Allergy, hypersensitivity and anaphylaxis Flashcards
Define urticaria, angio-oedema and anaphylaxis
Urticaria - common allergic reaction to foods, drugs or physical stimuli characterised by an erythematous raised and pruritic rash
-spontaneous episdoes lasting less than 6 weeks are considered acute those loner are considered chronic
Angio-oedema
It is a result of abrupt vasodilation and increased vascular permeability allowing fluid to move from the vascular to intestinal space. As the swelling is located in the deeper layers of the skin the appearance is often normal in colour and patients may complain more of a pinr of pressue
1) Allergic mechanism in reponse to exposure to foods, drugs, physical stimuli
2) Non allergic mechanism (hereditary angio (c1 esterase defiency), or bradykinin induced)
3) idiopathic
Anaphylaxis
- an acute onset illness with typical skin features (urticaria, or erythema/flushing and or angioedema) plus involvement of respiratory and/or CVS and/or persistent severe GIT symtpoms or
- Any acute onset of hypotension, bronchospasms or upper airway obstruction where anaphylaxis is considered possible even if typical skin features are not present
Describe types of hypersensitivity reaction
Type 1 - immediate hypersensitivity
- IgE mediated and account for most allergic and anaphylactic reactions
- exposures to sensitizing allergens causes mediators from mast cells and basophils to be released
Type 2- Cytotoxic antibody reaction
-Antibody mediated cytotoxic reaction. Complement fixing IgG or IgM engages cell bound antigen activating the classic complement pathway and leading ot the fixation of membrane attack complexes on the cell surgace and subsequent cell lysis.
Type 3- immun complex
IgG and IgM complex mediated. Circulating solble antigen antibody immune complexes migrate from the circulation to be deposited in ht perivascular interstitial spcae thereby activating the complement system.
Type 4 - delayed hypersensitivyt
List risk factors for develepment of anaphylaxis
Age and sex
- pregnant women, infants, teenagers, elderly
Route of admin
-Parenteral >oral
higher social economic status
Time of the year
History of atopy Emotional stress acute infection physical exertion history of mastocytosis
List factors linked to severity of anaphylaxis
- Extremes of age
- Co-morbid conditionss
- —CVS (heart failure, IHD, hypertension)
- — Pulmonary disease (ashtma, obstructive airway disease)
Others
- Cocurrent use of antihypertnesive agents specifically beta blocker or ACE
- recent anaphylaxis episode
In general the rapidity of onset of anaphylaxis is correlated with the severity
List criteria for diagnosis of anaphylaxis
Anaphylaxis is highly likley when any of the following 2 criteria are fulfilled
1) Criteria 1
- Acute onset illness (minutes to several hours) with simultaneous involvment of the skin, mucosal tissue or both and at least one of the following
a) respiratory compromise (e.g dyspnoea, wheeze, bronchospasm, stridor, reduced peak expiratory flow, hypoxemia)
b) reduced BP or associated symptoms of end organ dysfunction (hypotonia, syncope, incontinence)
c) severe gastrointestinal symptoms (e.g severe crampy abdominal pain, repetitive vomiting) expecially after exposure to non food allegen
2) criteria 2
- ACute onset of hypotension or bronchospasms or laryngeal involvement after exposures to knonw or highly probable allergen for the patients (minutes to several hours) even in the absence of typical skin involvment
Discuss clinical manifestations of anaphylaxis
Resp
- upper - rhinitis, layrngeal oedema
- lower -bronchospasm
CVS
- Circulatory collapse
- dysrythmias
- Cardiac arrest
Skin
- urticaria
- angioedema
Eye
-conjunctivitis
GIT
-vomiting, diarrhoea, cramoing
Misc
-sense of impending doom, headache, confusion
Haem
-DIC
Describe management of anaphylaxis
Emergency measures taken simultaneously
1) remove trigger if possible
2) supine position + monitoring - upright positioning can be fatal
3) large bore IV
4) preparation for intubation with expectance for difficult airway
- awake fibreoptic
- surgical
5) fluid: — marked fluid extravasation into the tissues can occur do not forget fluid resus !!!
- adults 1000mls in the first 5 minutes
- paeds 20-30ml/kg
Adrenaine
- first line
- 500 mic IM adrenaline injected into the outer mid thigh
- 10mic/kg for children up to 500mic
- > 12 years of age or >50kg epipen adult
- Infant greater than 7.5kg can be treated with epipen juniour wihtout ill effect
- Can be repeated every 5 minutes if given second dose should consider drawing up adrenaline infusion 0.05mic/kg/min
- Can make drip bag by placing 1 ml of 1:1000 adrenaline into a liter of nacl – giving consentration of 1mic/ml - start at 5ml/kg/min (0.1 mic/kg/min)
Additional measures if infusions is ineffectiv
1) upper ariway obstruction
- Consider neb adrenaline for upper airway obsturction
2) Persistant shock
- fluid up to 50ml/kg in the first 30 minutes
- glucagon 1-2mg in adults or 20-30mic/kg in children /HIET – specifically if taking beta blockade
3) persistnat wheeze
- salbuatmol
- Corticosteroids
A: adjuncts, intubation if needed predict difficult airway do not make prolonged attempts may need surgical
B: o2 to maintain spso2 >94 - bronchodilator or inhaled adrenaline if infusion not wokring
C: fluids resus is important due to signicant third spacing, adrenaline as above, consider HIET/glucagon in patient on B blocker may need dual pressor. Antihistamines and steroids show no benifit in acute management of anaphylaxis
Resus in cardiac arrest
- Massive vasodilation and fluid extravasation
- Unilikley IMI adrenaline will be absorbed in this situation and will require IV
- agressive fluid resus 50ml/kg in 30 minutes monitoring for overtreatment
- ddo not give up to soon - this is a situation in which prlonged CPR should be considered as the patient arrest rapidly with previously normal tissue oxgenation and has a potentionally reversible cause
Discuss disposition of anaphylactic patients
Up to 20% of patients may experience a biphasic reaction defined as a reoccurrence of symptoms wihtout re-exposure to the triggering agent.
Most of these reaction occur wihtin 8 hours but have been reported as far out as 72 hours.
Patients who respond to treatment and experience complete resolution of symptoms can be dsicharged home after an observation period of 4-8 hours. Consider extended observation or hospitalization of patients who
1) present with protracted anaphylaxis, hypotension or airway invovlement
2) Receive IV epinephrine or more than 2 doses of IM epineprhine
3) have poor OPD social support
Patient should no how to use epipen and leave with prescirpition for 2 autoinjectable pens – ideally filled in the department.
- hold in fist midway - nil finger or thumbs at eitehr end. remove blue cap
- hold leg still and place orange end against outer mid thigh (with or without clothing)
- push down hard until a click is heard or felt and hold for 3 seconds remove EpiPen
Discuss management of non allergic angio-oedema
These do not respond to treatment with epinephrine antihistamines or steroids. - IN life threatening situation airway compromise may necessitate intubation with predicted difficult airway
FFP which contains CI inhibitor has been reported to be effective in abolosing acute attacks.
C1 inhbitor consentrate is afiable the dose is 20units/kg IV
Discuss the mechanisms for HAI and ace inhibitor induced angio-oedema
HAI consists of CI esterase inhbitor defieicny which leads to activation of the kallikrien-kinin system increasing the consumption of kninongen resulting in increased production of bradykining.
In the setting of ACE inhibitor induced the inhibition of ACE one of the main inactivators of bradykinin results in increased bradykinin levels.
Describe Serum sickness
Type 3 hypersensitivity reaction
Signs and symptoms of serum sickness being one to two weeks after the first exposure of the responsible agent. IN those who ahve been previously expsed the syndrome starts earlier and the illness has a more severe and explosive onset
Cinical features
1) fever is almost universal usually >38.5 - rigors unusual
2) dermatological finding
- Pruiritic rash which is often the earliest clinical features. The dermatitis generally lasts a few days to two weeks after agent has been stopped.
- MM are not involved -
- may be urticarial lesions which are typically longer lasting than hives from other causes
3) rheumatic features
- arthralagia are a characteristic but inconsistent feature of serum seikcness
4) less common features
- non specific headache and blurred vision
- oedema
- lymphadenopathy
- splenomegaly
- anterior uveitis
- peripherial neuropathy including GBS
Most cases can be treated symptomatically after removal of offending agent
For sever symptoms - steroids are helpful
