Pass the smelling salts.
Some experts estimate that about half of all people will pass out at least once in their lives, and the causes can be remarkably varied.
Fainting spells, which doctors call syncope (pronounced SINK-uh-pee), are common among people of all ages, said Dr. Leonard Ganz, director of cardiac electrophysiology at UPMC.
"It's a problem with a very wide spectrum," he said. "If the only time you ever pass out is when giving blood at a drive, then the solution is not to give blood. If on the other hand, you're passing out frequently without obvious triggers, it can be really disruptive and ruin your life."
Sixty percent of the time blackouts are caused by the "vasovagal reflex." That's what happens when someone faints while giving blood or receiving a shot.
As the needle-bearing nurse approaches, "the nerves that control the heart rate and the blood pressure send an inappropriate signal for the heart to slow down and the blood vessels to dilate so the blood pressure goes down," Ganz explained. "The final common pathway for passing out is there's not enough blood going to the brain to keep you conscious."
The vasovagal reflex also can kick in if a person has been vomiting, stands up too suddenly or stands for too long in a hot place. Medication can often help.
"Vasovagal syncope is almost always in the upright position," said Dr. Marc Itskowitz, an internist at Allegheny General Hospital, and so it is probably not a major factor in blackouts that occur behind the wheel.
"For someone to pass out while driving a car, I would be most concerned about a cardiac cause, such as an arrythmia, or a seizure," Itskowitz said.
About 20 percent of blackouts are caused by cardiac problems, such as abnormal rates and rhythms that are connected with problems in the electrical conduction of the heart. They can often be treated with a pacemaker.
Epilepsy is not a common reason for losing consciousness, the doctors said, but its seizures can sometimes be confused with syncope.
Seizures are caused by overactivity of neurons in the brain. Brain wave studies, such as the electroencephalogram, or EEG, as well as MRIs and other brain scans, can help identify a seizure disorder.
Another cause for a temporary loss of consciousness is low blood sugar, or hypoglycemia.
Sleep apnea, a condition that repeatedly wakes patients at night when their airways are blocked and too little oxygen reaches the brain, can lead to daytime drowsiness, which may cause a person to fall asleep at the wheel.
The vasovagal reflex and heart problems are among the 30 or 40 different causes of losing consciousness, Itskowitz said, but 20 percent of the time doctors fail to find any cause.
It's important that patients get a good medical examination after fainting episodes.
The assessment begins with a medical history that pays particular attention to previous cardiac problems or seizures followed by a physical exam. Itskowitz said doctors also typically do an electrocardiogram, or EKG, to check for heart rhythm problems.
Another common exam is the tilt-table test, in which the patient is strapped to a bed and tilted, head up, at a 70-degree angle. That can help show whether a person is likely to faint from the vasovagal reflex when his posture changes.
Patients may also be asked to wear a portable, external EKG machine for a period of time to record their heart rhythms for later review, but syncope episodes may be so sporadic that the monitor doesn't catch one.
To overcome that problem, doctors are using a new implantable loop recorder, an eraser-sized device that is placed under the chest skin in a 20-minute office procedure. Its batteries last more than 15 months, and it can be programmed to keep a record of heart rhythms that are either too slow or too fast.
Anita Srikameswaran can be reached at anitas@post-gazette.com or 412-263-3858.
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