Anaphylaxis

Diagnosis:
Anaphylaxis is highly likely when ANY ONE of the following 2 criteria are fulfilled:
 

1. Acute onset of illness with mucocutaneous involvement and at least ONE of the following:

i. Respiratory symptoms:

• Wheezing, stridor, dyspnea, throat tightness.

ii. Hypotension:

• Systolic blood pressure <90 mmHg or a >30% drop from baseline.

iii. Gastrointestinal disturbances:

• Abdominal pain, vomiting, diarrhea.
  
   

2. Acute onset of hypotension or bronchospasm or laryngeal involvement after exposure to a known or highly probable allergen for that patient, even in the absence of typical skin involvement. 

Remember:

• Skin or mucosal changes alone are not sign of anaphylaxis.
• Skin and mucosal changes can be subtle or absent in 10-20% of reactions

 

1. Rapid Clinical Assessment & Stabilization

• ABCDE approach
• Positioning:
  • ​Put patient in semi recumbent or supine with or without leg elevation.
  • Avoid walking or standing during acute reactions.
  • Pregnant patients should lie on their left side to prevent aortocaval compression.
• High-Flow Oxygen (HFMO₂):
  • ​Administer at 15 L/min to maintain adequate oxygen saturation.
  • Nebulised adrenaline (5mL of 1:1000 adrenaline) can be used to treat partial upper airway obstruction, but should not be prioritised over adrenaline infusion or delay tracheal intubation in cases of critical upper airway obstruction.

 

 

2. Adrenaline (Epinephrine) Administration:

Give as soon as possible

Adult Dose:

Adrenaline 0.5 mL (0.5 mg) of 1:1000 solution IM injected into the mid-lateral thigh.

 

Repeat every 5 minutes if there is no improvement in the patient's condition.

 

Pediatric Dosing:

>12 years: 0.5 mg IM (0.5mL)

6 - 12 years: 0.3 mg IM (0.3mL)

6 months - 6 years: 0.15 mg IM (0.15mL)

< 6 months: 0.1 - 0.15 mg IM (0.1 to 0.15mL)

 

If no improvement in cardiorespiratory symptoms after 2 doses (refractory anaphylaxis), consider IV adrenaline infusion:

• 1 mg diluted in 100 mL of normal saline (NS)
• Run continuous infusion at 0.5 - 1 mL/kg/hour using an infusion pump.
• Titrate according to response.
  • Tachycardia, tremor, pallor with a normal or raised BP may indicate ecessive adrenaline treatment, reduce the infusion rate (or stop infusion if severe).
• Weaning:
  • As symptoms improve, reduce the infusion (aiming for 50% of the starting rate)
  • 1 hour after resolution of all symptoms and signs - reduced the infusion rate progressively over 30 min and then stop.

*Continue to repeat IM adrenaline every after 5 min until the infusion has been started.

 

3. Special Considerations:

Patients on Beta-Blockers they may not respond effectively to adrenaline.

Glucagon (1-5 mg over 5 minutes) IV

Followed by an infusion at 5-15 mcg/min if necessary.

 

 

4. Bronchodilator Therapy:

Administer MDI or nebulized salbutamol if bronchospasm is present.

 

Note: Be prepared for potential intubation if there is impending airway obstruction due to angioedema.

 

 

5. Supportive:

i. Fluid:

• Give rapid IV crystalloid bolus in the presence of shock, or poor response to an initial dose of adrenaline.

ii. Antihistamine:

• Not recommended as initial emergency treatment - no role in treating cardiorespiratory symptoms of anaphylaxis.
• Recommended in alleviating persistent cutaneous symptoms once patient has been stabilised.
• Use a non-sedating oral histamine (e.g. cetrizine) in preference to chlorphenamine.
• There is no evidence to support use of an H2-receptor antihistamine (e.g. ranitidine) to treat anaphylaxis.

iii. Corticosteroid:

• Routine use to treat anaphylaxis is not advised. (Resuscitation Council UK 2021)
• Primary action is the downregulation of the late-phase inflammatory response.
  • However, there is little evidence that it help shorten protracted symptoms or prevent biphasic reactions.
• May consider giving steroids after initial resuscitation in refractory reaction or ongoing asthma / shock.

 

 

6. Discharge and Follow-up 
Biphasic reaction can occurs in 5% of patients.

Risk factors for biphasic reaction following anaphylaxis include:

• More severe initial presentation of anaphylaxis

• Initial reaction requiring more than one dose of adrenaline.

• Delay in adrenaline administration ( >30 - 60 minutes from symptoms onset).

• Good response (within 5–10 minutes) to a single dose of adrenaline given within 30 minutes of onset of reaction 
• Complete resolution of symptoms 
• The patient already has unused adrenaline auto-injectors and has been trained how to use them 
• There is adequate supervision following discharge

• 2 doses of IM adrenaline needed to treat reaction 
• Previous biphasic reaction

• Severe reaction requiring >2 doses of adrenaline 
• Patient has severe asthma or reaction involved severe respiratory compromise 
• Possibility of continuing absorption of allergen, e.g. slow-release medicines 
• Patient presents late at night, or may not be able to respond to any deterioration 
• Patients in areas where access to emergency care is difficult

References:

1. American College of Allergy, Asthma, and Immunology. (2020). Anaphylaxis: Guidelines for emergency management.

2. Resuscitation Council UK. (2021). Emergency treatment of anaphylactic reactions: Guidelines for healthcare providers. Resuscitation Council UK.

3. Simons, F. E. R., Ardusso, L. R. F., Bilò, M. B., El-Gamal, Y. M., Ledford, D. K., Ring, J., ... & World Allergy Organization. (2011). World Allergy Organization anaphylaxis guidelines: Summary. The Journal of Allergy and Clinical Immunology, 127(3), 587–593. https://doi.org/10.1016/j.jaci.2010.11.020

4. Lieberman, P., Nicklas, R. A., Randolph, C., Oppenheimer, J., Bernstein, D., Bernstein, J., ... & Kemp, S. F. (2015). Anaphylaxis—a practice parameter update 2015. Annals of Allergy, Asthma & Immunology, 115(5), 341–384. https://doi.org/10.1016/j.anai.2015.07.019

5. Sheikh, A., Shehata, Y. A., Brown, S. G., & Simons, F. E. (2009). Adrenaline (epinephrine) for the treatment of anaphylaxis with and without shock. Cochrane Database of Systematic Reviews, (4). https://doi.org/10.1002/14651858.CD006312.pub2

6. Kemp, S. F., Lockey, R. F., Simons, F. E., & Epinephrine in Anaphylaxis Study Group. (2008). Epinephrine: The drug of choice for anaphylaxis. A statement of the World Allergy Organization. Allergy, 63(8), 1061–1070. https://doi.org/10.1111/j.1398-9995.2008.01733.x

7. Brown, S. G. A. (2004). Clinical features and severity grading of anaphylaxis. The Journal of Allergy and Clinical Immunology, 114(2), 371–376. https://doi.org/10.1016/j.jaci.2004.04.029