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Anaphylactic shock is a life threatening condition caused by a runaway histamine response to an allergic reaction.

In a normal human body, histamines are released when the body detects that foreign matter of any type has penetrated the skin, mucous membranes, or digestive system. The histamines signal the body to send blood to the affected area, which causes swelling from edema and inflammation. In the case of a typical reaction, such as a mosquito bite, the swelling and inflammation are very localized and merely act to restrict blood flow and access to the bloodstream at the site. A histamine reaction is also typical when the body is invaded by a parasite.

However, for reasons that are not totally understood, in some individuals the histamine response is triggered by substances that are not inherently harmful to the human body or a normal histamine response is atypically aggressive, causing the normal symptoms associated with a histamine response to be somewhat more severe. This condition is known as an allergy. In most allergy sufferers, this histamine response is annoying, but not life threatening. For example, the sufferer may have an excessively runny nose, hives or a rash.

However, in some individuals, the histamine response continues unabated. Body tissues swell up, blood vessels throughout the body become constricted, and the bronchial tubes in the lungs become inflamed, constricted and full of mucous. As a result, the individual's breathing starts to become labored and if left untreated the sufferer can die from suffocation.

Luckily, an injection of adrenaline or a synthetic equivalent like epinephrine will immediately reverse the histamine response and allow fluid to drain from the body's tissues. There are several similar products, the best known of which is the EpiPen(TM), which will automatically inject an appropriate dose of epinephrine when jammed into the thigh muscle and can be carried by persons who suffer life threatening reactions. However, although the sufferer will recover quickly, hospital care is still required to ensure there are no other complications from the attack.

The amount of allergen needed to set off an attack is often minuscule. A single bee sting or traces of peanuts in otherwise peanut free foods are enough to bring on an attack. The bursting of a parasitic cyst inside a body will also bring on anaphylactic shock even in an otherwise healthy patient.

A panic attack is often mistaken for anaphylactic shock as it also presents as a seeming inability to breathe. However, injecting adrenaline for a panic attack will naturally make the symptoms worse. The two conditions can usually be distinguished by the fact that respiration and heartbeat become rapid in anaphylactic shock, while they remain close to normal in a panic attack despite the perception that the patient is having trouble breathing.

Anaphylaxis at NIH

Anaphylaxis at Wikipedia

Anaphylaxis at Mayo Clinic