Anaphylaxis Flashcards
Define anaphylaxis
A severe, life-threatening, generalised or systemic hypersensitivity reaction
- IgE-mediated Type 1 hypersensitivity reaction
- Degranulation of mast cells releases vasoactive mediators including histamine, prostaglandins, and leukotrienes
- Histamine mediates systemic vasodilation, cardiac contractility, and vascular permeability
Characterised by rapidly developing life-threatening airway and/or breathing and/or circulation problems usually associated with skin and mucosal changes
Can be biphasic:
- Once initial reaction has been treated - it returns without re-exposure to the allergen
- Can be greater/less/similar severity
- Possibly more common if hypotension is a presenting feature
- Less common overall - up to c.20% of reactions
What are some triggers for anaphylaxis?
Antibiotics - penicillin, cephalosporin etc
Other drugs - NSAIDs, ACE-i, contrast media
Blood products
Anaesthetic drugs - suxamethonium
Food - nuts, milk, fish, crustaceans, egg etc
Latex
Stings from insects
How may anaphylaxis present?
Sudden onset and rapid progression of symptoms - over several minutes
Life-threatening problems with one or more of the following:
Airway:
- Airway swelling, e.g. throat and tongue swelling (pharyngeal/laryngeal oedema)
- Difficulty in breathing and swallowing and feels that the throat is closing up
- Hoarse voice
- Stridor
Breathing:
- Shortness of breath
- Wheeze
- Hypoxia - leading to confusion
- Cyanosis (usually a late sign)
- Respiratory arrest
Circulation:
- Pallor
- Tachycardia
- Hypotension
- Dizziness
- Collapse
- Myocardial ischemia, possible cardiac arrest
Skin and/or mucosal changes:
- Often the first feature, can be of variable severity/appearance
- Flushing, urticaria, angioedema - itchy
How do you manage anaphylaxis?
Early recognition - call for help - ABCDE assessment - change patient position depending on symptoms:
- Remove exposure to allergen if known and possible
- Breathing collapse - may sit up as easier to breathe, if shocked, may lie down and raise legs to increase venous return
- Secure airway - high flow O2
Adrenaline IM if indicated and available (500mcg adults in 0.5mL 1 in 1000 solution, 0.15-0.3mg paeds)
- Repeat after 5 mins if no improvement
- IV only with specialists + cardiac monitoring
IV access:
- IV fluid challenge e.g. with 1L Hartmann’s or 0.9% saline; may need IO
- FBC, U+E, Mast cell-tryptase (just after adrenaline given, at 1-2hrs post and 6-24hrs post - for immunology follow up and epipen prescription)
After initial resus:
- Chlorphenamine - antihistamine = 10mg slow IV
- Hydrocortisone - steroid = 200mg slow IV (may shorten protracted reactions, takes 2+hrs to exert effects and reduce risk of biphasic/prolonged reactions)
May also need:
Bronchodilators e.g. salbutamol NEB OR adrenaline 1:1000 5ml (5mg) NEB - both for bronchospasm
Once recovered - needs monitoring for several hours to watch for biphasic presentation (tell patient this is possible)
How does discharge work following an anaphylactic reaction?
Observations for 6-12hrs - especially if:
- Unknown trigger
- Severe asthmatic component
- Those presenting in the eve/night
- Those who find access to care difficult
Given advice about symptom recurrence and what to do
- Given an alert band to identify their allergy
Considered for antihistamines and steroids PO for 3/7
May be prescribed an adrenaline autoinjector/epipen = to manage any acute reactions alone before hospital
What are type 1 allergic reactions?
Occur within minutes-2hrs of exposure, but not always to the first dose (as might need to be sensitised first)
- Can be very rapid with parentral administration, with cardiac arrest occurring within 5 minutes in fatal cases
Typical Sx:
- Itching
- Urticaria
- Hypotension
- Angioedema
- Wheeze
What types of rashes/skin changes are possible with drug reaction?
Urticaria + angioedema = typical allergic responses
- Urticaria can also arise due to other infections
- Angioedema can arise due to ACE-i’s
- Care must be taken when establishing a timeline
Morbilliform rash:
- Resembles urticaria but patches enlarge and become confluent over several days whereas in urticaria patches subside and reappear elsewhere
Erythema multiforme:
- Secondary to infection, or drugs e.g. penicillins, phenytoin, statins
- May progress rapidly to SJS and TEN
Fixed drug eruptions:
- Erythematous plaques that appear in the same place each time a drug is taken e.g. paracetamol, tetracyclines, NSAIDs
What is the relationship between penicillins and other antibiotics?
Cephalosporins:
- Individuals reacting with anaphylaxis/urticaria/rash immediately following penicillin exposure are at risk of reacting to cephalosporins and other beta-lactams - as sensitivity related to same basic structure
- Cross reactivity = higher with: 1st gen e.g. cefalexin** + 2nd gen e.g. cefuroxime
- and less with 3rd+ e.g. ceftriaxone, cefotaxime, cefepime
Carbapenems:
- Meropenem, imipenem, etrapenem, doripenem
- c. 1% of pen-allergic patients show evidence of allergy to these
(Monobactams e.g. aztreonam = safe in pen-allergic despite their beta-lactam ring)
What are some risk factors for developing allergic reactions to drugs?>
Atopic individuals:
- More severe reactions
- More likely to react to radiocontrast media
Co-existing conditions:
- HIV, EBV, CMV, CF increase the likelihood
Chronic urticaria or mastocytosis:
- May be sensitive to NSAIDs, opioids and drugs with histaminergic properties
Drug dependent factors:
- Penicillin/Beta-lactams, muscle relaxants, radiocontrast media, NSAIDs, high molecular weight starches, chlorhexidine, opioids
Frequent and prolonged doses:
- The more a patient is exposed to a drug, the more likely they will develop an allergy to it
Gender:
- F>M
How do you manage patients with an allergy history who require contrast?
Premedication with corticosteroids and antihistamine
What consists of a mild allergic drug reaction and how do you manage it?
Itching, widespread urticaria, N+/-V, nasal congestion/sneezing
- In the absence of feelings of throat swelling/resp. difficulties, tachycardia, hypotension or neurological symptoms
Treat with PO chlorphenamine 4mg
But observe - as could progress to severe response
