Emergency Medicine: Anaphylaxis Pathophysiology, differentials, - PowerPoint PPT Presentation

Emergency Medicine: Anaphylaxis Pathophysiology, differentials, investigations and management. Cases Quiz Dr Shuaib Siddiqui, MB Bchir MRCP, FY3 Doctor Emergency series Content reviewed on the 14/05/2020.

Case 1 History A 13-year-old boy attends the emergency department by ambulance, accompanied by his worried parents. His parents reveal he suddenly became wheezy whilst at a birthday party. He was unable to speak due to a swollen tongue. On examination, he is blue in the face with audible stridor. There is an urticarial rash on his trunk Observations HR 140, BP 88/45 mmHg, RR 28, SpO2 87%, Temp 37.2 2

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Case 1 History A 13-year-old boy attends the emergency department by ambulance, accompanied by his worried parents. His parents reveal he suddenly became wheezy whilst at a birthday party. He was unable to speak due to a swollen tongue. On examination, he is blue in the face with audible stridor. There is an urticarial rash on his trunk Observations HR 140, BP 88/45 mmHg, RR 28, SpO2 87%, Temp 37.2 5

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Pathophysiology Definition: rapid onset , life-threatening changes to airway, breathing and circulation due to a hypersensitivity reaction. (1) 9

Degranulation Pathophysiology Pathophysiology 1. 2. 3. Life-threatening Bronchospasm Hypotension laryngeal & increased oedema mucous membrane secretion Stridor Wheeze Anaphylactic (+ respiratory shock (+ respiratory distress) distress) 10

Differential diagnoses Pathophysiology Allergic reaction Anaphylaxis Anaphylactoid • IgE mediated IgE mediated Not antibody mediated • Non IgE mediated Requires sensitisation Requires sensitisation Can occur on first exposure Systemically well ABC compromise ABC compromise 11

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Pathophysiology Definition: rapid onset , life-threatening changes to airway, breathing and circulation Pathophysiology due to a hypersensitivity reaction. Epidemiology • 0.3% of people experience anaphylaxis in their lifetime (NICE) • Mortality < 1% Risk factors • History of atopy: asthma, eczema, allergy • Food is a common allergen in children • Drugs are a common allergen in adults • Previous anaphylactic reaction • (Hygiene hypothesis) 13

Clinical features Pathophysiology Symptoms Signs Exposure to allergen Hypotensive and tachycardic Angioedema : Tachypnoeic • Swelling of the face, tongue, larynx, genitalia, hands and feet Pruritis and rash Stridor Dizziness Urticarial rash Syncope

Clinical features Pathophysiology (2)

Clinical features Pathophysiology (3)

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A-E assessment Airways • Assess airway patency by asking patient to speak • Listen for evidence of obstruction e.g. stridor • Start with airway manoeuvres, such as a head tilt before airway adjuncts (4) (5) 18

A-E assessment Breathing – Rule of 5 1. Observations: Respiratory rate, oxygen saturations Peripheral cyanosis 2. Peripheral exam: Tracheal deviation, percussion, auscultation 3. Central exam: ABG, CXR 4. Urgent investigations: 5. Management: Oxygen therapy, nebulised therapy 19

A-E assessment Circulation – Rule of 5 1. Observations: Heart rate, blood pressure, fluid status 2. Peripheral exam: CRT, pulse 3. Central exam: JVP, central CRT, auscultate 4. Urgent investigations: ECG, cannula, bloods 5. Management: Fluids, vasopressors 20

A-E assessment Disability 1. GCS 2. Pupils 3. Glucose Exposure 1. Top to toe examination of the patient 21

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Adrenaline Airway • Alpha agonist à vasoconstriction leads to reduction in laryngeal oedema Breathing • Beta 2 agonist à bronchodilation Circulation • Beta 1 agonist à increased cardiac contractility • Alpha agonist à vasoconstriction Termination • Beta 2 agonist à inhibition of mast cells • Histamine antagonist 24

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Anaphylaxis protocol Airways • The patient has stridor Dose: 0.5ml 1:1000 (0.5mg) • Attempt airway manoeuvres • 1:1000 = 1g in 1000mls = 1000mg in 1000mls = 1mg in 1ml • Give adrenaline Breathing 1. Observations: RR 28, 87% O 2 2. Peripheral exam: cyanosed 3. Central exam: cyanosed, wheeze 4. Urgent investigations: CXR 5. Management: High flow oxygen 26

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Anaphylaxis protocol Circulation 1. Observations: 88/45mmHg, HR140 2. Peripheral exam: weak pulse 3. Central exam: central CRT 4 seconds 4. Urgent investigations: cannula and bloods 5. Management: IV access and bloods Disability – patient may be unconscious Exposure – may find a rash 28

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Investigations Primary investigations: Pathophysiology • Mast cell tryptase 1) Immediately after treatment has commenced 2) 1-2 hours post-reaction 3) 24 hours post-reaction Outpatient investigations to consider: • Skin prick test • Skin patch test • Radioallergosorbent test (RAST) • Challenge test: contraindicated in anaphylaxis 32

Skin prick test Skin patch test Pathophysiology • Diluted food/pollen allergy is • Multiple allergens taped to the back • Assess for contact dermatitis after placed on skin and pierced with 48h needle • A wheal develops after 15 mins (6) (7) 33

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Complications Biphasic reaction : Pathophysiology • Symptoms may return, usually within 6 hours of the initial episode, without re-exposure to allergen Cardiorespiratory arrest : • Food: 30 mins • Insect sting: 15 mins • Medication: 5 mins Recurrence : • A previous episode of anaphylaxis correlates with an increased risk of a future anaphylactic reaction 35

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References 1) Paweł Kuźniar (Jojo_1, Jojo) [CC BY-SA (http://creativecommons.org/licenses/by-sa/3.0/)] 2) James Heilman, MD / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0) 3) James Heilman, MD / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0) 4) Another-anon-artist-234 / CC0 5) ICUnurses / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0) 6) Wolfgang Ihloff / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0) 7) Jan Polák / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0) All other imag ages ar are from Shutterstock (bas asic license) or mad ade by Bi BiteM eMed edicine an and not ap appropriate for redistribution. 38