Fainting is a temporary loss of consciousness caused by reduced blood flow and oxygen to the brain. Fainting, or “passing out”, can occur in otherwise healthy people, or it may indicate serious underlying disease that requires treatment. Many things can cause a person to faint, including epilepsy, internal bleeding, head injuries, low blood pressure, and low blood sugar associated with diabetes medications. This article focuses on fainting that is caused by reduced blood flow to the brain.
Fainting can occur with or without warning, and may result in injuries. Between 16% and 35% of people who faint injure themselves when they fall. Most injuries are minor, such as cuts and bruises, but bone fractures and serious injuries from automobile or industrial accidents also occur after episodes of fainting.
Fainting is common in the US, accounting for approximately 3% of emergency room visits and up to 6% of hospitalizations each year. Approximately half of the US population will experience one episode of fainting sometime during their lives. For most people, fainting is an isolated event, but about one-third of people who faint experience recurring episodes.
Fainting can be caused by any condition that results in reduced blood flow to the brain. As such, fainting has many potential causes, and determining which one is responsible can be a challenge. Many causes of fainting, especially in young people, are relatively harmless. However, others causes, such as heart disease, can be life-threatening if left untreated. Accurate diagnosis is essential to determine a patient’s risk and course of treatment.
Heart disease is one of the most serious causes of fainting. Abnormal heart rate or irregular heart rhythm (arrhythmia) can reduce the efficiency of the circulatory system, and result in a sudden drop in blood flow to the brain. People who faint as a result of these heart conditions tend to be older than 65 years of age.
Other cardiac conditions that cause fainting, such as pulmonary embolism or a blocked artery, lower the blood pressure or disrupt blood flow to the brain. Fainting resulting from these causes often occurs during or after exercise, and affects young people (especially athletes) as well as older adults.
One relatively harmless form of fainting is caused by a nervous system response that reduces blood pressure and blood flow to the brain. This type of fainting usually occurs while a person is standing, and is often triggered by fear, stress, or pain. It may recur in specific situations such as urinating, defecating, or coughing.
This type of fainting occurs most often in children and young adults, but it may occur at any age. It typically occurs after two or three minutes of symptoms such as a sensation of warmth, nausea, lightheadedness, dizziness, blurred or faded vision, or stomach upset. If the person reclines, restoring the blood flow, he or she can recover within a few minutes.
Other things can cause a person to “pass out” that are not covered in this article. Epilepsy, internal bleeding, head injuries, low blood pressure, and low blood sugar associated with diabetes medications can all cause a loss of consciousness. This article, however, focuses on fainting caused by a reaction to stress or underlying heart disease.
The symptoms that precede blood flow—related fainting depend on the underlying cause. People who faint as a reaction to stress or fear often describe a preceding sense of warmth, nausea, upset stomach, or a cold sweat.
People whose fainting is a result of heart disease experience palpitations, shortness of breath, constriction, or pressure in the chest before fainting.
The timing of symptoms that precede fainting is determined by the underlying cause. When fainting is brought on by stress or fear, the symptoms usually last a few minutes before loss of consciousness. When underlying heart disease is responsible, symptoms usually occur only a few seconds before loss of consciousness.
Your doctor will ask you for an accurate medical history, including a detailed description of the symptoms, associated circumstances, and timing of each episode of fainting. Your physician will also ask you about any activities and possible triggers that occur with your episodes of fainting. Triggers include strong emotions such as fear or anxiety, fatigue, sleep deprivation, hunger, pain, excessive heat, and alcohol consumption.
Activities you may have been performing directly before fainting, such as exercise, coughing, urinating, or standing up quickly, will provide clues about the underlying cause. Similarly, the position you were in before fainting (e.g., standing up, lying down) is also important in identifying causes.
If possible, have a witness describe your fainting episode to your doctor. Simple fainting is often difficult to distinguish from a more serious disorder such as epilepsy. How long a person is unconscious and whether or not the person is confused about his or her surroundings after regaining consciousness are key factors used to distinguish between fainting and seizures. It is valuable, then, to bring someone with you who has witnessed your fainting episodes when you seek treatment.
Your physician will ask you about medications that you are currently using—especially medications you may be taking for heart conditions. Many medications cause changes in blood pressure or heart rhythm that can result in fainting. These medications include drugs that lower blood pressure (e.g., antihypertensive agents, diuretics, nitrates), drugs that affect heart output (e.g., beta-blockers, digitalis), drugs that affect the normal heart rhythm (e.g., tricyclic antidepressants, phenothiazines, quinidine, amiodarone), and drugs that alter consciousness (e.g., alcohol or cocaine).
Your physician will also ask questions about your personal or family history of heart disease. People whose fainting is related to heart attacks, heart rhythm abnormalities, structural defects in the heart, or other cardiac diseases have a less favorable prognosis than people whose fainting is not related to heart disease.
After completing the medical history, your physician will perform a comprehensive physical examination. This examination will include taking your vital signs (e.g., blood pressure, pulse, temperature, etc.) both reclining and standing up to identify possible differences in blood pressure that could cause fainting. A fever may indicate that an infection such as a low-grade urinary tract infection or pneumonia may be triggering the fainting. Your physician will also look for any signs of trauma (including head injuries, lacerations, or fractures) that may have led to or resulted from your fainting.
You may be asked to provide a stool sample to identify or rule out the possibility of internal bleeding. You will be asked to provide a blood sample to evaluate your blood sugar level. If you are diabetic, this test will help determine whether your fainting is associated with diabetes medication.
If your physician suspects that your fainting is related to blockage of the carotid artery in your neck, he or she may massage the artery to determine whether that causes you to faint.
The physical examination will focus on your heart function. Your physician will listen carefully for irregular heart rhythms as well as any other sounds that suggest heart murmurs or other defects in your heart valves. Your physician will also examine you for any signs or symptoms of congestive heart failure.
Your physician will also perform a detailed neurological examination. This examination will include looking for confusion, abnormal behavior, headache, fatigue, and sleepiness. Your reflexes, sensory response, and coordination will be evaluated to identify or rule out neurologic disease that may be causing the fainting.
Depending on whether your history and physical examination suggest heart disease, your physician may order an electrocardiogram (ECG). An ECG is a test that records your heart rate and rhythm. Patches with wires attached are placed on your chest and connected to a monitor and a recorder. Irregularities in your heart rhythm that may be causing your fainting can be identified using this test. If irregularities are identified, additional diagnostic tests may be done to confirm and localize the cause.
If your ECG and other tests are inconclusive, you may be asked to wear a heart monitor.
Your physician may perform a tilt-table test. A tilt-table test is designed to simulate the conditions that cause a person to faint. It allows a physician to evaluate how blood pressure, heart rate, and heart rhythm respond to a change in position from lying down to standing. In the test, the patient is positioned on a table, and the table is tilted upwards for 20 to 45 minutes. The test is based on the premise that in susceptible persons, the decrease in blood flow back to the heart from the extremities triggers fainting. If the patient does faint during the test, the heart monitor should show whether or not the episode was caused by an abnormal heart rhythm.
If after all these tests, the cause of your fainting is still unclear, your physician may order additional tests to evaluate your heart and neurological function. These tests may include an electrophysiology study (EPS), in which catheters are threaded into the heart to record the heart’s electrical impulses, and to assess the response of the heart to externally supplied electrical pacing and beats. Other tests include an electroencephalograms(EEG), magnetic resonance imaging (MRI), echocardiogram, and psychiatric evaluation, depending on the suspected cause of the fainting.
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