Anaphylactic Shock
Anaphylactic shock is a severe and life-threatening allergic reaction that occurs rapidly after exposure to an allergen. It can develop within seconds or minutes and requires immediate medical attention.
Anaphylaxis refers to the characteristic and often life threatening clinical manifestations of the immunoglobulin E (IgE)–mediated immediate hypersensitivity reaction, involving mast cell and basophil degranulation with release of histamine, tryptase, prostaglandins, and leukotrienes, that occurs following exposure to various substances.
Reactions can develop within minutes, but usually less than 1 hour after exposure to a triggering substance. Initial symptoms include flushing, pruritus, and a sense of doom. Clinical manifestations can involve the skin, eyes, respiratory and gastrointestinal tracts, and the cardiovascular and central nervous systems.
Cardiovascular collapse (shock) occurs in approximately 30% of cases and results from
(a) hypovolemia induced by increased vascular permeability and loss of intravascular volume,
(b) hypotension from peripheral vasodilation,
(c) myocardial depression, and
(d) bradycardia.
Up to 50% of patients describe respiratory symptoms, which can progress to respiratory failure from severe upper airway edema, bronchospasm, and cardiogenic and noncardiogenic pulmonary edema. Biphasic reactions occur in up to 20% of patients, characterized by a second round of symptoms 1 to 8 hours after the initial reaction (although up to 72 hours has been reported).
Diagnosis is clinical and involves a broad differential diagnosis including urticaria, status asthmaticus, "red man" syndrome (vancomycin), scromboidosis (histamine-like compound in spoiled fish such as tuna, mackerel, mahi-mahi, and blue fish), carcinoid, pheochromocytoma, mastocytosis, monosodium glutamate ingestion, and panic attacks. Serum levels of tryptase (especially the beta subtype) and histamine, when elevated, support the diagnosis. Tryptase levels are elevated for 1 to 6 hours after the event, but serum histamine levels fall within 30 to 60 minutes. A 24-hour urine N-methyl histamine level compared to a later baseline can be a helpful alternative. Patients should be questioned about exposure to potential triggers, but no substance is identified in up to 60% of cases.
Causes of Anaphylaxis and Anaphylactoid Reactions
Anaphylaxis(IgE mediated)
• Foods (especially nuts, eggs, fish, shellfish, and cow’s milk)
• Antibiotics (especially penicillin)
• Vaccines
• Anesthetics
• Insulin and other hormones
• Antitoxins
• Blood and blood products
• Insect stings and bites (bee, wasp, ant)
• Snake bites
• Latex
• Allergy immunotherapy
Anaphylactoid (direct mastcell degranulation, altered AA metabolism)
• Nonsteroidal anti inflammatory drugs (especially aspirin)
• Opiates
• Sulfites
• Radiocontrast media
• Neuromuscular blocking agents
• Gamma globulin
• Antisera
• Exercise
Clinical Manifestations
• Skin: pruritus, flushing, urticaria, angioedema
• Eyes: pruritus, lacrimation, conjunctival erythema, periorbital edema
• Respiratory: dyspnea, stridor, wheezing, hoarseness, pulmonary edema
• Cardiovascular: hypotension, tachycardia, arrhythmias, cardiac arrest
• Gastrointestinal: nausea, vomiting, diarrhea, abdominal pain
• Neurologic: anxiety, sense of doom, presyncope, syncope, seizures