Overview
Definition:
Anaphylaxis is a severe, potentially life-threatening, systemic allergic reaction characterized by rapid onset and progressive symptoms, mediated by mast cells and basophils releasing histamine and other mediators
In pediatrics, it represents a critical emergency requiring prompt recognition and management.
Epidemiology:
The incidence of anaphylaxis is increasing globally, with food allergies being the most common trigger in children, followed by insect stings and medications
Estimates vary, but pediatric anaphylaxis occurs frequently enough to be a significant concern for all healthcare providers dealing with children.
Clinical Significance:
Anaphylaxis is a medical emergency that can lead to cardiovascular collapse, airway obstruction, and death if not treated immediately
Understanding pediatric-specific nuances in presentation, epinephrine dosing, and the possibility of biphasic reactions is crucial for successful outcomes and exam success for DNB and NEET SS candidates.
Clinical Presentation
Symptoms:
Rapid onset of symptoms within minutes to hours of exposure to an allergen
Common symptoms include urticaria, angioedema, pruritus, flushing
Respiratory symptoms may include rhinorrhea, stridor, wheezing, dyspnea, cough, chest tightness
Gastrointestinal symptoms can include nausea, vomiting, abdominal pain, diarrhea
Cardiovascular symptoms can manifest as hypotension, syncope, dizziness, thready pulse
Neurological symptoms may include anxiety, restlessness, confusion, sense of impending doom.
Signs:
Vital sign abnormalities are common: tachycardia, tachypnea, hypotension, hypoxia
Physical examination may reveal diffuse urticaria, angioedema (especially of lips, tongue, larynx), laryngeal edema leading to stridor, bronchospasm causing wheezing, signs of shock (cool, clammy skin, weak pulse, altered mental status).
Diagnostic Criteria:
Diagnosis is primarily clinical, based on the rapid onset of symptoms involving skin/mucosal tissue, plus at least one of the following: respiratory compromise, reduced blood pressure or associated symptoms of hypoperfusion, or persistent gastrointestinal symptoms
A definitive diagnosis is made when exposure to a likely allergen occurs
The National Institute of Allergy and Infectious Diseases (NIAID) and the Food Allergy and Anaphylaxis Network (FAAN) criteria are widely used.
Diagnostic Approach
History Taking:
Crucial to obtain a detailed history of recent exposures (foods, medications, insect stings), temporal relationship between exposure and symptom onset, previous allergic reactions, personal or family history of atopy, asthma, or anaphylaxis
Identify potential triggers and any co-factors like exercise or concurrent medications.
Physical Examination:
A rapid, systematic assessment focusing on airway patency, breathing (respiratory rate, effort, auscultation for wheezing/stridor), circulation (heart rate, blood pressure, perfusion), and skin/mucosal findings (urticaria, angioedema)
Assess neurological status.
Investigations:
While diagnosis is clinical, laboratory investigations can support the diagnosis retrospectively
Serum tryptase levels (drawn 1-2 hours after symptom onset) can be elevated in anaphylaxis, but normal levels do not rule it out
Specific IgE testing or skin prick tests can identify causative allergens but are not useful during an acute episode.
Differential Diagnosis:
Differential diagnoses include asthma exacerbation, vasovagal syncope, psychogenic reactions, foreign body aspiration, viral croup, allergic rhinitis with conjunctivitis, food intolerance, and other causes of shock
The rapid, multi-system involvement distinguishes anaphylaxis.
Management
Initial Management:
Immediate recognition and cessation of exposure to the suspected allergen
If the patient is symptomatic, administer intramuscular epinephrine without delay
Place the patient in a supine position with legs elevated if hypotensive and no respiratory compromise
Maintain airway and administer oxygen if needed.
Medical Management:
The cornerstone of anaphylaxis management is intramuscular (IM) epinephrine
Dosage in pediatrics is weight-based: 0.01 mg/kg per dose, with a maximum of 0.3 mg per dose for children <30 kg and 0.5 mg for children >30 kg or those >12 years
Administer in the anterolateral thigh
Repeat doses may be given every 5-15 minutes if symptoms persist or worsen
Adjunctive therapies include antihistamines (H1 and H2 blockers) and corticosteroids, which are second-line agents and do not replace epinephrine
In severe bronchospasm, inhaled beta-agonists may be considered.
Surgical Management:
Not applicable for anaphylaxis itself, but airway management might involve procedures like intubation if severe laryngeal edema or bronchospasm compromises ventilation, performed by appropriately trained personnel.
Supportive Care:
Continuous cardiorespiratory monitoring is essential
Intravenous fluid resuscitation may be required for hypotension refractory to epinephrine
Patients should be observed for at least 4-6 hours after symptom resolution due to the risk of biphasic reactions
Education on allergen avoidance and provision of an epinephrine auto-injector prescription are critical.
Biphasic Reactions
Definition:
A biphasic reaction is the recurrence of anaphylactic symptoms without re-exposure to the inciting allergen, typically occurring 1-72 hours after the initial episode has seemingly resolved
This phenomenon is common in anaphylaxis and can be just as severe as the initial reaction.
Risk Factors:
Factors associated with an increased risk of biphasic reactions include severe initial anaphylaxis, delayed administration of epinephrine, concurrent use of beta-blockers, and certain triggers like insect stings
However, biphasic reactions can occur even in mild initial presentations.
Management And Observation:
Due to the risk of biphasic reactions, patients who have experienced anaphylaxis should be observed in a healthcare setting for a minimum of 4-6 hours after symptom resolution, and sometimes longer for severe cases
Those at high risk may require a longer observation period
Education on recognizing early signs of recurrence and prompt re-administration of epinephrine is vital
A prescription for an epinephrine auto-injector is mandatory for all patients discharged after an anaphylactic event.
Prevention Strategies:
Strict allergen avoidance remains the primary preventive strategy
Patients should be educated on reading food labels, avoiding known triggers, and carrying their epinephrine auto-injector at all times
Understanding the possibility of biphasic reactions and seeking immediate medical attention if symptoms recur is also crucial.
Key Points
Exam Focus:
High-yield facts for DNB/NEET SS include weight-based IM epinephrine dosing (0.01 mg/kg, max 0.3mg <30kg, 0.5mg >30kg), the route of administration (anterolateral thigh), recognition of biphasic reactions, and the recommended observation period
Understanding anaphylaxis as a clinical diagnosis and differentiating it from other conditions is also critical.
Clinical Pearls:
Always administer IM epinephrine first in suspected anaphylaxis
do not delay to establish IV access
Consider IM epinephrine for any child with acute onset of respiratory distress or cardiovascular compromise in the context of potential allergen exposure
Educate caregivers on proper auto-injector use and the importance of rapid re-administration if symptoms return.
Common Mistakes:
Common mistakes include underestimating the severity of anaphylaxis, delaying epinephrine administration, inadequate dosing of epinephrine, relying solely on antihistamines or corticosteroids as initial treatment, and insufficient observation periods leading to recurrence of symptoms due to biphasic reactions
Not prescribing an epinephrine auto-injector for discharge is a significant error.