Anaphylaxis is a severe immune reaction to a particular antigen. It is a type I mediated allergic reaction i.e. driven primarily by histamine and prostaglandins.
Pathophysiology
- Anaphylaxis is an IgE mediated hypersensitivity reaction caused by exposure to a particular antigen i.e. it is a type I hypersensitivity reaction.
- Mast cells and basophils degranulate in response to the antigen, causing release of various immune mediators including histamine, tryptase, prostaglandins and leukotrienes.
- These immune mediators cause smooth muscle contraction, peripheral vasodilation and increased vascular permeability (resulting in fluid extravasation) which ultimately results in airway oedema, bronchospasm, hypotension, hypoxia, oedema and erythema. An eosinophilia can also be seen in these patients.
Causes
- Food allergy e.g. peanuts, walnuts, almonds, strawberries, fish
- Stings e.g. wasps or bee stings
- Drugs e.g. antibiotics (co-amoxiclav, teicoplanin, penicillins, cephalosporins), NSAIDs, chlorhexidine
- Latex
- Contrast media
Clinical Features
Onset is very acute, and features tend to occur within minutes of exposure to an allergen. Patients can present on a spectrum from a mild reaction to severe anaphylactic shock requiring urgent treatment. Specific clinical features include:
- Dyspnoea
- Feeling of something in the throat/feeling like the throat is closing up
- Wheeze
- Hoarse voice
- Stridor
- Hypotension
- Drowsiness or confusion
- Anxiety/sense of impending doom
- Cyanosis/Pallor
- Clammy
- Nausea, vomiting or diarrhoea
Skin changes are also very common with anaphylaxis and include the following:
- Pruritis
- Raised wheals
- Urticaria
- Angioedema
- Orbital oedema
- Erythema
Boussetta N1*, Ghedira H2, Hamdi MS1, Ariba BY1, Metoui L1, Ghasallah I1, Zriba S2, Louzir B1, Msaddak F2, Ajili F1 and Othmani S11 - Department of Internal Medicine, Military Hospital of Tunis, Tunisia2 - Department of Hematology, Military Hospital of Tunis, Tunisia, CC BY 4.0 , via Wikimedia Commons https://upload.wikimedia.org/wikipedia/commons/3/37/Angioedema_of_the_face.jpg
Angioedema of the Face
Red Flags
- Rapidly progressing symptoms
- Airway compromise
- Systemic upset e.g. tachycardia, hypotension, desaturating, vomiting, abdominal cramps
- Confusion or Drowsiness
Differential Diagnosis
- Sepsis: Raised white cell count or features of infection may lead you to consider sepsis as opposed to anaphylaxis.
- Acute asthma attack
- Hereditary angioedema: Patient may have had previous angioedema attacks in the past
- Scromboid poisoning: Occurs when someone eats fish (tinned, fresh etc) which has high levels of histamine as a result of poor storage. This is not an allergic reaction, and patients are able to eat that particular fish again, but the symptoms can mimic anaphylaxis.
- Panic attack: Particularly if a patient who has had an anaphylactic reaction in the past feels they have been re-exposed to the offending allergen.
Investigations
- Full blood count: May see an eosinophilia
- Tryptase concentration: Tryptase is a component of the secretory granules of mast cells, are rises in anaphylaxis. Three samples as typically taken:
- As soon as possible
- 1-2 hours after symptoms begin (no later than 4 hours)
- 24 hours or during follow-up to gauge a baseline level of tryptase
Management
Anaphylaxis is a serious condition requiring urgent treatment. An A-E approach (Airway, Breathing, Circulation, Disability and Exposure/Everything else) is generally used to approach the acute patient.
However, adrenaline is the mainstay of treatment and should be administered immediately if anaphylaxis is diagnosed prior to starting any other treatments. UK Resuscitation Council guidelines advise the folloiwng for adults over the age of 12:
- Stop the Trigger: If patients develop an anaphylactic reaction shortly after being administered a drug, immediately stop the drug/suspected infusion. Additionally, patients who have been stung should have the stinger removed.
- Initial Management: Give IM adrenaline 1:1000, 500 micrograms IM, into the anterolateral aspect of the middle third of the thigh
- No Response After 5 Minutes: Repeat IM adrenaline and give IV fluid bolus of 500mL-1L 0.9% saline IV or 10ml/kg for children
- No Response Despite Repeat Adrenaline: Start an adrenaline infusion of 1mg (1ml of 1mg/ml 1:1000 adrenaline) in saline. IM adrenaline should be repeated every 5 minutes until the adrenaline infusion has been set up.
Other Drugs
- Nebulised Adrenaline: Can be used as an adjunct to help laryngeal oedema. Usual dose if 5ml of 1mg/mL nebulised.
- Antihistamines: Antihistamines are no longer recomended as part of initial first-line management of anaphylaxis but they can be used to treat the skin symptoms of anaphylaxis. A non-sedating oral antihistamine e.g. cetrizine can be used, usually at a dose of 10-20mg for adults.
- Steroids: Again, steroids are no longer recommended in the emergency treatment of anaphylaxis, but their use can be considered for refractory reactions or ongoing symptoms.
- Glucagon: In patients treated with beta-blockers, adrenaline might not be as effective. Glucagon can be considered in these cases (glucagon is used as an antidote in beta-blocker overdose) to help, particularly where adrenaline is not giving an adequate response.
A-E Pathway
- Airway:
- Ensure the airway remains patent
- An airway adjunct can be inserted e.g. nasopharyngeal/oropharyngeal
- Intubation may be needed if the patient is deteriorating
- Consider an adrenaline nebuliser to help with airway oedema
- Breathing:
- Monitor oxygen saturation
- Administer nebulised beta-2 agonists e.g. salbutamol alongside oxygen
- Circulation:
- Monitor blood pressure: Monitor for anaphylactic shock
- Monitor ECG: Anaphylactic shock can result in myocardial ischaemia
- Gain IV access
- An ABG may be useful, particularly if the patient is hypoxic
- Adrenaline 1:1000 IM 500 micrograms to reverse vasodilation and bronchospasm.
- If indicated, IV fluids can be administered e.g. 0.9% saline 500ml-1000ml. This is usually given in the anterolateral aspect of the thigh.
- Monitor ECG
- Take routine bloods e.g. FBC, U&Es, CRP
- Disability:
- Check GCS, blood glucose and pupils (anaphylaxis can cause a hyperglycaemia)
- Exposure/Everything else:
Discharge
Patients should be observed for up to 24 hours following an anaphylactic reaction, particularly as it is possible for patients to develop a ‘rebound’ anaphylaxis following initial recovery – this is known as a biphasic reaction. Patients should be considered for an Epipen to take home, and there should be a plan in place for follow-up and informing the patient’s GP of the anaphylactic reaction.
References
https://www.ncbi.nlm.nih.gov/books/NBK482124/
https://www.resus.org.uk/sites/default/files/2021-05/Emergency%20Treatment%20of%20Anaphylaxis%20May%202021_0.pdf
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3314039/
