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Toronto Notes 2019 Medical Emergencies Medical Emergencies
Anaphylaxis and Allergic Reactions
Etiology
• anaphylaxisisanexaggeratedimmunemediatedhypersensitivityreactionthatleadstosystemic histamine release, increased vascular permeability, and vasodilation; regardless of the etiology, the presentation and management of anaphylactic reactions are the same
• allergic(re-exposuretoallergen)
• non-allergic(e.g.exerciseinduced)
Diagnostic Criteria
• anaphylaxisishighlylikelywithanyof:
1. acute onset of an illness (min to hrs) with involvement of the skin, mucosal tissue and at least one of
■ respiratory compromise (e.g. dyspnea, wheeze, stridor, hypoxemia)
■ hypotension/end-organ dysfunction (e.g. hypotonia, collapse, syncope, incontinence)
2. two or more of the following after exposure to a LIKELY allergen for that patient (min to hrs)
■ involvement of the skin-mucosal tissue
■ respiratory compromise
■ hypotension or associated symptoms
■ persistent gastrointestinal symptoms (e.g. crampy abdominal pain, vomiting)
3. hypotension after exposure to a KNOWN allergen for that patient (min to h)
■ management is also appropriate in cases which do not fulfill criteria, but who have had previous
episodes of anaphylaxis
■ life-threatening differentials for anaphylaxis include asthma and septic shock
■ angioedema may mimic anaphylaxis but tends not to improve with standard anaphylaxis treatment
Management
• moderatereaction:generalizedurticaria,angioedema,wheezing,tachycardia ■ epinephrine (1:1000) 0.3-0.5 mg (IM in anterolateral thigh)
■ antihistamines: diphenhydramine (Benadryl®) 25-50 mg PO/IV
■ salbutamol (Ventolin®) 1 cc via MDI
• severereaction/evolution:severewheezing,laryngeal/pulmonaryedema,shock
■ ABCs, may need definitive airway (e.g. ETT) due to airway edema
■ epinephrine (1:1000) 1-10 μg/min IV (or via ETT if no IV access) titrated to desired effect
■ antihistamines: diphenhydramine (Benadryl®) 50 mg IV (~1 mg/kg)
■ glucocorticoids: methylprednisolone 125-250 mg IV or prednisone/prednisolone 40-60 mg PO ■ large volumes of crystalloid may be required
Disposition
• monitorfor4-8hinED(minimum)andarrangefollow-upwithfamilyphysicianin24-48h • can have second phase (biphasic) reaction up to 72 h later, patient may need to be supervised • educatepatientonavoidanceofallergens
• medications
■ H1 antagonist (cetirizine 10 mg PO OD or Benadryl® 50 mg PO q4-6h x3d)
■ H2 antagonist (ranitidine 150 mg PO OD x3d)
■ corticosteroid (prednisone 50 mg PO OD x5d) to prevent secondary reaction
Asthma
• seeRespirology,R7
• chronicinflammatoryairwaydiseasewithepisodesofbronchospasmandinflammationresultingin
reversible airflow obstruction
History and Physical
• findcause(s)ofasthmaexacerbation(viral,environmental,etc.)
• historyofasthmacontrol;severityofexacerbations(ICU,intubationhistory) • signsofrespiratorydistress
• vitals,specificallyO2
Investigations
• peakflowmeter
• ±ABGifinsevererespiratorydistress
• CXRifdiagnosisindoubttoruleoutpneumonia,pneumothorax,etc.
Emergency Medicine ER29
Most Common Triggers for Anaphylaxis
• Foods (nuts, shellfish, etc.)
• Stings
• Drugs (penicillin, NSAIDs, ACEI) • Radiographic contrast media
• Blood products
• Latex
Anaphylaxis should be suspected if airway, breathing, or especially circulation compromise is present after exposure to a known allergen
Hypotension is defined as systolic BP >30% decrease from baseline or
• ≥11 yr: <90 mmHg
• 1-10yr:<70mmHg+(2xage)
• 1 mo-1 yr: <70 mmHg
Early epinephrine is lifesaving and there are no absolute contraindications
Pediatric Dosing
• Epinephrine: 0.01 mg/kg IM up to 0.5mg q5-10min
• Initial crystalloid bolus: 20-30 mL/kg, reassess
• Epinephrine infusion: 0.1-1.5 μg/kg/min • Diphenhydramine: 1 mg/kg PO/IV q4-6h • Ranitidine: 1 mg/kg PO/IV
• Methylprednisolone: 1-2 mg/kg IV
Beware of the silent chest in asthma exacerbations. This is a medical emergency and may require emergency intubation