Anaphylaxis & Angioedema Flashcards
What is anaphylaxis?
Severe, life threatening allergic reaction leading to compromise of airway, breathing or circulation.
*Bold is key difference between allergic reaction and anaphylaxis
Discuss the pathophysiology behind anaphylactic shock
- Type 1 hypersensitivity reaction
- See image. Idea that individual already been sensitised to antigen; upon reexposure antigen binds to and crosslinks two IgE antibodies on mast cell surface causing degranulation and release of mediatiors such as histamine
State the symptoms & signs of anaphylaxis
- Dyspnoea
- Wheeze
- Stidor
- Chest tightness
- Cyanosis
- Laryngeal obstruction
- Urticaria
- Angioedema
- Erytheama
- Itching
- Sweating
- Abdo pain
- Tachycardia
- Hypotension
- D&V
How long, following exposure to trigger, does anaphylaxis occur?
Within minutes
What kind of shock can anaphylaxis lead to and why?
Distributive shock: release of histamine from mast cells causes vasodilation, decrease TPR
State some common triggers for anaphylaxis
- Insect bites
- Food
- Medications
Discuss the immediate management/treatment of anaphylaxis
Remove the cause if still there and do A-E assessment:
- Airway: secure airway
-
Breathing:
- Oxygen
- Salbutamol if required (5mg nebulised)
- Adrenaline nebulised if laryngeal oedema
-
Circulation:
- Passive leg raise
- Intramuscular adrenaline 0.5mg (0.5mL of 1:1000, 0.5mg of 1:1000)
- IV chlorphenamine 10mg & hydrocortisone 200mg
- IV bolus of 0.9% saline (500ml over 15 min)
-
Disability:
- Lie pt fla to improve cerebral perfusion
-
Exposure:
- Look for other signs of anaphylaxis, flushing, urticaria, angioedema
…Consider ITU involvement if not improving
Three medications can also be given for anaphylaxis:
- Intramuscular adrenaline: can repeat after 5 minutes
- Antihistamines e.g. chlorphenamiine or cetirzine
- Steroids e.g. IV hydrocortisone
For the three medications that can be used in anaphylaxis, state how they work
-
Intramuscular adrenaline injection:
- Vasoconstriction: adrenaline has a higher affinity for B2 receptors at physiological levels, however at higher levels it also binds to A1 to cause vasoconstriction- increase blood pressure
- Bronchodilation: bind to B2 receptors in lungs to cause smooth muscle bronchodilation
- Increase myocardial contraction: adrenaline bind to B1 in heart
- Inhibits mast cell activation
- Antihistamines e.g. chlorphenamine or certrizine: block H1 receptors preventing actions of histamine
- Steroids: ?reduce inflammation. ?reduce risk biphasic attack?
State the doses of each of the following medications to be used in anaphylactic shock:
- Nebulised salbutamol
- IM adrenaline
- IV hydrocortisone
- IV chlorphenamine
- Nebulised salbutamol 5mg
- IM adrenaline 0.5mg
- IV hydrocortisone 200mg
- IV chlorphenamine 10mg
Discuss the later/further/post-immediate management of anaphylaxis
- Admit to ward
- Monitor ECG
- Continue chloramphenamine 4mg/6hr PO if itching
- Suggest MedicAlert bracelet
- Teach about self injected adrenaline
- Skin prick tests to identify allergens to avoid
Within what time scale must serum mast cell tryptase be measured following anaphylactic shock?
Must be measured WITHIN 6 HOURS (as it only stays in blood for ~6hrs)
*Common exam Q
Adrenaline auto-injectors are given to all pts with anaphylactic reactions; however, they are also sometimes given to other pts with generalised allergic reactions. State some situations in which you would give an adrenaline auto-injector to a pt who doesn’t have anaphylaxis
- Asthma
- Poor access to medical treatment (e.g. rural location)
- Adolescents (higher risk)
- Nut or insect sting allergies
- Significant comorbidities e.g. cardiovascular disease
Describe how you use an adrenaline autoinjector
- Remove saftey cap on non-needle end
- Grip the device in a fist with needle pointing downwards (needle end is orange or black)
- Firmly jab device into outer portion of thigh until device clicks (this can be done through clothing)
- Hold device for 3secs (EpiPen advice) or 10s (Jext advice) before removing it
- Remove device and massage area for 10sec
- Phone emergency ambulance
- Second dose may be given after 5 mins
Summary of Resus council anaphylaxis pathway
When would you start/follow the refractory anaphylaxis algorithm?
Tried two doses of IM adrenaline and no improvement in respiratory or cardiovascular symptoms
Discuss the refractory anaphylaxis algorithm
Discuss the ongoing management of anaphylaxis after stabilisation
- Antihistamines
- Corticosteroids (NOTE: routine use of corticosteroids to treat anaphylaxis is not advised. Consider giving steroids after initial resuscitation for refractory reactions or ongoing asthma/shock.
- Other medications (e.g. bronchodilators if needed)
