Anaphylaxis and the Immune System

Anaphylaxis

• Anaphylaxis is an exaggerated hypersensitivity reaction to a previously encountered antigen.
• It involves a series of potentially life-threatening events affecting multiple body systems.
• Anaphylactic shock is a serious, rapid allergic reaction that can be fatal.
• Symptoms include shortness of breath, fainting, itching, throat swelling, and sudden drop in blood pressure.

Learning Objectives

• Students will be able to list symptoms of anaphylactic shock.
• Students will be able to discuss the role of the immune system in fighting antigens.
• Students will be able to define an allergic reaction.
• Students will describe the body's response to foreign substances.
• Students will identify the most common cause of death from anaphylaxis.
• Students will discuss medications used to treat anaphylaxis.
• Students will be able to demonstrate the proper procedure for using an epinephrine autoinjector.

Immune System

• The immune system mitigates harmful substances entering the body, ensuring essential bodily functions.
• It identifies and targets antigens (foreign molecules that trigger specific responses).

Immune Response

• The immune system forms proteins called antibodies (immunoglobulins) that target specific antigens.
• Antibodies use various mechanisms to destroy or remove the antigens from the body.
• In autoimmune disorders, the system attacks healthy body cells and tissues, causing harmful effects.

Allergic Response

• Hypersensitivity to a particular antigen is out of proportion to its actual hazard to the body.
• The allergic response, rather than the antigen, is the real threat.
• Common causes of allergic reactions include food, medications, insect stings, and airborne allergens like animal fur and dust mites.
• Allergens are substances or antigens that cause exaggerated allergic reactions.

Anaphylactic Shock

• Anaphylactic shock is often triggered by drugs (e.g., penicillin) or insect bites/stings.
• Symptoms include skin rashes (hives), itching, redness, swelling (edema), shortness of breath, fainting, swelling of the throat, and a sudden drop in blood pressure.
• The patient may feel warm, flushed, with swollen lips and eyelids, and watery eyes.

Anaphylaxis Pathophysiology

• In response to allergens, cells in the body release chemical mediators, primarily histamine.
• Histamine release causes vasodilation (drop in blood pressure), decreased peripheral tissue perfusion and oxygen delivery, increased capillary permeability (edema of the airway), and spasms of smooth muscles (diarrhea, vomiting, laryngospasm).
• The severity of the reaction, determines whether it's an allergic reaction or anaphylaxis.
• Symptoms typically appear within minutes to an hour after exposure, with faster onset indicating a more severe threat to life.
• Laryngeal edema (swelling of the vocal cords) can cause varying degrees of airway obstruction, along with tightness in the chest, shortness of breath, and lightheadedness.
• Patient history generally confirms the diagnosis of allergic response and anaphylaxis.

Anaphylaxis Management

• Most deaths from allergies result from airway obstruction.
• Prompt and thorough assessment of the airway and breathing is critical.
• Patients with airway or breathing problems should receive immediate assistance while their history is taken.

Epinephrine

• Epinephrine (adrenaline) is the first-line treatment for anaphylaxis.
• It's administered intramuscularly (IM)
• It increases the rate and force of heart contractions, increasing cardiac output.
• It relaxes bronchial smooth muscle.
• It causes peripheral vasoconstriction, raising arterial blood pressure.
• Epinephrine should be administered as quickly as possible.

Epinephrine Administration

• Proper IM administration is crucial.
• Inject into the outer middle third of the thigh (vastus lateralis).
• Maintain circulatory integrity by administering fluids such as saline or Ringer's lactate to maintain sufficient volume in the vascular space to promote adequate perfusion.

Oxygen

• Establish an airway.
• Administer high levels of supplementary oxygen, preferably using a non-rebreather mask at 15 liters per minute.

Second-Line Medications

• Second-line medications (e.g., antihistamines, corticosteroids, bronchodilators) help with broader management but do not replace epinephrine.
• Salbutamol (albuterol) stimulates beta2 receptors, causing bronchodilation.
• Hydrocortisone has anti-inflammatory properties, helping prevent later complications like laryngedema and urticaria.
• Steroids aren't helpful in acute anaphylaxis but can help avoid later responses.
• Antihistamines with anticholinergic properties (like chlorphenamine) help block histamine effects.
• Nebulizer treatments with bronchodilators (like salbutamol) may help with ongoing respiratory distress.

Resuscitation Council UK Guidelines

• Updated guidelines in May of 2021 emphasize the importance of recognizing anaphylaxis and quickly correcting airway, breathing, and circulation problems.
• Early administration of adrenaline (epinephrine) with repeat doses every 5 minutes is crucial.
• IV fluids are used for refractory anaphylaxis or developing shock.
• Corticosteroids are no longer a first-line medication, and proper local guidelines should be followed.

Research

• Research should focus on the specific drugs and dosages for allergic reactions and anaphylaxis, following JRCALC guidelines.

Medications to review

• Epinephrine autoinjector
• Salbutamol
• Chlorphenamine
• Hydrocortisone

This quiz covers the critical aspects of anaphylaxis, including its symptoms, causes, and potential life-threatening effects on the body. Students will learn about the immune system's role in allergic reactions and how to respond effectively. Key topics include treatment options and the use of epinephrine autoinjectors.