Fainting

Alternative Name : Syncope

Definition:
.Fainting is a temporary loss of consciousness due to a drop in blood flow to the brain. The episode is brief (lasting less than a couple of minutes) and is followed by rapid and complete recovery. You may feel light-headed or dizzy before fainting.

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Fainting  is  a sudden, usually temporary, loss of consciousness generally caused by insufficient oxygen in the brain either through cerebral hypoxia or through hypotension, but possibly for other reasons. A pre- or near-syncope is diagnosed if the individual can remember events during the loss of consciousness (i.e., reports remembering dizziness, blurred vision, and muscle weakness, and the fall previous to hitting his or her head and losing consciousness). As loss of consciousness is a symptom for a variety of conditions and syncope is difficult to rule out outside of a hospital, a thorough examination is required in order to determine the cause, including interviews with witnesses as well as evaluation with an electrocardiogram. If the individual remembers feeling dizzy and loss of vision, but not the fall, then it is considered a syncoptic episode. Typical symptoms progress through dizziness, clamminess of the skin, a dimming of vision or greyout, possibly tinnitus, complete loss of vision, weakness of limbs to physical collapse. These symptoms falling short of complete collapse, or a fall down, may be referred to as a syncoptic episode. A breathing gas containing less than 16% oxygen can still contain enough to prevent hypoxia. On the other hand, mountaineers, pilots, and astronauts breathe oxygen-enriched gas because the partial pressure of oxygen in normal air mixture is not enough to prevent hypoxia, since the total pressure is reduced at high altitude. Syncope due to hypoxia can also occur because the lungs are not working properly, because a person is not breathing, because the blood is not circulating, or because the blood’s ability to transport oxygen is destroyed or blocked, e.g., by carbon monoxide, which, if present, binds itself to the blood’s hemoglobin.

The most common is a vasovagal attack, where overstimulation of a major nerve (called the vagus) slows the heart rate and lowers blood pressure. This overstimulation may be caused by intense stress, fear, pain or anything that suddenly increases pressure inside the body, such as blowing a trumpet.

Fainting may also result from low blood pressure (hypotension), often when someone stands up suddenly or is dehydrated and low in body fluids.

More rarely, fainting is due to abnormalities of the heartbeat.

A longer, deeper state of unconsciousness is often called a coma.
Anyone may be affected by fainting, but people who are unwell or dehydrated are at greater risk. Fainting – or feeling faint – is also common in pregnancy.

Symptoms:-
The person may start to feel light-headed, dizzy, nauseous and sweaty. They may have ringing in their ears and feel weak. Some people, however, have little or no warning symptoms.

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They then collapse to the ground and are unconscious for a few moments before coming round. They may feel woozy or nauseous for a little while afterwards and may vomit.

Causes:-
Central nervous system ischaemiaThe central ischaemic response is triggered by an insufficient level of oxygenated blood in the brain.

The respiratory system may contribute to oxygen levels through hyperventilation, though a sudden ischaemic episode may also proceed faster than the respiratory system can respond. These processes cause the typical symptoms of fainting: pale skin, rapid breathing, nausea and weakness of the limbs, particularly of the legs. If the ischaemia is intense or prolonged, limb weakness progresses to collapse. An individual with very little skin pigmentation may appear to have all color drained from his or her face at the onset of an episode. This effect combined with the following collapse can make a strong and dramatic impression on bystanders.

The weakness of the legs causes most sufferers to sit or lie down if there is time to do so. This may avert a complete collapse, but whether the sufferer sits down or falls down the result of an ischaemic episode is a posture in which less blood pressure is required to achieve adequate blood flow. It is unclear whether this is a mechanism evolved in response to the circulatory difficulties of human bipedalism or merely a serendipitous result of a pre-existing circulatory response.

Vertebro-basilar arterial disease
Arterial disease in the upper spinal cord, or lower brain, causes syncope if there is a reduction in blood supply, which may occur with extending the neck or after drugs to lower blood pressure.

VasovagalMain article: Vasovagal syncope
Vasovagal (situational) syncope—one of the most common types—may occur in scary, embarrassing or uneasy situations, or during blood drawing, coughing, urination or defecation. Other types include postural syncope (caused by a changing in body posture), cardiac syncope (due to heart-related conditions), and neurological syncope (due to neurological conditions). There are many other causes of syncope, including low blood-sugar levels and lung disease such as emphysema and a pulmonary embolus. The cause of the fainting can be determined by a doctor using a complete history, physical, and various diagnostic tests.

The vasovagal type can be considered in two forms:

Isolated episodes of loss of consciousness, unheralded by any warning symptoms for more than a few moments. These tend to occur in the adolescent age group, and may be associated with fasting, exercise, abdominal straining, or circumstances promoting vaso-dilation (e.g., heat, alcohol). The subject is invariably upright. The tilt-table test, if performed, is generally negative.
Recurrent syncope with complex associated symptoms. This is so-called Neurally Mediated Syncope (NMS). It is associated with any of the following: preceding or succeeding sleepiness, preceding visual disturbance (“spots before the eyes”), sweating, light-headedness. The subject is usually but not always upright. The tilt-table test, if performed, is generally positive.
A pattern of background factors contributes to the attacks. There is typically an unsuspected relatively low blood volume, for instance, from taking a low-salt diet in the absence of any salt-retaining tendency. Heat causes vaso-dilatation and worsens the effect of the relatively insufficient blood volume. That sets the scene, but the next stage is the adrenergic response. If there is underlying fear or anxiety (e.g., social circumstances), or acute fear (e.g., acute threat, needle phobia), the vaso-motor centre demands an increased pumping action by the heart (flight or fight response). This is set in motion via the adrenergic (sympathetic) outflow from the brain, but the heart is unable to meet requirement because of the low blood volume, or decreased return. The high (ineffective) sympathetic activity is always modulated by vagal outflow, in these cases leading to excessive slowing of heart rate. The abnormality lies in this excessive vagal response. The tilt-table test typically evokes the attack.

Much of this pathway was discovered in animal experiments by Bezold (Vienna) in the 1860s. In animals, it may represent a defence mechanism when confronted by danger (“playing possum”). This reflex occurs in only some people and may be similar to that described in other animals.

The mechanism described here suggests that a practical way to prevent attacks would be, what might seem to be counterintuitive, to block the adrenergic signal with a beta-blocker. A simpler plan might be to explain the mechanism, discuss causes of fear, and optimise salt as well as water intake.

Deglutition syncope
Syncope may occur during deglutition. Manisty et al. note: “Deglutition syncope is characterised by loss of consciousness on swallowing; it has been associated not only with ingestion of solid food, but also with carbonated and ice-cold beverages, and even belching.”

CardiacCardiac arrhythmias
Most common cause of cardiac syncope. Two major groups of arrhythmias are bradycardia and tachycardia. Bradycardia can be caused by heart blocks. Tachycardias include SVT (supraventricular tachycardia) and VT (ventricular tachycardia). SVT does not cause syncope except in Wolff-Parkinson-White syndrome. Ventricular tachycardia originate in the ventricles. VT causes syncope and can result in sudden death. Ventricular tachycardia, which describes a heart rate of over 100 beats per minute with at least three irregular heartbeats as a sequence of consecutive premature beats, can degenerate into ventricular fibrillation, which requires DC cardioversion.

Obstructive cardiac lesion
Aortic stenosis and mitral stenosis are the most common examples. Aortic stenosis presents with repeated episodes of syncope. Pulmonary embolism can cause obstructed blood vessels. High blood pressure in the arteries supplying the lungs (pulmonary artery hypertension) can occur during pulmonary embolism. Rarely, cardiac tumors such as atrial myxomas can also lead to syncope.

Structural cardiopulmonary disease
These are relatively infrequent causes of faints. The most common cause in this category is fainting associated with an acute myocardial infarction or ischemic event. The faint in this case is primarily caused by an abnormal nervous system reaction similar to the reflex faints. In general, faints caused by structural disease of the heart or blood vessels are particularly important to recognize, as they are warning of potentially life-threatening conditions. Among other conditions prone to trigger syncope (by either hemodynamic compromise or by a neural reflex mechanism, or both), some of the most important are hypertrophic cardiomyopathy, acute aortic dissection, pericardial tamponade, pulmonary embolism, aortic stenosis, and pulmonary hypertension.

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Other cardiac causes
Sick sinus syndrome, a sinus node dysfunction, causing alternating bradycardia and tachycardia. Often there is a long pause asystole between heartbeat.

Adams-Stokes syndrome is a cardiac syncope which may occur with seizures caused by complete or incomplete heart block. Symptoms include deep and fast respiration, weak and slow pulse and respiratory pauses that may last for 60 seconds.

Aortic dissection (a tear in the aorta) and cardiomyopathy can also result in syncope.

Other causesFactors that influence fainting are fasting long hours, taking in too little food and fluids, low blood pressure, hypoglycemia, growth spurts, physical exercise in excess of the energy reserve of the body, emotional distress, and lack of sleep. Orthostatic hypotension caused by standing up too quickly or being in a very hot room can also cause fainting.

More serious causes of fainting include cardiac (heart-related) conditions such as an abnormal heart rhythm (an arrhythmia), wherein the heart beats too slowly, too rapidly, or too irregularly to pump enough blood to the brain. Some arrhythmias can be life-threatening. Other important cardio-vascular conditions that can be manifested by syncope include subclavian steal syndrome and aortic stenosis.

Orthostatic (postural) hypotensive faints are as common or perhaps even more common than vasovagal syncope. Orthostatic faints are most often associated with movement from lying or sitting to a standing position. Apparently healthy individuals may experience minor symptoms (“lightheadedness”, “greying-out”) as they stand up if blood pressure is slow to respond to the stress of upright posture. If the blood pressure is not adequately maintained during standing, faints may develop. However, the resulting “transient orthostatic hypotension” does not necessarily signal any serious underlying disease. The most susceptible individuals are elderly frail individuals, or persons who are dehydrated from hot environments or inadequate fluid intake. More serious orthostatic hypotension is often the result of certain commonly prescribed medications such as diuretics, ?-adrenergic blockers, other anti-hypertensives (including vasodilators), and nitroglycerin. In a small percentage of cases, the cause of orthostatic hypotensive faints is structural damage to the autonomic nervous system due to systemic diseases (e.g., amyloidosis or diabetes) or in neurological diseases (e.g., Parkinson’s disease).

Fainting may occur while you are urinating, having a bowel movement (especially if straining), coughing very hard, or when you have been standing in one place too long. Fainting can also be related to fear, severe pain, or emotional distress.

A sudden drop in blood pressure can cause you to faint. Your blood pressure may drop suddenly if you are bleeding or severely dehydrated. It can also happen if you stand up very suddenly from a lying position.

Certain medications may lead to fainting by causing a drop in your blood pressure or for another reason. Common drugs that contribute to fainting include those used for anxiety, high blood pressure, nasal congestion, and allergies.

Other reasons you may faint include hyperventilation, drug or alcohol use, and low blood sugar.

Less common but more serious reasons for fainting include heart disease (such as abnormal heart rhythm or heart attack) and stroke. These conditions are more likely in persons over age 65 and less likely in those younger than 40.

Other causes:
Factors that influence fainting are fasting long hours, taking in too little food and fluids, low blood pressure, hypoglycemia, growth spurts,[citation needed] physical exercise in excess of the energy reserve of the body, emotional distress, and lack of sleep. Orthostatic hypotension caused by standing up too quickly or being in a very hot room can also cause fainting.

More serious causes of fainting include cardiac (heart-related) conditions such as an abnormal heart rhythm (an arrhythmia), wherein the heart beats too slowly, too rapidly, or too irregularly to pump enough blood to the brain. Some arrhythmias can be life-threatening. Other important cardio-vascular conditions that can be manifested by syncope include subclavian steal syndrome and aortic stenosis.

Diagnosis:
Clinical testsIf one is suffering from syncope, there are many underlying causes that may be contributing to the episodes. It is important to understand that there is no master list of tests that are currently being used to diagnose the underlying cause(s). However, there are some common diagnostic tests for fainting.

A hemoglobin count may indicate anemia or blood loss. However, this has been shown to be useful in only about 5% of patients being evaluated for fainting.[4]

An electrocardiogram (ECG) records the electrical activity of the heart. It is estimated that from 20%-50% of patients will have an abnormal ECG. However, while an ECG may identify conditions such as atrial fibrillation, heart block, or a new or old heart attack, it typically does not provide a definite diagnosis for the underlying cause for fainting.

Sometimes, a Holter monitor may be used. This is a portable ECG device that can record the wearer’s heart rhythms during daily activities over an extended period of time. Since fainting usually does not occur upon command, a Holter monitor can provide a better understanding of the heart’s activity during fainting episodes.

The Tilt table test is performed to elicit orthostatic syncope secondary to autonomic dysfunction (neurogenic).

For patients with more than two episodes of syncope and no diagnosis on “routine testing”, an insertable cardiac monitor might be used. It lasts 14 to 18 months. Smaller than a pack of gum, it is inserted just beneath the skin in the upper chest area. The procedure typically takes 15 to 20 minutes. Once inserted, the device continuously monitors the rate and rhythm of the heart. Upon waking from a “fainting” spell, the patient places a hand held pager size device called an Activator over the implanted device and simply presses a button. This information is stored and retrieved by their physician.

San Francisco syncope rule:
The San Francisco syncope rule was developed to isolate patients who have higher risk for a serious cause of syncope. Anyone with high risk criteria needs to be further investigated. They are summed up by the CHESS mnemonic: congestive heart failure, hematocrit <30%, electrocardiogram abnormality, shortness of breath, or systolic blood pressure <90 mm Hg

Treatment :
Recommended treatment involves returning blood to the brain by positioning the person on the ground, with legs slightly elevated or leaning forward and the head between the knees for at least 10-15 minutes, preferably in a cool and quiet place. As the dizziness and the momentary blindness passes, the person may experience a brief period of visual disturbances in the form of phosphenes, sudden sore throat, nausea, and general shakiness. For individuals who have problems with chronic fainting spells, therapy should focus on recognizing the triggers and learning techniques to keep from fainting. At the appearance of warning signs such as lightheadedness, nausea, or cold and clammy skin, counter-pressure maneuvers that involve gripping fingers into a fist, tensing the arms, and crossing the legs or squeezing the thighs together can be used to ward off a fainting spell. After the symptoms have passed, sleep is recommended. If fainting spells occur often without a triggering event, syncope may be a sign of an underlying heart disease.

Disclaimer: This information is not meant to be a substitute for professional medical advise or help. It is always best to consult with a Physician about serious health concerns. This information is in no way intended to diagnose or prescribe remedies.This is purely for educational purpose.

Resources:

http://en.wikipedia.org/wiki/Syncope_(medicine)

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