Merck manual fainting

Rather, the reaction is caused directly by the substance. Iodine-containing substances that can be seen on x-rays radiopaque contrast agents Radiopaque Contrast Agents During imaging tests, contrast agents may be used to distinguish one tissue or structure from its surroundings or to provide greater detail.

Contrast agents include Radiopaque contrast agents Monoclonal antibodies manufactured antibodies that target and suppress specific parts of the immune system. If possible, doctors avoid using radiopaque contrast agents in people who have anaphylactoid reactions to such agents. However, some disorders cannot be diagnosed without contrast agents. In such cases, doctors use contrast agents that are less likely to cause reactions. In addition, drugs that block anaphylactoid reactions, such as prednisone and diphenhydramine , are sometimes given before certain contrast agents are injected.

Anaphylactic reactions typically begin within 15 minutes of exposure to the allergen. Rarely, reactions begin after 1 hour.

Symptoms range from mild to severe, but each person usually has the same symptoms each time. The heart beats quickly. People may feel uneasy and become agitated. Blood pressure may fall, causing fainting, and may become dangerously low shock Shock Shock is a life-threatening condition in which blood flow to the organs is low, decreasing delivery of oxygen and thus causing organ damage and sometimes death.

Blood pressure is usually low Other symptoms include dizziness, itchy and flushed skin, coughing, a runny nose, sneezing, hives Hives Hives are red, itchy, slightly elevated swellings. The swelling is caused by the release of chemicals such as histamine from mast cells in the skin, which cause fluid to leak out of small Angioedema can be a reaction to a drug or other substance trigger , a hereditary disorder People may have nausea, vomiting, abdominal cramps, and diarrhea.

An anaphylactic reaction may progress so rapidly that people collapse, stop breathing, have seizures, and lose consciousness within 1 to 2 minutes. The reaction may be fatal unless emergency treatment is given immediately.

Symptoms may recur 4 to 8 hours after exposure to the allergen or later. Such symptoms are usually milder than they were at first, but they can be more severe or fatal. The diagnosis of anaphylactic reactions is usually obvious based on symptoms such as the following:. Symptoms of shock such as low blood pressure, confusion, cold and sweaty skin, and a weak and rapid pulse. Respiratory symptoms such as difficulty breathing, a gasping sound when breathing in, and wheezing.

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Authored by hundreds of top medical experts. Outflow obstruction can be exacerbated by exercise, vasodilation, and hypovolemia particularly in aortic stenosis and hypertrophic cardiomyopathy , which may precipitate syncope. Arrhythmias Overview of Arrhythmias The normal heart beats in a regular, coordinated way because electrical impulses generated and spread by myocytes with unique electrical properties trigger a sequence of organized myocardial Venous return can be decreased by hemorrhage, increased intrathoracic pressure, increased vagal tone which can also decrease heart rate , and loss of sympathetic tone eg, from drugs, carotid sinus pressure, autonomic dysfunction.

Syncope involving these mechanisms except for hemorrhage is often termed vasovagal or neurocardiogenic and is common and benign. Orthostatic hypotension Orthostatic Hypotension Orthostatic postural hypotension is an excessive fall in blood pressure BP when an upright position is assumed. Cerebrovascular disorders eg, strokes Overview of Stroke Strokes are a heterogeneous group of disorders involving sudden, focal interruption of cerebral blood flow that causes neurologic deficit.

However, basilar artery ischemia, due to transient ischemic attack or migraine, may cause syncope. Rarely, patients with severe cervical arthritis or spondylosis develop vertebrobasilar insufficiency with syncope when the head is moved in certain positions.

The central nervous system CNS requires oxygen and glucose to function. Even with normal cerebral blood flow, a significant deficit of either will cause loss of consciousness.

In practice, hypoglycemia is the primary cause because hypoxia rarely develops in a manner causing abrupt loss of consciousness other than in flying or diving incidents. Loss of consciousness due to hypoglycemia is seldom as abrupt as in syncope or seizures because warning symptoms occur except in patients taking beta-blockers ; however, the onset may be unclear to the examiner unless the event was witnessed.

Causes are usually classified by the mechanism see table Some Causes of Syncope Some Causes of Syncope Syncope is a sudden, brief loss of consciousness with loss of postural tone followed by spontaneous revival. The patient is motionless and limp and usually has cool extremities, a weak pulse Many cases of syncope never have a firm diagnosis but lead to no apparent harm.

A smaller number of cases have a serious cause, usually cardiac. Evaluation should be done as soon as possible after the event. The more remote the syncopal event, the more difficult the diagnosis. Information from witnesses is quite helpful and best obtained as soon as possible.

Important associated symptoms immediately before or after the event include whether there was a sense of impending loss of consciousness, nausea, sweating, blurred or tunnel vision, tingling of lips or fingertips, chest pain, or palpitations.

Length of time recovering should also be ascertained. Witnesses, if any, should be sought and asked to describe events, particularly the presence and duration of any seizure activity. Review of systems should ask about any areas of pain or injury, episodes of dizziness or near-syncope upon arising, and episodes of palpitations or chest pain with exertion. Patients should be asked about symptoms suggesting possible causes, including bloody or tarry stools, heavy menses anemia Etiology of Anemia Anemia is a decrease in the number of red blood cells RBCs , which leads to a decrease in hematocrit and hemoglobin content.

See also Red Blood Cell Production. The RBC mass represents the Past medical history should ask about previous syncopal events, known cardiovascular disease, and known seizure disorders. Drugs used should be identified particularly antihypertensives, diuretics, vasodilators, and antiarrhythmics—see table Some Drug Causes of Syncope Some Drug Causes of Syncope Syncope is a sudden, brief loss of consciousness with loss of postural tone followed by spontaneous revival.

Family history should note presence at a young age of heart disease or sudden death in any family member. Vital signs are essential. Heart rate and blood pressure are measured with the patient supine and after 3minutes of standing.

Pulse is palpated for irregularity. The heart is auscultated for murmurs; if present, any change in the murmur with a Valsalva maneuver, standing, or squatting is noted. Careful evaluation of the jugular venous waves see Figure: Normal jugular vein waves Normal jugular vein waves Complete examination of all systems is essential to detect peripheral and systemic effects of cardiac disorders and evidence of noncardiac disorders that might affect the heart.

Some clinicians carefully apply unilateral carotid sinus pressure during ECG monitoring with the patient supine to detect bradycardia or heart block, suggesting carotid sinus hypersensitivity. Carotid sinus pressure should not be applied if a carotid bruit is present. Abdomen is palpated for tenderness, and a rectal examination is done to check for gross or occult blood.

A full neurologic examination is done to identify any focal abnormalities, which suggest a central nervous system cause eg, seizure disorder. Family history of sudden unexpected death, exertional syncope, or unexplained recurrent syncope or seizures.

Although the cause is often benign, it is important to identify the occasional life-threatening cause eg, tachyarrhythmia, heart block because sudden death is a risk. Clinical findings see table Some Causes of Syncope Some Causes of Syncope Syncope is a sudden, brief loss of consciousness with loss of postural tone followed by spontaneous revival. A few generalizations are useful. Syncope precipitated by unpleasant physical or emotional stimuli eg, pain, fright , usually occurring in the upright position and often preceded by vagally mediated warning symptoms eg, nausea, weakness, yawning, apprehension, blurred vision, diaphoresis , suggests vasovagal syncope.

Syncope that occurs most often when assuming an upright position particularly in elderly patients after prolonged bed rest or in patients taking drugs in certain classes suggests orthostatic syncope. Syncope that occurs after standing for long periods without moving is usually due to venous pooling. Loss of consciousness that is abrupt in onset; is associated with muscular jerking or convulsions that last more than a few seconds, incontinence, drooling, or tongue biting; and is followed by postictal confusion or somnolence suggests a seizure.

Syncope with exertion suggests cardiac outflow obstruction or exercise-induced arrhythmia. Such patients sometimes also have chest pain Chest Pain Chest pain is a very common complaint. Many patients are well aware that it is a warning of potential life-threatening disorders and seek evaluation for minimal symptoms. Other patients, including They are often described as a fluttering, racing, or skipping sensation. They are common; some patients find them unpleasant and alarming Cardiac findings may help identify a cause.