What are the signs and symptoms of a patient in anaphylactic shock?

Signs and Symptoms of Anaphylactic Shock

As an EMT, you should expect to see cutaneous manifestations (flushing, urticaria, angioedema, pruritus) in over 90% of anaphylactic patients, combined with respiratory distress (stridor, wheezing, dyspnea) and/or cardiovascular collapse (hypotension, tachycardia, syncope), though severe cases can present with shock alone without any skin findings. 1

Initial Presentation and Early Warning Signs

The initial symptoms are often nonspecific and include: 1

• Tachycardia (most common cardiac finding)
• Sensation of impending doom
• Faintness or lightheadedness
• Cutaneous flushing
• Agitation or anxiety

The patient may appear either flushed or pale, and diaphoresis is common. 1, 2

Cutaneous Manifestations (Present in >90% of Cases)

Urticaria is the most common physical finding in anaphylaxis. 1 Look for: 1, 3

• Diffuse or localized urticaria (hives)
• Angioedema (swelling of deeper tissues, particularly eyelids, lips, tongue)
• Diffuse erythema (redness)
• Pruritus (itching) - may be diffuse or localized

Critical Pitfall

The absence of cutaneous symptoms does NOT rule out anaphylaxis - severe episodes with rapid cardiovascular collapse can occur without any skin manifestations, particularly when hemodynamic collapse develops rapidly. 1, 3, 4 Up to 10% of anaphylactic reactions may lack cutaneous findings. 1

Respiratory System Involvement (40-60% of Cases)

Upper Airway Signs

• Rhinitis (common early sign of respiratory involvement) 1
• Hoarseness or voice changes (dysphonia) 1
• Sensation of throat tightness or foreign body in larynx 2
• Stridor (indicates severe laryngeal edema and impending airway obstruction) 1
• Oropharyngeal swelling 1
• Lingual edema (tongue swelling) 1

Lower Airway Signs

• Wheezing (from bronchospasm/asthma-like symptoms) 1
• Cough 1
• Shortness of breath/dyspnea 1, 5
• Decreased oxygen saturation 2

Respiratory compromise becomes more severe as upper airway edema progresses, and can rapidly lead to complete airway obstruction. 1

Cardiovascular System Involvement (30-35% of Cases)

Hemodynamic Changes

• Hypotension (systolic BP <90 mmHg) 1, 5
• Tachycardia (the rule in anaphylaxis) 1
• Thready or unobtainable pulse 6
• Syncope or near-syncope 1, 6
• Cardiovascular collapse/shock 1, 5

Important Exception

Bradycardia can occur during anaphylaxis due to the Bezold-Jarisch reflex (a cardioinhibitory reflex), particularly in patients with conduction defects, increased vagal tone, or those taking sympatholytic medications. 1, 3 This can mimic a vasovagal reaction, but the presence of urticaria, bronchospasm, and other allergic features distinguishes anaphylaxis. 1

Pathophysiology of Shock

Increased vascular permeability allows transfer of up to 50% of intravascular fluid into the extravascular space within 10 minutes, causing profound hypovolemia (up to 37% of circulating blood volume loss) and rapid hemodynamic collapse. 1, 4 This vasodilatory shock can develop with minimal or absent cutaneous/respiratory manifestations. 4

Gastrointestinal Symptoms (25-30% of Cases)

• Nausea 1, 5
• Vomiting 1, 6
• Diarrhea 1, 6
• Abdominal cramps 6

Neurological Manifestations

• Altered level of consciousness (may reflect hypoxia) 1
• Dizziness or weakness 1, 5
• Headache 1
• Sense of impending doom 1
• Unconsciousness 1
• Convulsions (in severe cases) 6

Other Findings

• Involuntary voiding (loss of bladder control) 6
• Uterine cramps (in women) 1
• Congestion and sneezing 5

Timing and Progression

The more rapidly anaphylaxis develops after exposure to the trigger, the more likely the reaction is severe and potentially life-threatening. 1, 4 Most reactions occur within minutes of exposure, though some may develop >30 minutes after exposure. 1

Biphasic Reactions

Late-phase or biphasic reactions can occur 8-12 hours after the initial attack, and protracted severe anaphylaxis may last up to 32 hours despite aggressive treatment. 1, 3 This necessitates extended observation periods, particularly for severe reactions. 7

Differential Diagnosis: Distinguishing from Vasovagal Reactions

Vasovagal (vasodepressor) reactions are the most commonly confused condition with anaphylaxis. 1 Key distinguishing features: 1

Feature	Anaphylaxis	Vasovagal Reaction
Urticaria	Usually present	Absent
Heart rate	Tachycardia (usually)	Bradycardia
Bronchospasm	May be present	Absent
Blood pressure	Hypotension	Normal or increased
Skin	Flushed, warm	Cool, pale

However, remember that bradycardia CAN occur in anaphylaxis, so this distinction is not absolute. 1

Clinical Assessment Algorithm

When evaluating a potential anaphylaxis patient, assess: 1

1. Level of consciousness (impairment suggests hypoxia)
2. Upper and lower airways (dysphonia, stridor, cough, wheezing, dyspnea)
3. Cardiovascular system (hypotension, syncope, cardiac arrhythmias)
4. Skin (erythema, pruritus, urticaria, angioedema)
5. Gastrointestinal system (nausea, vomiting, diarrhea)

Cardiovascular and respiratory status can change rapidly in anaphylactic shock, making continuous close monitoring imperative. 1