Physical Examination Findings in Anaphylaxis
Anaphylaxis presents with a constellation of physical findings affecting multiple organ systems, most commonly including cutaneous manifestations (urticaria, angioedema), respiratory distress (bronchospasm, stridor), and cardiovascular compromise (hypotension, tachycardia). 1
Key Physical Examination Findings by System
Cutaneous Findings (71.9-93.7% of cases)
- Widespread flushing or erythema
- Urticaria (hives)
- Angioedema (swelling of lips, tongue, eyelids)
- Pruritus (itching)
- Important caveat: Cutaneous signs may be absent in up to 20% of cases, particularly in rapidly progressive anaphylaxis 1, 2
Respiratory Findings (39.8% of allergic anaphylaxis)
- Upper airway:
- Stridor
- Dysphonia (voice changes)
- Laryngeal edema
- Rhinitis (early sign)
- Lower airway:
- Wheezing
- Bronchospasm (more common in patients with pre-existing asthma)
- Tachypnea
- Respiratory distress
- Hypoxia
Cardiovascular Findings (74.7% of allergic anaphylaxis)
- Hypotension (may be the sole finding in ~10% of cases)
- Tachycardia (most common)
- Bradycardia (seen in approximately 10% of cases)
- Cardiovascular collapse (50.8% of allergic anaphylaxis)
- Cardiac arrest (5.9% of allergic anaphylaxis)
- Weak/thready pulse
- Syncope
Gastrointestinal Findings
- Nausea
- Vomiting
- Diarrhea
- Abdominal cramps
- Involuntary voiding
Neurological Findings
- Altered level of consciousness (may reflect hypoxia)
- Lightheadedness
- Headache
- Feeling of impending doom
- Unconsciousness
Timing of Physical Findings
- Most findings develop within minutes of exposure to the triggering agent
- Some reactions may be delayed up to 30-60 minutes after exposure
- Biphasic reactions can occur 8-12 hours after the initial attack
- Protracted anaphylaxis may last up to 32 hours despite treatment 1
Differential Diagnosis Considerations
The physical exam can help distinguish anaphylaxis from other conditions:
- Vasovagal reaction: Absence of urticaria, bradycardia (not tachycardia), absence of bronchospasm, normal or elevated blood pressure, cool and pale skin 1
- Panic attack: Normal vital signs, absence of objective cutaneous findings
- Asthma exacerbation: Absence of cutaneous and cardiovascular findings
- Cardiogenic shock: Absence of cutaneous and respiratory findings
Special Considerations
- Increased vascular permeability can lead to transfer of up to 50% of intravascular fluid into extravascular space within 10 minutes, resulting in rapid hemodynamic collapse 1
- Anaphylaxis must be considered as a differential diagnosis for any acute-onset respiratory distress, bronchospasm, hypotension, or cardiac arrest 2
- The more rapidly anaphylaxis occurs after exposure to the trigger, the more likely the reaction is to be severe and potentially life-threatening 1
Remember that anaphylaxis is primarily a clinical diagnosis based on physical examination findings across multiple organ systems. The absence of cutaneous findings does not rule out anaphylaxis, especially in rapidly progressive cases.