T78.0XXA anaphylactic reaction due to food initial encounter
T80.5XXA anaphylactic reaction due to serum initial encounter
T63.44XA toxic effect of bee venom initial encounter
T88.6XXA anaphylactic reaction due to adverse effect of correct drug initial encounter
SNOMED CT concepts
39579001 anaphylaxis
62315008 anaphylactic shock
Laboratory Tests
Core labs in moderate to severe presentations
Baseline and severity assessment
Point-of-care glucose for altered mental status
Hypoglycemia alternative cause of symptoms
Venous blood gas for severe respiratory distress
pH and pCO2 in mmHg
Lactate for shock or persistent hypotension
Trend with resuscitation
Electrolytes and renal function
Fluid resuscitation and vasopressor planning
Allergy mediator testing
Tryptase and related testing
Serum tryptase for suspected anaphylaxis with unclear trigger
Peak typically 1-2 hours after symptom onset
Declines toward baseline by about 6 hours
If available then baseline tryptase after recovery
Mast cell disorder screening
Pitfalls and limitations
Test interpretation cautions
Normal tryptase does not exclude anaphylaxis
More likely to rise in hypotension and venom reactions
Leukocytosis and stress hyperglycemia nonspecific
Do not anchor on infection without evidence
Diagnostic Tests
Scoring Systems
Diagnostic criteria and grading
NIAID FAAN clinical criteria framework
Acute skin mucosal involvement plus respiratory compromise
Acute skin mucosal involvement plus reduced blood pressure or end-organ dysfunction
After likely allergen exposure with two or more systems involved
Skin mucosal
Respiratory
Reduced blood pressure or end-organ dysfunction
Persistent gastrointestinal symptoms
After known allergen exposure with reduced blood pressure
Adults systolic blood pressure less than 90 mmHg or greater than 30 percent decrease from baseline
Children age-specific low systolic blood pressure or greater than 30 percent decrease
WAO anaphylaxis severity grading concepts
Mild
Skin mucosal symptoms only
Moderate
Respiratory symptoms without hypoxia
GI symptoms with significant distress
Severe
Hypoxia
Hypotension or collapse
Neurologic compromise
MRI
Limited role imaging considerations
MRI indications for alternative diagnosis
Neurologic deficits not explained by hypoperfusion
Suspected spinal pathology unrelated to allergic reaction
MRI contraindications and constraints
Unstable airway or hemodynamics
Delayed access and monitoring challenges
CT
Alternative diagnosis evaluation
CT indications when symptoms atypical
Severe abdominal pain with peritoneal signs
Suspected pulmonary embolism features
Suspected aortic pathology features
CT risks
Iodinated contrast reactions
Treat reactions as anaphylaxis if occur
Ultrasound
Point-of-care ultrasound adjuncts
Shock differentiation support
Cardiac function
Hyperdynamic ventricle in distributive physiology
IVC assessment
Collapsibility suggesting hypovolemia component
Lung ultrasound
B-lines for cardiogenic pulmonary edema alternative
Pleural effusion alternative
Disposition
Observation and admission criteria
Post-treatment risk stratification
Observation candidates
Complete symptom resolution after treatment
No hypotension episode
No airway edema progression
Admission indications
Recurrent symptoms requiring repeat epinephrine
Hypotension or shock
Persistent bronchospasm or hypoxia
Airway involvement
Tongue or laryngeal edema concern
Epinephrine infusion required
Observation duration and biphasic reaction risk
Monitoring time concepts
Minimum observation interval
At least 4-6 hours for resolved mild to moderate reactions
Extended observation or admission interval
At least 12-24 hours for severe reactions
Prior biphasic reaction history
Delayed epinephrine administration
Unknown trigger with ongoing risk
Transfer and consultation triggers
Escalation needs
ICU level care triggers
Epinephrine infusion
Persistent hypotension
Mechanical ventilation
Specialist follow-up needs
Allergy immunology referral
Mast cell disorder evaluation for recurrent idiopathic episodes
Treatment
First-line epinephrine and immediate therapies
Epinephrine first-line
Intramuscular dosing
Adults 0.3-0.5 mg IM of 1 mg/ml in anterolateral thigh
Repeat every 5-15 minutes if persistent symptoms
Pediatrics 0.01 mg/kg IM of 1 mg/ml in anterolateral thigh
Maximum single dose 0.5 mg
Repeat every 5-15 minutes if persistent symptoms
Auto-injector dosing
0.15 mg for smaller children per device labeling
Use when available and appropriate size
0.3 mg for older children and adults per device labeling
Use when available and appropriate size
Intravenous infusion for refractory symptoms
Indication
Persistent hypotension after IM epinephrine and fluids
Ongoing severe bronchospasm after IM epinephrine
Preparation safety
Dedicated infusion pump
Continuous cardiac monitoring
Starting dose range
0.05-0.1 microg/kg/min
Titrate every 2-5 minutes to perfusion targets
Alternative adult starting dose
1-4 microg/min
Titrate upward as needed
Airway and oxygenation support
Oxygen therapy
Nonrebreather for hypoxia
Escalate based on work of breathing
Nebulized bronchodilator
Salbutamol 2.5-5 mg nebulized
Repeat as needed for wheeze
Ipratropium 0.5 mg nebulized
Add for severe bronchospasm
Nebulized epinephrine for upper airway symptoms
Racemic epinephrine 2.25 percent 0.5 ml nebulized
Repeat as needed while preparing definitive airway
Fluids and vasopressors
Volume resuscitation
Isotonic crystalloid bolus
Adults 1-2 litres rapid infusion
Repeat based on blood pressure and perfusion
Pediatrics 20 ml/kg bolus
Repeat up to 60 ml/kg for shock with reassessment
Additional vasopressors when needed
If refractory to epinephrine infusion then adjunct vasopressor
Norepinephrine infusion per shock protocol
Titrate to mean arterial pressure target
Vasopressin adjunct
Consider in catecholamine-refractory shock
Adjunct medications
H1 antihistamine for cutaneous symptoms
Diphenhydramine 25-50 mg IV or IM
Sedation risk and delirium risk
Cetirizine 10 mg PO when able
Less sedation than first-generation agents
H2 blocker adjunct
Famotidine 20 mg IV or PO
Adjunct only
Corticosteroid adjunct
Methylprednisolone 125 mg IV
Consider for asthma comorbidity and prolonged symptoms
Prednisone 40-60 mg PO when able
Discharge taper individualized
Antiemetic adjunct
Ondansetron 4-8 mg IV or ODT
Supportive symptom control
Refractory anaphylaxis special situations
Beta-blocker associated refractory symptoms
Glucagon therapy
Adults 1-5 mg IV over 5 minutes
Follow with infusion 5-15 microg/min
Titrate to hemodynamic response
Pediatrics 20-30 microg/kg IV over 5 minutes
Maximum 1 mg
Follow with infusion 5-10 microg/min
Adverse effects
Vomiting risk
Aspiration precautions
Bradykinin-mediated angioedema overlap
If isolated angioedema without urticaria then consider bradykinin mechanism
Epinephrine still appropriate if airway compromise
Targeted therapies per angioedema protocol if confirmed
Evidence levels and guideline statements
Guideline aligned care concepts
Epinephrine as first-line therapy
Class I recommendation in major allergy society guidance
Antihistamines not effective for airway or shock
Adjunct only
Corticosteroids not reliable for biphasic prevention
Use as adjunct for comorbid asthma or prolonged symptoms
ACEP Level B or C alignment
Early epinephrine prioritized over adjunctive therapies
Special Populations
Pregnancy
Pregnancy considerations
Maternal stabilization priority
Maternal oxygenation and perfusion as fetal protection
Epinephrine use
Not contraindicated in anaphylaxis
Same IM dosing as nonpregnant adults
Positioning
Left uterine displacement in late pregnancy
Improve venous return
Obstetric consultation triggers
Persistent maternal hypotension
Uterine contractions or vaginal bleeding
Geriatric
Older adult considerations
Higher baseline cardiovascular risk
Monitor for ischemia during catecholamine therapy
Medication interactions
Beta-blocker and alpha-blocker use more common
Lower physiologic reserve
Lower threshold for admission after severe episode
Pediatrics
Pediatric considerations
Weight-based dosing emphasis
Epinephrine 0.01 mg/kg IM of 1 mg/ml
Fluid bolus 20 ml/kg isotonic crystalloid
Age-specific hypotension thresholds
Use pediatric shock references for low systolic blood pressure
Common triggers by age
Foods in younger children
Venom and medications in older children
Background
Epidemiology
Frequency and outcomes
Common triggers
Foods
Medications
Venom
Biphasic reaction concept
Recurrence after initial resolution
Higher risk with severe initial presentation
Fatality risk factors
Delayed epinephrine
Severe asthma
Cardiovascular disease
Pathophysiology
Mechanisms
Mast cell and basophil mediator release
Histamine
Leukotrienes
Prostaglandins
Resulting physiologic effects
Vasodilation and capillary leak
Bronchospasm
Mucosal edema
Phenotypes
IgE-mediated
Non-IgE mediated
Idiopathic
Therapeutic Considerations
Rationale for epinephrine
Alpha-1 effects
Vasoconstriction and reduced mucosal edema
Beta-1 effects
Increased cardiac output
Beta-2 effects
Bronchodilation
Reduced mediator release
Adjunct limitations
Antihistamines
Symptom relief for hives only
Corticosteroids
Delayed onset
Uncertain impact on biphasic reactions
Patient Discharge Instructions
copy discharge instructions
Discharge packet
Diagnosis
Anaphylaxis
Medications and devices
Epinephrine auto-injector prescribed
Carry at all times
Demonstration of correct use
Practice trainer when available
Second auto-injector recommended
Some reactions require repeat dosing
Avoidance plan
Identified trigger avoidance
Label reading and cross-contamination precautions for food allergy
Follow-up
Allergy immunology appointment
Primary care follow-up within 1 week
Return to emergency department immediately for
Any breathing difficulty
Throat tightness or voice change
Fainting or severe dizziness
Worsening swelling of lips or tongue
Recurrent hives with vomiting or abdominal pain
Need for epinephrine use
References
Clinical guidelines and evidence sources
Key sources
World Allergy Organization anaphylaxis guidance
Diagnostic criteria and management recommendations
AAAAI ACAAI practice parameters for anaphylaxis
Epinephrine as first-line therapy
NIAID FAAN anaphylaxis criteria publication
Clinical diagnostic framework
ACEP emergency care guidance concepts
Early epinephrine emphasis in ED pathways
SymptomDx is an educational tool for medical professionals. It does not replace clinical judgment. Verify all clinical data and drug dosages with authoritative sources.