Anaphylaxis (Allergic Shock)

Anaphylaxis is a severe, life-threatening systemic hypersensitivity reaction that begins abruptly after exposure to an allergen and can affect multiple organ systems. It is typically of immunological origin and develops primarily through immunoglobulin E (IgE)-mediated mechanisms. However, cases arising from non-immunological mechanisms also exist. Accordingly, anaphylaxis is classified into three main categories: allergic (immunological), non-allergic (non-immunological), and idiopathic (unknown cause) anaphylaxis.

Epidemiology

Determining the true prevalence of anaphylaxis is difficult because mild cases are rarely reported and diagnostic criteria have evolved over time. The lifetime prevalence of anaphylaxis in the general population is estimated to range between 0.05% and 2%. It is more common in children and young adults. Although deaths due to anaphylaxis are rare, they typically occur within the first hour after exposure.

Common Causes

The primary causes of anaphylaxis are foods, medications, and insect stings.

• Foods: The most common cause in children. Peanuts, tree nuts, milk, eggs, fish, and shellfish are the most frequently reported triggers.
• Medications: The most common cause in adults, with antibiotics (particularly beta-lactams) and nonsteroidal anti-inflammatory drugs (NSAIDs) being prominent.
• Insect stings: Particularly associated with hymenoptera species such as bees and ants.
• Other causes: Latex, exercise, cold, heat, and other physical factors, immunotherapies, vaccines, certain contrast agents, and rarely idiopathic triggers may also provoke anaphylaxis.

Pathophysiology

The central event in anaphylaxis is the activation of mast cells and basophils, leading to the release of mediators. These cells release preformed substances such as histamine, tryptase, and heparin, as well as newly synthesized compounds including prostaglandin D2, leukotriene C4, and platelet-activating factor. These mediators increase vascular permeability, induce bronchoconstriction, and affect the cardiovascular and gastrointestinal systems.

Risk Factors

Major factors that increase the risk of developing anaphylaxis include being atopic, being in childhood or young adulthood, having coexisting asthma or cardiovascular disease, use of certain medications (e.g., beta-blockers), male sex (in childhood), and higher socioeconomic status. Additionally, individuals with a history of previous anaphylaxis have a high risk of recurrence.

Clinical Features

Symptoms of anaphylaxis typically appear within minutes after exposure to the triggering agent. Cutaneous manifestations (pruritus, urticaria, angioedema) are the most common and occur in the majority of cases. Respiratory symptoms (dyspnea, cough, bronchospasm), circulatory disturbances (hypotension, tachycardia), gastrointestinal symptoms (nausea, diarrhea, abdominal pain), and neurological effects (dizziness, altered consciousness) may also accompany the reaction. Anaphylactic reactions can sometimes follow a biphasic course, with symptoms recurring hours after initial resolution.

Diagnosis

The diagnosis of anaphylaxis is primarily based on clinical findings. The patient’s symptoms are evaluated in conjunction with possible allergen exposure. Any one of the following three clinical scenarios is sufficient for diagnosis:

1. A sudden onset of cutaneous or mucosal symptoms (urticaria, pruritus, swelling of lips or tongue) accompanied by respiratory distress or circulatory compromise (e.g., hypotension).
2. Involvement of two or more organ systems following exposure to a likely allergen (e.g., skin symptoms along with respiratory, circulatory, or gastrointestinal symptoms).
3. A marked drop in blood pressure after exposure to a known allergen.

Laboratory tests are generally used to support the diagnosis. Elevated levels of histamine and tryptase in the blood during the acute phase may indicate mast cell activation. Tryptase levels are particularly helpful in diagnosing drug- and venom-induced anaphylaxis. However, normal test results do not exclude anaphylaxis. Differential diagnosis should consider vasovagal syncope, panic attack, asthma attack, carcinoid syndrome, food poisoning, and other non-allergic conditions.

Monitoring and Education

Patients who have experienced anaphylaxis should be observed in a healthcare facility for a specified period after emergency treatment. The duration of observation varies depending on the severity of the reaction and individual risk factors but generally lasts at least 4–6 hours and may extend up to 24 hours in some cases. The risk of biphasic reactions is particularly elevated in patients who received delayed epinephrine or were exposed to allergens via the gastrointestinal route.

After discharge, patients and their families must be educated. Education should include:

• Strategies to avoid potential triggers,
• Recognition of anaphylaxis symptoms,
• Location and proper use of epinephrine auto-injectors,
• Actions to take during an emergency (e.g., positioning, calling for help),
• Development and carrying of a written “anaphylaxis emergency action plan.”

Individuals who must carry an epinephrine auto-injector at all times should also be informed about the device’s expiration date and storage conditions.

Social and Clinical Preventive Measures

Preventive measures for anaphylaxis must be implemented not only at the individual level but also within the healthcare system. Healthcare facilities must ensure continuous availability of emergency equipment and medications for anaphylaxis, and healthcare workers must be adequately trained in its diagnosis and management. Including allergy alerts in hospital records, wristbands, or identification cards for at-risk individuals facilitates prompt and accurate intervention.

Today’s widely available epinephrine auto-injectors have been formulated with different dose options to suit children and adults. However, the lack of precise dosing for every age and weight group remains a challenge, especially in young children. Therefore, in special circumstances, traditional syringe-based administration may be preferred.

Anaphylaxis is a severe emergency characterized by rapid onset, potential lethality, and multi-system involvement. It can be effectively managed with early diagnosis and appropriate monitoring. Proper education of diagnosed individuals, consistent carriage of auto-injectors, and regular follow-up play a fundamental role in preventing recurrent episodes and reducing complications.

Warning: The content provided in this article is intended solely for general encyclopedic informational purposes. The information presented here should not be used for diagnosis, treatment, or medical advice. Always consult a physician or qualified healthcare professional before making any decisions regarding health matters. The author and KÜRE Encyclopedia assume no responsibility for any consequences arising from the use of this information for diagnostic or therapeutic purposes.