There have been a couple of recent reports of pilots fainting on board commercial aircraft. When most people faint, it is not usually a problem. When a pilot faints in flight, it could be catastrophic.
Fainting, or syncope in medical lingo, occurs when the brain does not get enough oxygenated blood to support neurological functioning. Basically, when the brain determines it is not getting enough blood, it says to the body “if you do not get me enough blood, I am going to make you get me enough by making you lie down!”
Fainting most commonly is due to blood pooling in the lower extremities and abdomen so the heart does not have enough blood returning to pump out to maintain blood pressure. This can happen when someone is told bad news, has their blood drawn, has severe pain, and many other reasons. This most common cause of fainting is called a vasovagal response. In these situations, the blood vessels in the peripheral vascular system (e.g. arms, legs, and abdomen) dilate due to stimulation from the vagus nerve which controls much of the automatic nervous system (the part of the nervous system we cannot actively control like heartbeat and blood pressure). The vessels dilate, the blood pools, blood pressure drops, and our brain does not like it.
Dehydration is one of the most common causes of syncope. Dehydration can be from just not drinking enough fluid (to avoid having to urinate in the aircraft), viral stomach illnesses which cause vomiting and diarrhea, to taking a diuretic for high blood pressure which increases fluid loss. Also remember that flying at higher altitudes or in pressurized aircraft causes more dehydration due to low humidity of those environments. Almost any medication which has the side effect of sedation may also contribute to fainting.
Pilots in cockpits are also prone to fainting due to the sitting position which presses on the veins in the back of the leg causing further reduction of blood return to the heart. Anemia or low blood cell count will also predispose to fainting as will advanced age.
When a person faints, they may exhibit jerking movements similar to those seen in seizures. Unfortunately, due to these movements, many people who faint are incorrectly labeled as having had a seizure which has serious implications for driving and flying.
There are other reasons beside vasovagal syncope which can cause fainting such as certain irregular rhythms of the heart, low blood sugar, and panic attacks with hyperventilation. Thus, many emergency room visits and even hospitalizations occur to evaluate a fainting event- particularly when it happens the first time- to search for a cause besides vasovagal syncope. Doctors call vasovagal syncope a diagnosis of exclusion because vasovagal is what we call it when we cannot find another reason.
When a person faints, the best thing to do is to lie them down and raise their feet. This promotes blood return to their heart and raises blood pressure to the brain. A cool wet towel to the face helps but slapping them silly like I once saw another physician do is uncalled-for. Save that ridiculous technique for bad movies. If a person does not wake up spontaneously within a minute or so after lying down, immediate medical attention should be sought.
Prevention of fainting is relatively easy: hydration, hydration, and more hydration. Also, eating something salty can help. Without some salt, you will not retain fluid so all hydration will be lost more quickly. If you have high blood pressure, you should not use salt, but if you do not have hypertension, a bag of potato chips can raise blood pressure slightly to help prevent fainting. (We often see patients, who do not have high blood pressure, develop problems from restricting salt too aggressively!)
When a pilot asked himself if he is fit to fly, one of the important things to consider is whether he is hydrated or has other issues that might make him more prone to fainting. In the two pilot cockpit of an airliner, fainting may be a non event. In a single pilot cockpit, it could be disastrous.
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