anaphylaxis
Table of Contents
anaphylaxis
see also
- in Victoria, all anaphylaxis events are mandatory reporting to DHHS - see Anaphylaxis notifications
- in Victoria, allergy events to drugs or blood products should also be entered into the hospital's risk register such as RiskMan
- Western Health:
- ensure allergy is also entered on BOTH EDIS and EMR - see How to enter an unknown allergen in EMR
Clinical features of anaphylaxis
- anaphylaxis is a rapid onset, systemic, type 1 hypersensitivity reaction which is an IgE antibody mediated allergic reaction which results in histamine release and release of other mediators from mast cells which occurs in some 1 in 1000 people but thankfully fatal cases are rare with an annual incidence of only 1 per 5 million population
- it is defined clinically by an acute reaction involving the presence of either1):
- respiratory difficulty, which may be due to laryngeal oedema or bronchospasm (asthma), and/or
- hypotension, which may present as fainting, collapse, or loss of consciousness
- it should be distinguished from benign non-allergic urticaria (the far majority of urticaria with or without angioedema is non-IgE mediated and NOT anaphylaxis) and angioedema (which is at least 100 times more common), and that adrenaline is used only in those patients that truly require it.
- whilst it is critical to avoid delaying adrenaline in a patient with true anaphylaxis, giving a patient a diagnosis of anaphylaxis inappropriately can not only lead to unnecessary prescriptions of adrenaline but may also lead to increased anxiety levels for patients and family.
Differential diagnosis
- benign non-allergic urticaria
- other causes of syncope / near syncope
Brief overview of Mx
early adrenaline as 1st line Rx
- 1:1000 im 0.01ml/kg to maximum 0.5ml (Adult 0.5ml) im into lateral thigh, repeat after 5min if no improvement
- do not give s/c as absorption is unreliable
- do not give iv adrenaline / epinephrine bolus doses unless arrest imminent
- if hypotensive:
- elevate legs, lie patient flat, although may need to have head up at 45 deg if short of breath
- iv fluid boluses of 10-20ml/kg 0.9% saline
- if upper airway obstruction, consider nebulised adrenaline as for croup (below) in addition to im adrenaline
- if inadequate response to repeat im adrenaline dose:
- commence iv adrenaline infusion at 0.05-1.0mcg/kg/min (see adrenaline / epinephrine for infusions)
- if airway obstruction not settling, consider early intubation and rapid sequence induction (RSI) for emergency intubation
- if requires 2 or more adrenaline doses or more than 20ml/kg saline, contact ICU
adjunctive Rx
if wheezing
- nebulised salbutamol as for asthma
corticosteroids
- may be given, especialy if bronchospasm present, although otherwise, no clear benefits demonstrated
- methylprednisolone iv 1mg/kg or hydrocortisone
antihistamines
- may help pruritus
- preferably non-sedating second generation antihistamines (H1)
- avoid promethazine as it is sedating and may cause hypotension
disposition
- all patients with anaphylaxis should be observed for 6-12 hours or overnight as risk of rebound if either:
- more than 1 dose of adrenaline needed
- if iv fluid bolus needed
- if lives too far from hospital to return ASAP
- consider ED Short Stay Observation Unit if suitable
- discharge advice
- consider EpiPen
- a GP cannot prescribe an EpiPEN under PBS as they will need to refer to a paediatrician or immunologist which will delay access, or prescribe a non-PBS more expensive script (~$100)
- an ED doctor CAN prescribe an EpiPEN as follows:
- contact PBS Authority 1800 888 333 to get an authority number (you will need patient's Medicare number)
- authority requirement:
- “Initial sole PBS-subsidised supply for anticipated emergency treatment of acute allergic reactions with anaphylaxis in a patient who has been discharged from hospital or an emergency department after treatment with adrenaline for acute allergic reaction with anaphylaxis.”
- write the PBS Authority script
- AND give the patient a ASCIA anaphylaxis action plan available from here
- AND explain how to use the epiPEN
- consider MedicAlert bracelet
potential precipitants
- new medication or exposure to a chemical
- food:
- immediate reaction soon after eating food
- most type 1 HS reactions to food allergens such as nuts, seafood, pork-cat syndrome
- delayed onset 3-8hrs after eating read meat
- associated with diarrhoea, flushing, wheeze:
- consider carcinoid tumour
- if it was just cutaneous - see urticaria
- if it is just angioedema:
patient information sheets
references and other resources
anaphylaxis.txt · Last modified: 2021/10/26 01:30 by gary1