How to Diagnose Intra-operative Anaphylaxis

CLEVELAND CLINIC FOUNDATION

How to Recognise Intra-operative Anaphylaxis

Intraoperative allergic reactions are rare (every 5000 - 25000 anesthetics) but have a significant (3.4%) mortality rate.

More than 90% of allergic reactions evoked by intravenous drugs occur within 3 minutes. Muscle relaxants are commonly responsible. Latex reactions usually occur 20 - 60 minutes after induction, when transmucosal absorption of sufficient antigen has occurred.

Allergic reactions present a spectrum ranging from minor clinical changes to acute cardiovascular collapse leading to death. Severe reactions are known as anaphylactic and are recognised by a combination of respiratory, cardiovascular and cutaneous symptoms.

1. Respiratory

Laryngeal edema - presenting with stridor
Bronchospasm - presenting with wheezing, increased airway pressure
Pulmonary edema - presenting with auscultatory crackles, hypoxemia, decreased pulmonary compliance

2. Cardiovascular

Hypotension
Tachycardia
Decreased systemic vascular resistance
Pulmonary hypertension

3. Cutaneous

1. Urticaria and flushing

2. Angioedema affecting the tongue and oropharynx

3. Periorbital and perioral edema

NOTES:

When not all the cardinal features are present, anaphylaxis may mimic other diagnoses, such as:

Pulmonary embolism

Acute myocardial infarction

Aspiration

Vasovagal reaction

In the anesthetized patient, the most common manifestation is circulatory collapse, reflecting peripheral vasodilation and capillary leak, with resulting decreased venous return. In some patients, the only manifestation may be refractory hypotension.

Reactions may be protracted (>24 hrs) despite vigorous therapy.

During general anesthesia, patients may have altered sympathoadrenergic response to acute anaphylactic shock e.g. less tachycardia in response to hypotension.

During spinal or epidural anesthesia patients are sympathectomised, requiring earlier intervention with larger doses of epinephrine

Blood Tests

Serum mast cell tryptase levels are high during an episode and up to 4 hours after.

Complement C3 and C4 done at 30 mins, 1 and 4 hrs post-episode will show a serial increase.

Histamine levels increase acutely, then decrease rapidly

IgE levels will increase

Take two tubes of blood, one in an EDTA tube and one clotted specimen. These tests will help confirm the diagnosis of anaphylaxis, but do not identify latex as the antigen. Results will not be immediately available.