Why do perfectly heathy people pass out sometimes?

How many of us have been in this situation? Its a beautiful June day and you're sitting in church while a happy couple is taking their vows. The groomsmen are lined up on one side and the bridesmaids on the other when one of the bridesmaids begins to wobble. Only seconds later her knees buckle and in an eyeblink she slumps to the floor. Across town a police officer is in his doctors office for a physical. The nurse comes in to the room. She preps his arm to draw some blood, inserts the needle, and "THUNK". She looks up to see him slumped against the wall his glazed eyes staring at the ceiling. Later that afternoon a carpenter is framing a house. He swings the hammer but hits his thumb instead of the nail he was aiming for. Its not the first time he's done this but today is different. Nerve cells carry the pain signal up to his brain as usual but this time an overwhelming sense of nausea sweeps over him, he breaks out in a cold sweat, his eyes go black, and down he goes.

Most of us have witnessed one of these situations either in real life or in the movies. They elicit laughs in the movies and gasps in real life. Those nearby run to help. They often try to prop the person up. They may also fan them and give them something to drink in and effort to revive them. Usually in the movies someone throws a pitcher of cold water on the persons face and they magically wake up spitting and gasping to audience laughter.

So what are these events? Why does someone pass out at a beautiful event like a wedding? Why does a cop who has seen far worse pass out when he sees a small needle in his arm? Why does a carpenter who has sustained more than his share of injuries in his career suddenly hit the ground just because he hit his thumb? What causes these things to happen and more importantly, are they dangerous?

The medical term for someone passing out is syncope. Although many things can cause syncope, the events I am describing above are a specific but very common situation called a vasovagal event or vasovagal syncope. In each case a part of the nervous system known as the parasympathetic nervous system has been activated. When that happens the heart rate slows down and the blood vessels dilate leading to a drop in blood pressure. If conditions are right these changes make it more difficult for the heart to pump blood to the highest point in our body. Since that is where the brain usually is, the brain doesn't receive enough blood and oxygen so it begins to shut down. This can lead to symptoms like nausea, lightheadedness, cold sweats, and disturbed vision. If the problem is not recognized and addressed quickly the decreased blood flow eventually causes complete loss of consciousness and the person passes out.

There are many things that can trigger a vasovagal event. Pain, Emotional upset, dehydration, warm stuffy rooms, and for some reason getting up to urinate in the middle of the night seems to be a trigger for some people. The odd thing is that many times the trigger is something that has happened before without causing loss of consciousness. Why do the triggers sometimes cause a person to pass out and other times have no effect at all? It may be that there needs to be a combination of factors which predispose the patient to the event for the trigger to set it off. Perhaps the person is a little dehydrated. Maybe they have a viral infection. Perhaps they skipped breakfast or didn't get enough sleep the night before. It may be any one of these things or a combination of them. There may be factors we aren't even aware of that put the body in a condition where the trigger is just the final straw that causes the lights to go out.

Its not really clear why the nervous system reacts in such a way as to cause our heart to slow and our blood pressure to drop or what advantage it might provide, but fortunately the problem usually fixes itself. When the person loses consciousness they tend to slump or fall to the ground which means the head is lower down, blood flow is restored and consciousness returns. In most cases the person usually wakes up quickly. Loss of consciousness often lasts only a minute or two and frequently less. Unlike a stroke where there is a permanent complete loss of blood flow resulting in damage to brain tissue, vasovagal events only involve a very brief partial reduction in blood flow so there is generally no injury to the brain. For this reason vasovagal events are not considered to be dangerous as long as the person doesn't strike something after they pass out or fall from a high place when they lose consciousness.

The key to avoiding injury is recognizing the warning signs and taking steps to interrupt the event before loss of consciousness occurs. Most vasovagal events will be preceeded by some of the symptoms described above, nausea, cold sweats, darkening vision, dizziness, blurry vision, or spots in the vision. Some people describe a pounding in their ears prior to an event. The first event is usually difficult to prevent because the person has never had one before and they are caught entirely by surprise. Before they know what hit them they are on the floor.  The second event is usually much different because the moment the warning signs appear a lightbulb goes on that says "Hey this has happened before". Once that happens it becomes a race against time. If the person takes action in the next couple of seconds they can stop the event in its tracks but they have to know what to do.

So what do you do when you feel like you are about to go down or if you see someone else who is on the way down or already on the floor? Remember this is a blood flow problem. We need to increase blood flow to the upper body to reverse the effects of a vasovagal event. There are several ways we can do that.

What to do:

• Lay down on the floor. Sometimes people are too embarassed to lay down on the sidewalk or in public but you only have seconds. The time it takes to find a private place is often the difference between passing out and not. If you are afraid or embarassed to lay down you should consider what's more embarassing, laying on the floor voluntarily or crashing into it face first, because one or the other will definitely happen.
  
• Once on the floor raise the legs to increase blood flow to the upper body
• If there isn't enough room to lay down, bend over and put your head between your legs to get it as low as possible.
• Heat causes blood vessles to dilate and blood to pool in the extremities. Cold does just the opposite. Applying cold compresses to the body will constrict blood vessels in the arms and legs and push more blood towards the head. Opening a door or window to let cool breeze in can also help.
• Drinking cold liquids will also cause blood vessel constriction and help shift more blood flow to the head. Fluids will have the added benefit of treating dehydration if this is a contributing factor.

What not to do:

• Do not try to find a private place to lay down. You wont make it.
• Do not try to hold a person up when they are passing out. You will only prolong the time it takes to restore adequate blood flow to the brain and you will delay the recovery of consciousness.
• Do not pour cold water on the persons face. They will wake up quickly enough on their own. Pouring liquid on the face of someone who is unconscious runs the risk of having them inhale water into their lungs turning a minor self resolving issue into a potentially dangerous one.

Loss of consciousness is a scary thing and while vasovagal events are generally not dangerous there are other things that can cause someone to pass out which can be more serious. Strokes, seizures, cardiac arrest, and irregular heart rhythms can also lead to loss of conscousness and obviously require a more urgent approach.

If you witness someone who has passed out check their pulse and their breathing. If they have no pulse or they are not breathing begin CPR and call EMS.  If they have a pulse and are breathing on their own make sure their airway is clear, raise their legs, and give them a minute or two to wake up. If possible put a cold compress on their limbs and neck. If after a few minutes they do not wake up call an ambulance. If they do wake up resist the urge to help them to their feet right away. Give them a few minutes to recover. When they feel a little better help them to a sitting position. Once they are sitting,If available, give them something cold to drink. Wait 5 or 10 minutes at least and if they are feeling up to it help them to a standing position.

Any time someone loses consciosuness it should be reported to their physician. On rare occasions seizures and irregular heart rhythms can masquerade as something minor. Even if it seems like you have had a simple vasovagal event report it to your doctor so he or she can check you to rule out the possiblity of a more serious problem.