Anaphylaxis

Anaphylaxis is a severe and rapid allergic systemic reaction to an allergenic trigger substance (atopic or anaphylactic hypersensitivity). Minute amounts of trigger substances may cause a life-threatening anaphylactic reaction. Anaphylaxis may occur after ingestion, inhalation, skin contact or injection of a trigger substance. The most severe type of anaphylaxis - anaphylactic shock - will usually result in death if untreated.

Immediate action

Anaphylactic shock is a life-threatening medical emergency because of rapid constriction of the airway, often within minutes of onset. Call for help immediately. First aid for anaphylactic shock consists of obtaining advanced medical care at once; rescue breathing (a skill which is part of CPR) is likely to be ineffective but should be attempted if the victim stops breathing. Look to see if a device such as an Epi-pen is available for administration of epinephrine by a layperson. You should however be aware that if you administer an Epi-pen where the patient has already done so prior to going unconcious, this can have severe effects on the heart. Pulse rates in double-administration cases have been known to pass extreme ventricular tachycardia levels - up to 240 BPM in some cases.

Symptoms

Symptoms can include respiratory distress, hypotension (low blood pressure), fainting, unconsciousness, urticaria (hives), angioedema (swelling) and itching. The symptoms are related to the action of immunoglobulin E (IgE) which acts to release histamine and other mediator substances from mast cells. Histamine induces, beside other effects, vasodilation and bronchospasm (constriction of the airways).

Causes

Common causative agents in humans include food ingredients (nuts, peanuts, fruits), drugs (e.g. penicillin, contrast media, NSAIDs, such as Ibuprofen or Sodium Diclofenac), latex, bee or wasp stings, and exercise (see exercise-induced anaphylaxis). Transfusion of incompatible blood products may cause an equivalent syndrome.

Treatment

Paramedic treatment in the field may include injection with epinephrine (unless the patient has self-administered an Epi-pen), administration of oxygen therapy and, if necessary, intubation during transport to advanced medical care.

The clinical teatment of anaphylaxis by a doctor and in the hospital setting aims to treat the cellular hypersensitivity reaction as well as at the symptoms. Antihistamine drugs (which inhibit the effects of histamine at histamine receptors) are given but usually not sufficient in anaphylaxis, and high doses of intravenous corticosteroids are often required. Hypotension is treated with intravenous fluids and sometimes vasoconstrictor drugs. For bronchospasm, brochodilator drugs are used. In severe cases, immediate treatment with epinephrine may be lifesaving. Supportive care with mechanical ventilation may be required.

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