Can anaphylaxis occur without hypotension?

Anaphylaxis Can Occur Without Hypotension

Yes, anaphylaxis can definitely occur without hypotension. According to diagnostic criteria from multiple guidelines, hypotension is not required for the diagnosis of anaphylaxis 1.

Diagnostic Criteria for Anaphylaxis

The presence of any ONE of these three criteria indicates anaphylaxis:

1. Acute onset involving skin/mucosal tissue PLUS at least one of:

   • Respiratory compromise (dyspnea, wheeze, stridor, hypoxemia)
   • Reduced blood pressure or associated end-organ dysfunction

2. Two or more of the following occurring rapidly after exposure to a likely allergen:

   • Skin/mucosal involvement (hives, itching, flushing, swollen lips/tongue)
   • Respiratory compromise
   • Reduced blood pressure or associated symptoms
   • Persistent gastrointestinal symptoms (cramping, vomiting)

3. Reduced blood pressure after exposure to a known allergen

Presentation Without Hypotension

Anaphylaxis commonly presents without hypotension for several reasons:

• In approximately 10% of cases, hypotension is the sole clinical feature, meaning 90% have other manifestations 1
• Cutaneous signs (urticaria, angioedema, flushing) occur in over 90% of cases, though their absence doesn't rule out anaphylaxis 1
• Respiratory symptoms such as bronchospasm, stridor, or dyspnea can be the predominant feature, especially in patients with pre-existing asthma 1

Epidemiology of Non-Hypotensive Anaphylaxis

• A population-based study found that only about 10% of anaphylaxis cases had hypotension and shock requiring urgent treatment 2
• Skin features may be absent in up to 20% of people with anaphylaxis 3
• Food-induced anaphylaxis, particularly in children, often presents with respiratory symptoms rather than cardiovascular collapse 3

Differential Diagnosis

When evaluating possible anaphylaxis without hypotension, consider:

• Vasovagal reactions: Distinguished by bradycardia (vs. tachycardia in anaphylaxis), absence of urticaria, and absence of bronchospasm 1
• Panic attacks: No significant vital sign changes 1
• Asthma exacerbation: Isolated respiratory symptoms without cutaneous manifestations
• Flushing syndromes: Related to medications, alcohol, or conditions like carcinoid 1

Clinical Pearls

• Anaphylaxis must be considered as a differential diagnosis for any acute-onset respiratory distress or bronchospasm, even without hypotension 3
• The absence of cutaneous symptoms speaks against anaphylaxis but does not rule it out 1
• Severe episodes characterized by rapid cardiovascular collapse can occur without cutaneous manifestations 1
• Methylene blue has been proposed as a treatment option for refractory anaphylaxis even in normotensive patients 4

Management Considerations

Even in the absence of hypotension, anaphylaxis treatment should follow standard protocols:

1. Administer intramuscular epinephrine in the lateral thigh as first-line treatment 1, 5
2. Position patient appropriately (supine if tolerated)
3. Provide supplemental oxygen if needed
4. Consider IV fluids even without hypotension if other signs of anaphylaxis are present
5. Monitor for biphasic reactions, which can occur hours after the initial reaction 1

Remember that anaphylaxis is a clinical diagnosis based on pattern recognition, and the absence of hypotension should not delay appropriate treatment when other diagnostic criteria are met.