Anaphylaxis

Introduction

• Rapid onset of allergic manifestations in response to an allergen that has sensitised the immune system previously

• Anaphylactoid reactions are clinically indiscernible but do not have an immune-mediated underlying mechanism.

Pathophysiology

• Most common cause is drugs, insect bites and stings, and food

• An IgE mediated release of preformed vasoactive substances including histamine and leukotrienes occurs, resulting in clinical manifestations.

• Thereafter, vasodilation, increased capillary permeabilty, increased mucous production and bronchoconstriction

Clinical • Typically of sudden onset, important features:

– Respiratory• Upper: oropharyngeal oedema, rhinorrhea, layngeal

spasm or oedema• Lower: cough, dyspnoea, bronchospasm and

respiratory distress

– Cardiovascular• Hypotension, tachycardia or syncope

– Cutaneous• Erythema, urticaria, or angio-oedema with pruritus

– Gastrointestinal• Abdominal pain, vomiting or diarrhoea

Adult Guidelines

• Investigations:

- Majority of cases nil investigations required

- Severe cases may require standard pathology studies, CXR and ECG

Treatment

• Basic measures- Triage to appropriate area of ED- Attend to immediate life threat- ABC’s- Remove or cease administration of causative

agent- IV access and fluids

- Monitoring vital signs, ECG and O2 saturation

First line treatment

• O2 to maintain adequate saturation >92%

• Adrenaline- drug of choice in all serious cases - If stable (0.5mg IM of 1:1000) Rpt every 5 minutes as required

according to BP/Pulse/Respiratory function- If unstable initial IV bolus 0.75-1.5mcg/kg, then 10-20mcg IV

increments- If predominantly upper airway manifestations or bronchospasm-

5mg of 1:1000 solution via nebuliser

- IV Fluids

Second line treatment

• Antihistamines- H1 blockers- Promethazine 10-25mg IV, IM or oral

- H2 blockers- Ranitidine 50mg IV, or 300mg orally

• Steroids- Prednisolone 25-50mg orally- Hydrocortisone 100-250mg IV- Dexamethasone 4-8mg IV, IM

• Glucagon- Has a place when patient is on Beta Blockers and relatively resistant to

Adrenaline, or severe refractory anaphylaxis. 1mg IV repeated 5 minutely or by infusion

Disposition• 95% of patients have a uniphasic presentation, and will require

4-8hrs observation prior discharge

• Small amount of people will develop delayed recurrent symptoms, hence the time frame for observation

• If severe cases might require ICU admission

• Most cases can be discharged on antihistmines +/- steroids for 2-3 days with GP follow up

• If cause not known for anaphylaxis, will require further investigations by allergist or immunologist as outpatient

• Need to educate all patients how to manage this in a repeat episode and should be discharged and educated on an epipen

Guidelines

• Australian Prescriber Guidelines– http://www.australianprescriber.com/– Update 2011