Overview
Definition:
Food allergy is an adverse immune system reaction to specific food proteins
Anaphylaxis is a severe, potentially life-threatening systemic allergic reaction that can occur rapidly after exposure to an allergen
It is characterized by airway compromise, circulatory collapse, or both.
Epidemiology:
Food allergies affect approximately 5-8% of children under 3 years and 2-3% of adults
The most common culprits in children are milk, eggs, peanuts, soy, wheat, tree nuts, fish, and shellfish
Anaphylaxis is a significant cause of emergency department visits and hospitalizations, with estimates of 0.25% to 2% of anaphylaxis cases being fatal.
Clinical Significance:
Accurate diagnosis, prompt recognition of anaphylaxis, and effective management are crucial for preventing severe morbidity and mortality
Implementing a personalized anaphylaxis action plan and ensuring access to epinephrine autoinjectors are cornerstone strategies in pediatric practice for children with food allergies
This is a high-yield topic for DNB and NEET SS examinations.
Clinical Presentation
Symptoms:
Sudden onset of symptoms after food ingestion
Symptoms can include: Urticaria, angioedema, pruritus
Wheezing, stridor, dyspnea, cough
Nausea, vomiting, abdominal pain, diarrhea
Dizziness, syncope, feeling of impending doom
Rhinorrhea, sneezing.
Signs:
Vital sign abnormalities: Hypotension, tachycardia, hypoxia
Respiratory distress: Tachypnea, accessory muscle use, diffuse wheezing, stridor
Skin findings: Generalized urticaria, angioedema (especially of lips, tongue, face)
Cardiovascular collapse: Weak pulse, cyanosis
Neurological: Altered mental status, confusion, lethargy.
Diagnostic Criteria:
Diagnosis of anaphylaxis is primarily clinical, based on the abrupt onset of symptoms involving skin, mucosal, respiratory, cardiovascular, or gastrointestinal systems
Specifically, the National Institute of Allergy and Infectious Diseases (NIAID) and the Food Allergy and Anaphylaxis Network (FAAN) criteria are widely used: 1
Acute onset of illness involving skin, mucosal, or both (e.g., generalized hives, itching or flushing, swelling of lips-tongue-uvula)
AND / OR 2
Acute onset of hypotension/shock (e.g., fainting, collapse, limpness)
WITH respiratory compromise (e.g., dyspnea, bronchospasm, stridor, reduced peak expiratory flow, hypoxemia)
OR 3
Two or more of the following that occur rapidly after exposure to a likely allergen for that individual: skin/mucosal involvement
respiratory compromise
reduced blood pressure or visceral symptoms
persistent gastrointestinal symptoms (e.g., cramping, vomiting, diarrhea)
OR 4
Reduction in blood pressure after exposure to a known allergen for that individual (e.g., hypotension or collapse in infants and children, systolic blood pressure <70 mm Hg in children, <90 mm Hg in adults).
Diagnostic Approach
History Taking:
Detailed history of the suspected food trigger: timing of ingestion, amount consumed, onset and progression of symptoms
Previous allergic reactions to other foods or environmental allergens
Family history of atopy, asthma, or food allergies
Use of any medications prior to or during the reaction
Red flags: rapid onset, severe respiratory distress, hypotension, signs of shock.
Physical Examination:
Immediate assessment of Airway, Breathing, and Circulation (ABC)
Assess for stridor, wheezing, tachypnea, accessory muscle use
Palpate for pulses, assess for hypotension, pallor, or cyanosis
Examine skin for urticaria, angioedema, flushing
Assess for abdominal distension, tenderness, or signs of gastrointestinal distress.
Investigations:
While diagnosis is primarily clinical, investigations can support the diagnosis of food allergy in general
Serum tryptase: Elevated levels may support anaphylaxis, especially when drawn within 1-2 hours of symptom onset, but normal levels do not rule it out
Specific IgE testing (RAST/ELISA): Can identify sensitization to specific food allergens, but a positive test alone does not confirm allergy
Skin prick testing (SPT): Highly sensitive for IgE-mediated food allergy
Oral food challenges: Considered the gold standard for diagnosing food allergy but are performed under strict medical supervision
Note: These investigations are for diagnosing food allergy, not typically for confirming anaphylaxis in the acute setting.
Differential Diagnosis:
Other causes of acute onset symptoms: Vasovagal syncope
Acute asthma exacerbation
Scombroid poisoning (histamine fish poisoning)
Other food poisonings
Vocal cord dysfunction
Anxiety/panic attack
Laryngeal edema from other causes.
Management
Initial Management:
IMMEDIATE ADMINISTRATION OF EPINEPHRINE is the most critical first step in suspected anaphylaxis
Call for emergency medical services (EMS)
Place the patient in a supine position with legs elevated if hypotensive
upright position if experiencing respiratory distress
Administer oxygen if available and patient is hypoxic
Secure airway if necessary
Provide intravenous fluids for hypotension
Monitor vital signs continuously.
Medical Management:
Epinephrine: Intramuscular (IM) injection is the preferred route for first-line treatment
Dosage: For children <25 kg, 0.15 mg (1:1000 concentration)
For children >= 25 kg and adults, 0.3 mg (1:1000 concentration)
Administer into the anterolateral aspect of the thigh
May repeat every 5-15 minutes if symptoms persist or recur
Antihistamines: H1-receptor antagonists (e.g., diphenhydramine 1 mg/kg, max 50 mg in children
25-50 mg in adults) can help with cutaneous symptoms (hives, itching) but do not treat life-threatening airway or cardiovascular symptoms
H2-receptor antagonists (e.g., ranitidine, cimetidine) may provide additive benefit for urticaria
Corticosteroids: (e.g., methylprednisolone 1-2 mg/kg, max 125 mg in children
40-80 mg in adults) may help prevent prolonged or biphasic reactions and are typically given intravenously, but do not provide immediate benefit
Bronchodilators: Inhaled beta-agonists (e.g., albuterol) for bronchospasm
Glucagon: May be considered for refractory hypotension in patients on beta-blockers.
Surgical Management:
Not applicable for anaphylaxis itself, but emergency cricothyroidotomy or tracheostomy may be required in rare instances of irreversible airway obstruction refractory to medical management.
Supportive Care:
Continuous cardiorespiratory monitoring
Close observation in an emergency department or hospital setting for at least 4-6 hours (or longer depending on severity and response to treatment) due to risk of biphasic reactions
Patient and caregiver education regarding allergen avoidance, recognition of symptoms, and proper use of epinephrine autoinjectors
Provision of a written anaphylaxis action plan
Referral to an allergist for further evaluation and management.
Anaphylaxis Plan And Epinephrine Autoinjectors
Anaphylaxis Action Plan:
A personalized, written plan developed with a healthcare provider
It should clearly outline: the child's known allergens
The signs and symptoms of a reaction
Step-by-step instructions on what to do, including when and how to administer epinephrine
Instructions for calling emergency medical services
Emergency contact information
A copy should be carried by the child or caregiver at all times.
Epinephrine Autoinjector Use:
Epinephrine autoinjectors (e.g., EpiPen, EpiPen Jr, Auvi-Q) are pre-measured devices for easy IM administration
Education is paramount: 1
Select the correct device (e.g., Jr for <25 kg)
2
Remove safety cap
3
Hold firmly, with the blue end (retractable needle cover) pointing down
4
Swing and push firmly into the outer mid-thigh until a click is heard
5
Hold in place for the prescribed duration (usually 3-10 seconds)
6
Remove the autoinjector and massage the injection site for 10 seconds
7
Note the time of injection
8
Seek immediate medical attention.
Storage And Disposal:
Store autoinjectors at room temperature, away from extreme heat or cold, and protected from light
Regularly check expiration dates and replace as needed
Dispose of used autoinjectors promptly in a sharps container
follow local guidelines for disposal of medical waste.
Training And Practice:
Regular training and practice with trainer devices are essential for caregivers and older children to ensure confident and correct use during an emergency
Emphasize that it is better to use epinephrine if in doubt than to delay treatment.
Complications
Early Complications:
Cardiovascular collapse (anaphylactic shock)
Airway obstruction (laryngeal edema, bronchospasm)
Hypoxia
Death.
Late Complications:
Biphasic reactions (recurrence of symptoms hours later without re-exposure)
Prolonged symptoms
Psychological distress (anxiety, fear).
Prevention Strategies:
Strict allergen avoidance
Comprehensive education on food labels and cross-contamination
Maintaining an up-to-date anaphylaxis action plan
Ensuring immediate access to epinephrine autoinjectors
Regular follow-up with an allergist.
Prognosis
Factors Affecting Prognosis:
Promptness of epinephrine administration is the single most important factor
Severity of initial reaction
Presence of comorbidities (e.g., asthma)
Access to emergency medical care
Adequacy of allergen avoidance.
Outcomes:
With prompt and appropriate treatment, most patients with anaphylaxis recover fully without sequelae
However, delayed treatment or severe reactions can lead to significant morbidity and mortality
For children with food allergies, prognosis depends on adherence to avoidance strategies and preparedness for emergencies.
Follow Up:
Children diagnosed with food allergies should have regular follow-up with an allergist to monitor for resolution of allergies (some resolve with age, e.g., milk, egg), development of new allergies, and to review and update their anaphylaxis action plan and epinephrine prescription
Education reinforcement is crucial at each visit.
Key Points
Exam Focus:
Epinephrine is the first-line treatment for anaphylaxis
its administration should not be delayed
Understand the indications and proper administration of epinephrine autoinjectors
Recognize the clinical criteria for diagnosing anaphylaxis
Differentiate anaphylaxis from other conditions
Importance of a written anaphylaxis action plan.
Clinical Pearls:
Always carry two epinephrine autoinjectors
"When in doubt, use it." Teach at least two people how to administer epinephrine
Review expiration dates regularly
Encourage patients to wear medical identification (e.g., bracelet)
Remember that accidental ingestion of even small amounts of allergen can trigger a reaction.
Common Mistakes:
Delaying epinephrine administration
Treating anaphylaxis solely with antihistamines or corticosteroids
Inadequate patient and caregiver education on allergen avoidance and epinephrine use
Not having a written action plan or not carrying epinephrine
Assuming a previous mild reaction means future reactions will also be mild.