Anaphylaxis: Symptoms, Causes, and Treatment

• Anaphylaxis is a serious allergic reaction that is rapid in onset and can be fatal.

Learning Objectives

• Differentiate anaphylaxis from common allergies
• Discuss the pathophysiology, diagnosis and treatment of anaphylaxis, including applied pathophysiology.

Allergy vs. Anaphylaxis

• Allergies involve mild, localized skin symptoms like swelling of the lips/face, or generalized skin reactions.
• Anaphylaxis involves airway, breathing, or circulation problems, with or without skin symptoms.
• Anaphylaxis is a "missing protection" response
• Allergies represent a "strange reaction" in the body.
• An absence of airway, breathing, or circulation problems likely indicate that it is not anaphylaxis.

Grades of Anaphylaxis

• Grade I: Local reaction with symptoms like redness, swelling, and pruritus.
• Grade II: Mild to moderate systemic reaction with symptoms like urticaria, angioedema, flushing, abdominal pain, vomiting, and diarrhea.
• Grade III: Severe systemic reaction, which is anaphylaxis as the reaction involves respiratory and/or cardiovascular issues.
• Grade III A involves either cough, wheezing, or stridor.
• Grade III B includes objective dyspnea and accessory muscle use.
• Grade III C includes either respiratory or cardiovascular arrest.

Allergies

• Allergies are the body's response to normally harmless substances.
• Common allergens include pollen, foods, insects and pets.
• Allergies affect more than 1 in 4 people in the UK.
• Allergy symptoms include sneezing, wheezing, coughing, runny nose, hives, vomiting, and diarrhea.

Anaphylaxis defined

• Anaphylaxis is a severe, life-threatening, generalized or systemic hypersensitivity reaction.
• Immediate treatment and is recognized as a medical emergency.
• Symptoms include oropharyngeal swelling, wheezing, difficulty breathing, and possible cardiovascular collapse.

Statistics of Anaphylaxis in the UK

• 1 in 1,333 people in the UK have experienced anaphylaxis at some point.
• Approximately 20 anaphylaxis-related deaths are reported each year in the UK.
• Medical treatment causes about half of these anaphylaxis deaths.
• 1 in 25 anaphylaxis cases results in a biphasic reaction.
• Anaphylaxis occurs during general anaesthesia in 1 in 10,000 - 20,000 anaesthetics.

Pathophysiology

• Allergic responses often involve high levels of immunoglobulin E (IgE) against a specific allergen.
• B-lymphocytes mature into plasma cells, producing IgE antibodies against the allergen.
• Mast cells, found throughout the body, have IgE receptors.
• They become sensitized when IgE circulates in the blood and binds to them.
• Subsequent exposure to the same allergen causes a quick reaction with the IgE antibodies coating the mast cells.
• Mast cells degranulate, releasing histamine and other inflammatory mediators into local tissues.
• Histamine induces widespread vasodilation.
• This results in a rapid drop in blood pressure leading to weakness, collapse, and loss of consciousness.
• Histamine also affects the smooth-muscle layers of the bronchial tree, causing bronchoconstriction.
• This further leads to increased mucus production from goblet cells
• Platelet-activating factor (PAF) is released during anaphylaxis, increasing vascular permeability synergistically with histamine.
• Histamine quickly initiates local vasodilation.

Effects in Context

• Formula to understand vasodilation is: SV x HR=CO & CO X SVR=BP
• Capillary Permeability can result in loss of volume.
• Loss of Blood Volume = Loss of 02 carrying capacity
• Bronchoconstriction results in respiratory distress due to ventilation/perfusion mismatch.

Airway and Breathing during Anaphylaxis

• Histamine affects the airway by binding to receptors in the bronchial tree, causing bronchoconstriction, stimulating mucus production.
• Histamine and PAF increase vascular permeability in the airways, causing swelling/oedema.
• Resistance and swelling in the airways causes breathing distress.
• Exudate forms in soft tissues such as lips, mouth, and tongue with ingested allergens.
• Mediators of inflammation exacerbate bronchial swelling, possibly leading to emergency intubation.

Circulation during Anaphylaxis

• Endothelial permeability is increased, leading to fluid extravasation and edema formation, and reduction in blood pressure.
• Peripheral vasodilation further lowers blood pressure by reducing venous return and causes anaphylactic shock.
• Cardiac output decreases due to loss of volume, possibly leading to myocardial damage or ventricular dysfunction.
• Circulating blood volume can decrease by 35% within 10 minutes due to fluid transfer to extravascular spaces.
• Vasodilation increases blood flow demand, but is insufficient due to excessive permeability.

Disability & Exposure during Anaphylaxis

• Mast cells and basophils in the circulation penetrate tissues, causing rashes.

Anaphylaxis Symptoms

• Anxiety and confusion
• Difficulty swallowing or hoarse voice
• Bronchial or facial swelling
• Wheezing
• Heart palpitations
• Fluid in the lungs
• Drop in blood pressure
• Skin discoloration
• Hives, abdominal pain
• Stomach problems

Anaphylaxis Algorithim

• Assess: A=Airway, B=Breathing, C=Cirulation, D=Disability, E=Exposure
• Diagnosis by:
  • Sudden onset of Airway, Breathing and/or Circulation issues
  • Skin changes (e.g. itchy rash)
• Call for help.
• Administer an Intramuscular (IM) injection of adrenaline.
  • Middle, anteriolateral part of the thigh should be targetted
  • Remove triggger and lay patient flat
• If there is no improvement of Breathing or Circulation problems, proceed with the REFRECTORY ANAPHYLAXIS ALGORITHM

Intramuscular (IM) Adrenaline Doses

• Adults and Children older than 12yr - 500mcg (0.5mL)
• Child (6-12yr) - 300mcg (0.3mL)
• Child (6mo-6yr) - 150mcg (0.15mL)
• Child (<6mo) - 100-150 (0.1mL-0.15mL)

High Dose vs Low Dose Adrenaline

• High dose has mainly ALPHA affect
• LOW dose has mainly BETA affects

Refractory Anaphylaxis

• "Refractory" anaphylaxis requires continuous treatment because of persistent cardiovascular/respiratory symptoms.
• This occurs despite administering two doses of IM adrenaline.
• Establish IV/IO access
• Administer fluids, and start adrenaline infusion alongside ABC treatment.

Perioperative Anaphylaxis

• Antibiotics at 48% and neuromuscular blockades at 25% are the most common triggers.
• Most common clinical signs include tachycardia, hypotension or bronchospasm and cutaneous features.

Explore the key differences between allergy and anaphylaxis, common symptoms, and the estimated occurrence of anaphylaxis during general anesthesia. The quiz also covers the effects on cardiac output, recommended treatments, and potential skin findings that may indicate anaphylaxis.