Anaphylactic Shock Study Notes

Definition: Anaphylaxis is a severe systemic allergic reaction characterized by respiratory difficulties and/or hypotension. Other clinical features may be present as well.
Position in Allergy Spectrum: It represents the extreme end of the allergic spectrum, suggesting that it is the most severe form of allergic response.
Clinical Presentation: Typically, more than one part of the body is affected, often within minutes of exposure to the allergen, although symptoms can occasionally manifest after several hours.
Mechanism of Reaction: Hypersensitivity reactions in anaphylaxis are primarily mediated by antibodies known as immunoglobulin E (IgE).

Immune Response Initiation: When an antigen (an allergenic substance) is first encountered, the immune system produces IgE antibodies.
Sensitization Explained: These IgE antibodies attach to the surfaces of mast cells and basophils, leading to a state referred to as sensitization (which denotes the first exposure to the antigen).
Analogy: Mast cells and basophils with IgE are likened to “bombs waiting to explode,” releasing their contents into the circulatory system upon re-exposure to the allergen.
Mechanism of Degranulation: Upon subsequent exposure, the allergen binds to the specific IgE on mast cells and basophils, inducing degranulation and leading to the release of histamine and other chemical mediators, triggering the allergic reaction.

Location: Mast cells and basophils are primarily located in the lungs, small intestine, skin, and connective tissue.
Effects of Degranulation:
- Histamine Release: Histamine and heparin are released during degranulation, resulting in:
- Smooth muscle contraction
- Increased vascular permeability
- Increased gastric acid secretion
- Systemic vasodilation
- Cardiovascular stimulation

Components Involved:
- Mast Cells: Store granules of histamine.
- Basophils: Contain inflammatory mediators.
- Allergens: Examples include pollen, animal hair, drugs (like antibiotics), insect stings.
Generalized Symptoms of Anaphylaxis:
- Cardiovascular collapse
- Oedema (swelling)
- Bronchospasm
- Vomiting

Description: Anaphylactoid reactions occur when certain substances directly cause mast cell degranulation, releasing chemical mediators.
Characteristics: This reaction is not IgE mediated and does not require prior sensitization to the substance.
Common Triggers: Substances that could cause anaphylactoid reactions include opiates, opaque contrast media, and physical factors (e.g., cold or exercise).

Urticaria: Indicative symptoms include pruritus, flushing, and raised areas on skin.
Angioedema: Prominent swelling, especially around the face and lips.
Conjunctivitis (inflammation of the outer membrane of the eyeball).

Symptoms stemming from allergic substances entering circulation include:
- Hypotension (low blood pressure)
- Tachycardia (increased heart rate)
- Other signs may include pallor and faintness.

Degranulation leads to:
- Fluid loss from blood vessels into the gut lumen resulting in symptoms such as:
- Abdominal cramps
- Vomiting
- Diarrhoea

Immediate identification and treatment are crucial for anaphylactic reactions.
Action Protocol:
- Assessment: Conduct an initial assessment including Airway, Breathing, Circulation, Disability, Exposure (ABCDE).
- Adrenaline Administration:
- Dosage for Adults: 0.5 ml of 1:1000 IM (500 micrograms, mcg), may be repeated after 5 minutes if no improvement.
- For Life-Threatening Shock: IV adrenaline at a dilution of 1:10,000 should be administered with caution.
Mechanism of Action:
- Adrenaline acts on both alpha and beta receptors, reversing peripheral vasodilation and reducing oedema, while also dilating bronchial smooth muscles and increasing cardiac contractility.
Side Effects: Possible anxiety, tremor, tachycardia, arrhythmias, headache, cold extremities, hypertension, risk of cerebral hemorrhage, and pulmonary edema.
Cautions: Though there are no absolute contraindications, caution is advised in patients with pre-existing heart disease.

Dosage: 0.3 ml of 1:1000 solution (300 mcg) for emergency treatment.
Administration Tips: Remove the safety cap, place the pointed end on the outer thigh, and push until a click is heard. Hold for 10 seconds before removing.

Dosage: 10-20 mg IM or slow IV injection for patients >12 years old; 4mg tablets every 4-6 hours, max 24 mg daily.
Mechanism: H1 antihistamine blocking to inhibit histamine effects.
Side Effects: Drowsiness, urinary retention, dry mouth, blurred vision, with risks associated with hypotension.

Dosage: 100 mg IM or slow IV for patients over 12 years.
Mechanism: Inhibits inflammatory pathways but may take 4-6 hours for onset of action.
Side Effects: Gastrointestinal issues, cardiovascular effects; minimized with the lowest effective dose.

Note: Approximately 50% of intravascular volume may be lost within 10 minutes of onset of anaphylaxis.
Actions: If hypotension is unresponsive to medication, crystalloid fluid should be infused for restoring volume.

Immediate treatment protocol includes identifying a comprehensive action plan for different settings (hospital vs. community).
Continuous monitoring of the patient, including ECG and pulse oximetry is essential.

Statistics indicate that about 40% of patients experience another episode of anaphylaxis within 24 hours.
Continuous support, monitoring, and referral to allergy specialists are crucial for prevention.

What is an antigen?
- A mast cell
- An allergic substance
- A basophil
- A chemical mediator
What is the dosage of Adrenaline to treat anaphylaxis?
- 500mcg of 1:1000 IM
- 500mcg of 1:1000 IM
- 300mcg of 1:1000 IM
- 500 mcg of 1:1000 IV
What does the action of histamine lead to?
- Smooth muscle contraction and vascular permeability
- Enhanced gastric secretion
- Disruption of the nervous system
- All of the above

Feel free to ask any additional questions if needed.