter how insignificant it seems at the time. So now you know what to look for and how to react and speak out regarding shallow water blackout and near drowning! Go be a sheepdog and save a life!