Anaphylaxis Flashcards
Anaphylaxis - Definition
Severe and rapid allergic reaction w/ symptoms and signs of airway edema, asthma or hypotension
Goal of Care
Prompt treatment and transportation to hospital
Overview
Allergic reactions occur b/c cells in the system recognize a protein as “foreign”
Cells degranulate and release a number of factors including histamine.
Histamine and other factors cause a cascade of events at the cellular level resulting in:
- tissue edema
- smooth muscle relaxation
which results in capillary leakage and inability to vasoconstrict leading to hemodynamic collapse
Death occurs secondary to airway obstruction from tissue edema and hemodynamic collapse
Rash/Hives/Urticaria
Most, but not all patients with anaphylaxis develop a rash (80%)
A pt with urticaria that has been present for > 30 minutes and not associated with any other symptoms of anaphylaxis, is less likely to develop anaphylaxis and may not require treatment in the pre-hospital setting.
However, reactions are unpredictable and require high level of concern.
Conversely, while rapid development of hives may be the first sign of impending anaphylaxis not all patients with anaphylaxis have hives. 20% never develop hives, and some develop other symptoms such as airway compromise or hypotension before hives develop.
Many episodes of hives are NOT anaphylaxis, but instead idiopathic urticaria. If the hives have been present for more than one day, they are almost never due to anaphylaxis.
SOB/Wheeze
Difficulty speaking or breathing is an ominous sign in anaphylaxis, indicative of airway involvement
Hypotension
Hypotension is an ominous sign of severe anaphylaxis; indicative of hemodynamic collapse
Gastrointestinal Symptoms
Abdo pain, nausea, vomiting and occasionally diarrhea are GI manifestations of anaphylaxis
These often go unrecognizeds as symptoms of anaphylaxis
Distinguishing Idiopathic Urticaria from Anaphylaxis - Duration of hives
- Days (sometimes on and off) “did you have hives earlier this week?”
vs.
- Never lasts more than 4 hours
Idiopathic Urticaria vs Anaphylaxis - History of previous anaphylaxis
- Usually no
vs.
- Often
Idiopathic Urticaria vs Anaphylaxis - Clear association w/ trigger
- “not sure what caused this”
vs.
- Yes - reaction always within 4 hrs, usually within first 30mins
Idiopathic Urticaria vs Anaphylaxis - Other symptoms
- Upper respiratory tract infection symptoms +/- fever
vs.
- Any of: Watery runny eyes, nose, sneezing, itchy or swollen tongue, coughing, drooling, voice change, stridor, wheeze, vomiting, diarrhea, abdominal pain, increased work of breathing, syncope, sudden fatigue, decreased LOC, feeling sudden impending doom or abdominal cramping
Idiopathic Urticaria vs Anaphylaxis - Management
- Oral Benadryl (not indicated by BCEHS TGs)
vs.
- EPI IM in lateral thigh - repeat dosing given q 5min if not improving.
- Ventolin can be used once EPI given for resp distress
- Benadryl IV can be considered ONLY as a 3rd line drug by ACPs/CCPs and its administration should not interfere with Q5min Epi usage, Ventolin or ABC management.
Guiding Principles - Exposure
Most pts w/ anaphylaxis have a hx of allergic reaction and know what they have been exposed to, but this is not always the case
In rare cases, reactions may develop later (e.g. as late as 4 hours) after exposure to an allergen. Late-phase or biphasic reactions occasionally occur 4 - 12 hours after the initial attack, especially with oral ingestions
Guiding Principles - Special Note 1
Patients with symptoms of airway compromise from edema (difficulty swallowing, swollen tongue, hoarse voice), bronchospasm and/or hypotension are at significant risk of death and require consideration for immediate treatment in the field.
Guiding Principles - Patient Positioning
Patient positioning is important. Patients should be supine with legs elevated, except in those who cannot tolerate supine positioning due to respiratory distress. Sitting upright or standing has been associated with fatal allergic reactions.
Guiding Principles - Epinephrine
EPINEPHrine is the primary treatment and is usually effective very rapidly. Intra-muscular injection in the mid lateral thigh (vastus lateralis) is the required route of administration. IM injection in other muscle groups (Deltoid etc.) or subcutaneous injection has approximately 6 times lower peak serum concentrations of EPINEPHrine. Repeat doses of EPINEPHrine should ideally be given in alternating thighs as vasoconstriction may affect absorption.
Guiding Principles - Diphenhydramine
Diphenhydramine (anti-histamine “Benadryl”) is NOT effective in life threatening anaphylaxis and has a delayed onset of action and should not be administered instead of EPINEPHrine. Antihistamine use is to address comfort measures only when a patient has idiopathic urticaria. Its use or administration will not significantly alter outcomes, and may distract from management with EPINEPHrine and ABC’s.
Guiding Principles - Special Note 2
Benadryl is not effective in angioedema, cardiovascular, gastrointestinal or respiratory symptoms therefore is considered a second line therapy at most; oral use is usually adequate. EPINEPHrine is your treatment drug. IM Benadryl is not indicated.
Causes
It is possible to be allergic to anything. Do not dismiss the patient who claims an allergy that seems unusual.
The most common causes of anaphylaxis include:
- Insect bites (yellow jackets, wasps);
- Foods: priority allergens in Canada
peanuts, tree nuts, seafood (shellfish & fish) milk, egg, wheat, sesame, soy, mustard
- Drugs/medications
- Latex
- Immunotherapy injections/vaccinations
Isolated Angioedema
Rarely you may see swelling of face/neck/oral cavity/airway without any other signs of anaphylaxis.
This may be seen in combination with ACE type antihypertensive medication or in rare “Hereditary Angioedema”.
If in doubt, treat as anaphylaxis but if you suspect this call CliniCall immediately to discuss management
Intervention Guidelines - EMR
Position spine
Remove allergen (scrape off stingers/stop drug)
Supp O2 - consider noDESAT via nasal cannula for persistent hypoxia
Intervention Guidelines - PCP
To reduce angioedema (lips tongue airway); increase blood pressure and circulation; bronchodilate
- EPI 0.3 - 0.5mg 1:1000 IM q 5mins x 3
For bronchodilation (only to be used AFTER EPI, if no other systems involved - i.e pt has isolated bronchospasm) - Salbutamol 5mg neb - repeat if necessary
Correct hypo-perfusion - hypotension BP <90mmHg
- Fluid challenge (if no pulmonary edema)
N/S up to 2Ls - reassess BP and lungs every 500 cc - target 90 systolic
Intervention Guidelines - ACP
All above plus
If refractory to other forms of EPI
- EPI 50-100mcg 1:10,000 IV in increments to effect (max dose 0.5mg)
Persistent hypotension despite fluids/EPI in pts on ACE inhibitors/ B blockers
- Glucagon 1-2mg IV q 5 mins; mandatory EPOS consult
Mitigate medium term effects and decrease histamine response
- Diphenhydramine 25-50mg IV
- Intubation as per Adult Induction Guidelines
- Cricothyrotomy, if unable to oxygenate and ventilate
Further Care
- Corticosteroids
- Antihistamines
- Preventative measure including EPI auto injectors, antihistamines or prophylactic steroids
