Anaphylaxis - Adult

Introduction

Anaphylaxis is the exaggerated response of a previously sensitised individual to foreign (antigenic) material. There are three types of reaction.

A. Hypersensitivity, IgE mediated

Prior sensitisation, e.g. with peanuts, bee stings or to Penicillin
Histamine (and other vasoactive mediators e.g. tryptase, leukotrienes) released from mast cells & basophils
Producing respiratory, circulatory, cutaneous and gastrointestinal effects
↑ Vascular permeability and peripheral vasodilation, ↓ venous return and ↓cardiac output
Commonest agents - radiologicals, anaesthetics, antibiotics, dextrans

B. Complement mediated

Hereditary angio-oedema - functional C1 esterase inhibitor

C. Anaphylactoid.

Occurs on first contact with antigen
Due to histamine release, e.g. Aspirin, Morphine, N-Acetyl Cysteine (Parvolex)
No previous sensitisation
IgE is not involved
The treatment is the same.

Diagnosis

A feeling of faintness or impending doom (angst)
Nausea, vomiting, diarrhoea
A rash for example urticaria or erythema

Facial swelling (angio-oedema) involving upper airway
Bronchoconstriction
↓BP = vasodilation & ↑ vascular permeability

Algorithms

Treatment

A & B

The airway should be opened, cleared and maintained
100% O₂ using a reservoir bag

C

After assessing the circulation, commence chest compressions if there is no detectable cardiac output
Connect an ECG monitor
Treat non-perfusing arrhythmias according to standard protocols
Treat bradycardia with atropine
If ↓BP - Give IM Adrenaline (see flow diagram)
If hypotensive, do not sit the patient up
Repeat Adrenaline as necessary (every 5 minutes)
Intravenous fluids to counteract hypovolaemic shock
Rarely (in extremis) titrated intravenous doses of dilute adrenaline may be required

Once cardiac output has been restored, treat as below.

The patient must be admitted to hospital
IV fluid, (10ml/Kg) as a bolus
Bronchodilator by volumatic/nebuliser
Consider IV Aminophylline, 250 mg over 5 mins. (or IV Salbutamol @ 250ug slow loading dose followed by 5-10ug per minute)
Antihistamines (Chlorpheniramine 10 mg IV over 2 min ) for itch
H₂ antagonist ( PO or IV Ranitidine) are unproven
Steroids generally not indicated

Patients who present with simple urticaria, minimal airway involvement and who have a rapid response to Piriton or Histek (Certirizine) ± ranitidine (itch again) can be discharged.

Patients must be admitted if:

There is any degree of bronchospasm
Hypotension
Airway oedema

Even with good initial responses these patients are at risk of a biphasic anaphylactic response where the same problems can arise again.

Follow up

Patients requiring Adrenaline resuscitation warrant admission (CDU) for 12 hours (rebound phenomenon has been reported - but rare).

Prescribe an epinephrine auto-injector on discharge (15-30Kg = 150µg dose, >30kg = 300µg dose).

All patients who require Adrenaline should attend their GP for on-going referral and management.