Emergency Medicine Bite-Sized Basics
- Multisystem severe hypersensitivity reaction of sudden onset (or rapidly progressive).
- Requires at least 1 of the following 3 criteria:
- Acute onset of mucocutaneous signs AND 1 of the following:
- respiratory compromise (wheezing-bronchospasm,
- dyspnea, stridor, hypoxemia),
- ↓BP (syncope),
- Rapid onset of 2 of the following after exposure to likely allergen:
- mucocutaneous signs,
- respiratory compromise,
- persistent gastrointestinal symptoms.
- Hypotension after exposure to a known allergen.
- Allergic: Type 1 hypersensitivity reaction: allergen crosslinks specific IgE antibodies on mast cells and basophils → rapid release (degranulation) of stored histamine, LTs, PAF, cytokines & chemotactic factors →capillary leakage, mucosal oedema →ultimately shock and asphyxia. Usually immediate (<1hr), occasionally biphasic & rarely delayed.
- Anaphylactoid: degranulation via non-IgE mediated pathway.
- Foods: (peanuts, other nuts, shellfish, fish, eggs, milk, strawberries, mushrooms)
- Venom: (bee/wasp stings) or antivenoms
- Drugs (incl Abx, opioids, NSAIDs, IV contrast, muscle relaxant, streptokinase)
- Others: Latex, heat/cold, exercise.
- History: Previous reaction, new exposure to a drug / food.
- Mucocutaneous: Urticaria, rhinitis, conjunctivitis and angio-oedema.
- Respiratory: itching of the palate / external auditory meatus, dyspnoea, stridor / wheezing.
- CVS: Palpitations, tachycardia, hypotension, syncope, collapse
- GIT: Nausea, vomiting, abdominal pain, diarrhoea
- Other: Sense of impending doom
- Attach monitoring, take vital signs, ECG.
- Remove allergen, sting, wash mouth out etc.
- Airway: Consider suction, intubation (adrenaline 1:1000 5ml neb may help if poor view, but don’t delay if worsening) – beware hypotension may be exacerbated with drugs.
- CPR if cardiac arrest
- High flow O2
- 0.3–0.5mg (0.3–0.5ml of 1:1000) [child 10mcg/kg or 0.01ml/kg 1:1000] IM stat
- If unresponsive to 2 x IM doses or moribund, consider IV options:
- Bolus of 0.1ml/kg 1:100,000 IV over 5–10min [1mcg/kg]
- Dilute 1ml of 1:10,000 [100mcg] in 10ml NS to get 1:100,000 [10mcg/ml]
- Infusion of 0.1mcg/kg/min–1mcg/kg/min, titrating from lower dose
- Dilute 6ml of 1:1000 [6mg] in 1L NS [6mcg/ml] start @ 1ml/kg/hr [0.1mcg/kg/min]
- If fluid an issue use 100ml NS [10mcg/ml] & start @ 0.1ml/kg/hr [0.1mcg/kg/min]
- If resistant to adrenaline (e.g. on –blockers), try 1–2mg glucagon IV over 5min
- IVC & Fluids:
- 0.9% Saline or colloid 500ml–1L [child 10–20ml/kg] boluses.
- Other therapies:
- Salbutamol 5mg [2.5mg<20kg] if bronchospasm only.
- Steroids (?may ↓delayed/biphasic reactions) if asthmatic or severe: hydrocortisone 200mg [child:4mg/kg] IV or prednisolone 50mg [1mg/kg] PO
- Antihistamines for skin manifestations. Avoid IV route as can ↓BP. H1±H2 blockers:
- Promethazine 10–25mg [child: 0.125–0.5mg/kg] PO or non-sedating **loratidine 10mg [child: 5mg if ≤6yr, 2.5mg if 1–2yr] PO
- Ranitidine 150mg [child: 3mg/kg] PO or 50mg [1mg/kg] IV
- Consider serial serum tryptase levels (immediately, 2hr & 24hr post-exposure) – if high suggests degranulation by mast cells (low level doesn’t exclude anaphylaxis)
- Outpatient allergy testing
- Observation for at least 6hrs and admit if:
- Asthmatic component to their anaphylactic reaction
- Previous history of biphasic reactions
- Possibility of continuing absorption of allergen
- Poor access to emergency care
- Presentation in the evening or at night
- Severe reactions with slow onset caused by idiopathic anaphylaxis
- On discharge:
- Organise prescription & education on usage of an EpiPen® (adult 300μg 1:1000 adrenaline, child<20kg 150μg 1:2000 adrenaline)
- Encourage patient to wear a Medic alert bracelet/necklace endorsed by doctor.
- Consider 3 day course of antihistamines and oral steroids.