Anaphylaxis (Resp) Flashcards
BTW the reason anaphylaxis ends up happening is bc of lots of factors, e.g. possible genetic predisposition
Define anaphylaxis
It is a severe systemic Type 1 IgE-mediated hypersensitivity (allergic) reaction that is rapid in onset and may cause death.
It is a life threatening medical emergency.
List the features of anaphylaxis definition
Severe, life threatening type 1 hypersensitivity reaction.
IgE-mediated
Rapid onset + systemic.
Occurs when exposed to certain precipitants.
Give examples of what could cause anaphylaxis
Precipitants that can cause anaphylaxis in certain individuals include:
Medications e.g. ABs like penicillin, NSAIDs
Certain foods (e.g. peanuts and eggs)
Bee or other insect stings
Describe the first stage of the pathophysiology of anaphylaxis
Sensitisation phase
1. First exposure to allergen either by ingestion, inhalation, skin contact etc.
2. Dendritic cells will process and present them to naive T cells which will activate and then differentiate into Th2 cells in response to IL-4 (cytokine given by eosinophils, basophils etc but not from the DC that much)
3. B cells encounters the allergen, internalises and presents the allergen to the Th2 cells which produce IL-4 to the B cells (also release IL-5,13)
4. This causes B cells to class switch from IgG to IgE producing B cells
5. These allergen specific IgE antibodies diffuse throughout the body and bind to high affinity receptors (FcεRI) on mast cells and basophils via Fc, leaving their Fab exposed and free for the allergen.
6. This sensitises the cells to the allergen, so upon next exposures they will react
Describe the second stage of the pathophysiology of anaphylaxis
Effector phase
1. Upon second exposure to the same allergen, it binds to and cross links IgEs on the Mast Cells and basophils
2. This triggers the release of pro inflammatory mediators from the cells known as degranulation
4. The main IMs released are histamine, tryptase, LTs, PGs.
5. These cause: vasodilation, increased vascular permeability, smooth muscle contraction, and mucus secretion, leading to the clinical manifestations of anaphylaxis.
What is the biphasic reaction in hypersensitivity reactions/anaphylaxis?
This describes the recurrence of anaphylaxis symptoms soon after the initial episode.
It happens in about 5% of pts (~12 hrs after but may occur over 24 hours after). It is usually less severe.
Main cell is eosinophils degranulating.
a.k.a late-phase reaction
What are the risk factors of anaphylaxis?
History of anaphylaxis
Atopy (genetic tendency to develop allergic diseases) tf so if diagnosed with Asthma, atopic dermatitis etc.
Family history
What are the risk factors for a biphasic reaction?
Severe initial presentation
More than one dose of adrenaline required
Delay in giving adrenaline (>30-60 minutes from initial symptoms)
How is anaphylaxis diagnosis confirmed - investigation?
This is by measuring the serum levels of mast cell tryptase.
However, this is done after the patient is stabilised.
How is anaphylaxis recognised, list the symptoms)?
ABCDE approach/assessment
Airway (oedema): swelling of throat and tongue leading to hoarse voice and stridor, cant swallow/breathe
Breathing (bronchospasm): wheeze, dyspnea, hypoxemia -> cyanosis
Circulation: signs of shock - dizzy, pallor, clammy, tachycardia, ow BP with feeling of faint/dizzy or collapse, decreased consciousness
Disability (altered neurological status): confusion, agitation, loss of consciousness (caused by ABC bc it causes hypoxia, hypercap, cerebral hypoperfusion). sense of ‘doom’
Exposure (skin or mucosal changes): widespread erythema + urticaria, itchy, angioedema in eyelids/lips (often first features)
However, just skin or mucosal changes without ABC does not suggest an anaphylactic reaction.
GI signs incl: abdo pain, incontinence + vomiting are also common
How is suspected anaphylaxis managed - emergency management?
Urgent ABCDE assessment
Call for help (e.g. 999, resus team)
Remove trigger and position patient - lay flat with/without legs raised. Lie left side if pregnant
Give IM adrenaline. If no response, repeat IM adrenaline after 5 minutes. Keep doing until improvement.
High flow O2 and monitoring (pulse oximetry, ECG, BP)
If the patient is hypotensive/shock - do IV fluid challenge using crystalloid.
How is IM adrenaline administered in anaphylaxis?
Injected at anterolateral aspect of middle third of the thigh
What is the management after the patient is stabilised in anaphylaxis?
May give anti histamines to help skin symptoms - this used to be part of initial management, but NOT anymore (done once stabilised via adrenaline/IV fluids)
Patients should be monitored for 6-12 hours after the initial presentation in case of a rebound episode (Biphasic reaction)
All pts with a new diagnosis should be referred to a specialist allergy clinic
Patients should be prescribed 2 adrenaline auto-injectors and trained how to use it
List the types of patient discharge in anaphylaxis (after management)?
Fast track discharge - discharge after 2 hours observation from anaphylaxis resolution
Discharge minimum 6 hours ‘’
Discharge minimum 12 hours ‘’
When is fast track discharge done in anaphylaxis?
Patients can be discharged 2hrs after symptom resolution if:
- good response within 5-10 mins to a single dose of adrenaline
- complete resolution of symptoms
- pt has been given an adrenaline auto-injector and is trained how to use it
- adequate supervision following discharge
