Derm - Anaphylaxis

Question 1

Defintion

Answer 1

Medical emergency and characterised by rapid onset, life-threatening airway, breathing and circulatory compromise.
- Severe, systemic hypersensitivity reaction.

Question 2

Allergic reaction

Answer 2

Not life-threatening and presents with milder symptoms without cardio respiratory compromise

Question 3

Epidemiology

Answer 3

History of atopy: such as asthma, eczema, or allergic rhinitis
Previous anaphylactic reaction
Higher socioeconomic status

Question 4

Pathophysiology

Answer 4

Exposure to an allergen causes the susceptible individual to form specific IgE antibodies.
Subsequent exposure leads to IgE -mediated activation and degranulation of mast cells , whilst basophils release inflammatory mediators such as histamine, prostaglandins, and leukotrienes ( type I hypersensitivity reaction ).
This results in rapid vasodilation and an increase in vascular permeability causing leakage of fluid out of the intravascular compartment.
Ultimately, this leads to cardiovascular collapse , sometimes referred to as anaphylactic shock.
Additionally, bronchospasm and mucous membrane secretion result in respiratory distress and life-threatening laryngeal oedema .

Question 5

Criteria for anaphylaxis

Answer 5

• Sudden onset and rapid progression of symptoms
• ABC = Airway and/or Breathing and/or CIrculation problems
• Skin and/or mucosal changes (flushing, urticaria, angioedema) but these may be absent in up to 20% of cases

Question 6

Signs

Answer 6

Hypotensive and tachycardic
Tachypnoeic
Urticarial rash

Question 7

Symptoms

Answer 7

Exposure to allergen
Angioedema: swelling of the face, tongue, larynx, resulting in difficulty in breathing
Strider and wheeze
Pruritus and rash
Dizziness
Syncope

Question 8

Diagnosis

Answer 8

Immediate treatment is the absolute priority for suspected anaphylaxis

Primary investigations
- Mast cell tryptase: measured on 3 occasions = immediately after treatment has commenced, at 1-2 hours post-reaction and after 24 hours post-reaction
- Elevated level will be seen up to 12 h after an anaphylactic reaction and return to baseline at 24 hours
- If a level cannot be taken at 24 hours = a sample can be taken at a follow-up allergy clinic instead

Question 9

Treatment

Answer 9

FIRST LINE = Adrenaline IM - Best in the anterolateral aspect of the middle third of the thigh
- repeat IM adrenaline after 5 minutes if airway/breathing/circulation problems

Other:
- Non sedating oral antihistamines: in preference to chlorophenamine, may be given following initial stabilisation especially in parent with persisting skin symptoms (urticaria or angioedema)

Question 10

Refractory anaphylaxis

Answer 10

Anaphylaxis where there is no improvement in respiratory or cardiovascular symptoms despite two appropriate doses of IM adrenaline
- IV fluids: must be given early if hypotension or shock is present
- IV adrenaline infusion
- IV hydrocortisone: must be considered but Resuscitation Council UK say no evidence for or against the use for refractory anaphylaxis.

Question 11

Discharge

Answer 11

Fast track discharge (after 2 hrs obs from resolution of attack:
- good response (within 5-10 mins) to single dose of adrenaline within 30 mins of onset = AND
- complete the resolution of symptoms AND
- The patient already has unused adrenaline auto-injectors and has been trained how to use them AND
- Adequate supervision following discharge

Minimum 6 hours observation after resolution of symptoms recommended if:
- 2 doses of IM adrenaline needed to treat reaction OR
- Previous biphasic reaction

Observations for at least 12 hours following resolution of symptoms if any ONE the following:
- severe reaction requiring >2 doses of adrenaline
- Px has severe asthma or reaction involved severe respiratory compromise
- possibility of continuing absorption of allergen e.g. slow-release medicines
- Px presents late at night, or may not be able to respond to any deterioration
- Px in areas where access to emergency care is difficult

Question 12

Follow up prescribing on discharge

Answer 12

• Referral to an allergy specialist : for all patients, to identify the cause and reduce the risk of recurrence
• Adrenaline auto-injector/EpiPen: upon discharge all patients should have two devices available at all times in case of recurrence in the future; training of patients and those close to them (family, friends etc.) is vita

Question 13

Complications

Answer 13

• Cardiac arrest : occurs due to cardiac ischaemia secondary to anaphylaxis-associated hypotension or adrenaline-induced hypertension and tachycardia
• Biphasic reaction : an additional anaphylactic reaction occurring between 1 and 72 hours after the initial symptoms
  = Recurrence : a previous episode of anaphylaxis correlates with an increased risk of a future anaphylactic reaction