Pediatric Anaphylaxis

Anaphylaxis is highly likely when any 1 of the following 3 criteria are fulfilled:

The review presents the definition of anaphylaxis provided by the National Institute of Allergy and Infectious Disease and the Food Allergy and Anaphylaxis Network.

1. Acute onset of an illness (minutes to several hours) with involvement of the skin, mucosal tissue, or both (eg, generalized hives, pruritus or flushing, swollen lips-tongue-uvula) AND at least 1 of the following:

• Respiratory compromise (eg, dyspnea, wheeze-bronchospasm, stridor, reduced PEF, hypoxemia)
• Reduced BP or associated symptoms of end-organ dysfunction (eg, hypotonia [collapse], syncope, incontinence)

2. Two or more of the following that occur rapidly after exposure to a likely allergen for that patient (minutes to several hours):

• Involvement of the skin-mucosal tissue (eg, generalized hives, itch-flush, swollen lips-tongue-uvula)
• Respiratory compromise (eg, dyspnea, wheeze-bronchospasm, stridor, reduced PEF, hypoxemia)
• Reduced BP or associated symptoms (eg, hypotonia [collapse], syncope, incontinence); persistent gastrointestinal symptoms (eg, crampy abdominal pain, vomiting)

3. Reduced BP after exposure to known allergen for that patient (minutes to several hours):

• Infants and children: low systolic BP (age specific) or greater than 30% decrease in systolic BP
• Adults: systolic BP of less than 90 mm Hg or greater than 30% decrease from that person’s baseline

Based on this definition a patient can have anaphylaxis without any urticaria or mucosal signs. Furthermore, in the patient with known allergies, anaphylaxis may present as isolated hypotension.

Anaphylaxis tends to be under-diagnosed in emergency departments.

Unlike adults, food is the most common trigger of anaphylaxis in children, especially peanuts and tree nuts. Other foods include shellfish, fish, milk, eggs, soy and sesame. Medications and arthropod stings are the other important triggers.

Multiple studies have found an association between delay in adrenaline administration and death. However, death can still occur even when adrenaline is immediately administered.

Delay in adrenaline adminstration is also associated with increased rates of biphasic reactions. IM adrenaline administered to the lateral thigh is absorbed faster than SC adrenaline, though this has not been confirmed in patients experiencing anaphylaxis.

IM adrenaline is underused — both prehospital and in the emergency department. Don’t wait for hypotension to ensue!

Lab tests are not usually required.

The diagnosis of anaphylaxis is made clinically, and immediate treatment is necessary. Serum markers may be helpful for longterm management when the diagnosis of anaphylaxis is unclear.

Histamine levels

• peak within 10 minutes of onset of anaphylaxis
• return to baseline within 60 minutes.

Total tryptase levels

• may be tested within 3 hours of symptom onset.
• peak tryptase level correlated with severity of symptoms.
• normal tryptase levels do not rule out a diagnosis of anaphylaxis, and are more likely with food-related anaphylaxis

Biphasic reactions refer to the recurrence of anaphylaxis symptoms soon after the initial episode.

• occur about 5% of the time
• may occur >24 hours after the initial episode
• usually less severe than the initial episode
• possible risk factors include:
  1. delayed administration of adrenaline
  2. slow response to adrenaline
  3. need for repeated doses of adrenaline
  4. need for IV fluids

The dose of IM adrenaline for anaphylaxis is:

adrenaline 1:1000 (1 mg/mL) 0.01 mg/kg to a maximum of 0.3-0.5 mg IM

(i.e. 0.01 mL/kg of 1:1000 adrenaline)

This can be repeated every 3-5 minutes if life-threatening symptoms of hypotension, respiratory distress or stridor persist.

Don’t forget to give normal saline 10-20mL/kg boluses for persistent hypotension, and salbutamol nebulisers may help with ongoing bronchospasm. Patients on beta-blockers who do not respond to adrenaline may benefit from glucagon IV (20 to 30 mcg/kg up to a maximum of 1mg).

IV adrenaline may be given if there is no resolution despite multiple doses of IM adrenaline — experts vary in their recommendations of how to give this. APLS guidelines suggest 0.1-5.0 micrograms/kg/min, I prefer this simple approach:

• grab 1 mg of adrenaline 1:10,000 from the resus trolley
• inject into 1000mL bag of normal saline
• start infusion at 1 mL/min, which is 1 microgram/min
  (this would be 0.1 micrograms/kg/min for a 10 kg child)
• increase rate until resolution of severe anaphylaxis

Know your adrenaline doses!

Overdose can cause life-threatening tachyarryhthmias or even Tako-tsubo cardiomyopathy.

There is no evidence supporting the use of antihistamines in established anaphylaxis.

There may be some benefit in reducing cutaneous manifestations, based on a study showing the superiority of combined H1 and H2 blockers over H1 blockers alone in the treatment of mild allergic reactions. Avoid first-generation antihistamines like promethazine that are more likely to contribute to hypotension.

Prednisolone is often given to prevent the risk of a biphasic reaction. There is essentially no good evidence to support this practice. There is no evidence to guide dosing or duration.

APLS advises:

• hydrocortisone 4 mg/kg IV or IM then 2-4mg q6h

6 hours (in most cases; according to expert consensus guidelines)

However, admission should be considered for higher risk situations:

• severe anaphylaxis
• uncontrolled asthma
• slow response to adrenaline
• need for bolus fluids
• need for a second dose of adrenaline

Prior to discharge:

• provide appropriate discharge instructions (e.g. written action plan)
• teach use of adrenaline auto-injector
• provide prescriptions and ensure that the patient is able to fill them
• ensure that the patient can access to emergency medical services (e.g. phone, not too remote)
• arrange follow up

Most physicians do not know how to use an auto-injector…! Education is vital — in most cases of fatal anaphylaxis, an auto-injector is used incorrectly or not at all.