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Anaphylaxis Workup and Allergy Assessment
TEXTPreop Eval · 9 min read
True IgE anaphylaxis is rare; mislabeled patients are common. Sorting them out before surgery prevents both crisis and over-restriction.
After this lesson you can
4 min read8 sections- Differentiate true allergy from intolerance.
- Plan for documented allergies.
- Recognize cross-reactivity patterns.
- Manage acute intraoperative reaction.
Allergy vs intolerance vs side effect
- rapid onset (minutes)
- at least two organ systems — typically urticaria + bronchospasm + hypotension + GI symptoms
- repeatable on re-exposure
- tryptase rises
- requires epinephrine
- GI upset
- headache
- mild flushing without true allergic features — uncomfortable
- not dangerous
Side effect / pharmacologic reaction: predictable drug effect at therapeutic dose (morphine pruritus from non-IgE mast-cell histamine release, vancomycin red-man from rate-related histamine release).
Document precisely — 'penicillin: hives at age 5' is very different from 'penicillin: ICU admission, intubated'.
PCN-allergy labels are inaccurate in ~90% of patients when systematically tested.
NMBA anaphylaxis — most common intraop trigger
Rocuronium dominant in modern series; succinylcholine and atracurium also implicated.
Cross-reactivity between NMBAs ~70% due to shared quaternary ammonium epitope.
Pholcodine (cough syrup ingredient, banned in several countries 2022) implicated in NMBA sensitization.
After rocuronium anaphylaxis: skin-prick + intradermal testing 4-6 weeks post-event to identify safe alternatives; sugammadex paradoxically does NOT improve anaphylaxis (binds rocuronium but mediator release already triggered).
Document with red wristband, chart flag, MedicAlert bracelet recommendation.
Penicillin-cefazolin cross-reactivity — modern numbers
True cross-reactivity is ~1-2% in modern formulations (the cited 10% number came from contaminated 1960s cephalosporins with PCN impurities).
Cefazolin side chain differs structurally from penicillin very low real cross-reactivity.
Avoid cefazolin only with documented severe IgE-mediated PCN history: anaphylaxis, Stevens-Johnson syndrome, toxic epidermal necrolysis, drug-induced hemolytic anemia, DRESS, serum sickness.
Mild PCN reactions (rash, GI upset, no anaphylaxis) cefazolin is safe with standard observation.
Don't substitute clindamycin or vancomycin reflexively — they have higher SSI rates than cefazolin in clean cases.
Chlorhexidine, latex, antibiotics, dyes
- anaphylaxis incidence rising — sensitization from CHG-impregnated catheters
- surgical prep
- mouthwash
- wound dressings
Often presents 10-20 min after prep + drape rather than at induction (delayed because intact skin slows absorption).
Becoming a top-3 intraop trigger.
Latex: declining in healthcare (latex-free standard since ~2010) but persists in older facilities.
- spina bifida (multiple early-life surgeries)
- healthcare workers
- patients with multiple atopic reactions
- first case of day
- all latex-free supplies
- communicate to whole team
- vancomycin (true IgE rare, red-man common)
- clindamycin
- sulfa
Blue dyes (methylene blue, patent blue V for sentinel node) — anaphylaxis up to 1% with patent blue.
Recognizing intraop anaphylaxis
- unexplained hypotension refractory to fluid + small-dose pressor
- rising peak airway pressures
- drop in ETCO2 (from bronchospasm + cardiac output drop)
- flushing visible above drape
- urticaria on uncovered skin
- pulmonary embolism
- hemorrhage
- septic shock
- vagal response
- drug overdose
Treat empirically while sorting it out — epinephrine bolus is therapeutic AND diagnostic (rapid response supports anaphylaxis).
Tryptase for diagnosis
1-2 hr post-event, returns to baseline by 24 hr.Diagnostic threshold: acute level >11.4 ng/mL OR an acute:baseline ratio formula of (1.2 × baseline) + 2. Total tryptase alone is less specific.
- time of event (or as close as possible)
1-2 hrpost (peak)- 24+ hr (baseline) — three timepoints
Baseline ≥20 ng/mL flags possible mastocytosis (clonal mast-cell disease, prone to spontaneous anaphylaxis).
Refer all confirmed intraop anaphylaxis to allergy 4-6 weeks post-event for specific IgE + skin testing.
Preop allergy interview technique
- hospitalization
- intubation
- epinephrine use
- oxygen
- ICU — markers of severity
Specifically ask about NMBA exposure history (prior anesthetics), antibiotics, chlorhexidine, latex.
Document drug + reaction + timing + management.
Update the EHR problem list with VERIFIED vs reported reactions.
PCN-allergy de-labeling programs (oral challenge or skin testing) free patients from suboptimal abx — refer to allergy clinic if uncertain.
Don't propagate inaccurate labels forward.
Treatment protocol — epinephrine first
- stop trigger
- 100% O₂
- IV fluids wide open
EPINEPHRINE is first-line — adult bolus 10-100 mcg IV titrated, infusion 0.05-0.2 mcg/kg/min for ongoing.
IM 0.3-0.5 mg if no IV.
- H1 blocker (diphenhydramine 25-50 mg IV)
- H2 blocker (famotidine 20 mg IV)
- steroid (hydrocortisone 200 mg IV or methylpred 1-2 mg/kg)
Beta-2 agonist (albuterol) for bronchospasm.
Glucagon 1-5 mg IV if patient on beta-blocker (epinephrine refractory).
Vasopressin 1-2 U IV if refractory hypotension.
Biphasic reaction occurs in 5-20% — observe in monitored setting ≥6 hr (longer if reaction severe).
⚠ Common pitfalls
- Treating any GI upset as antibiotic allergy — most patients with 'penicillin allergy' tolerate cephalosporins.
- Forgetting latex allergy assessment — relevant in spina bifida + healthcare workers.
- Avoiding all NMBs in 'NMB allergy' — specific drug matters; cross-reactivity testing helpful.
- Treating intra-op reaction as 'just histamine' when it's anaphylaxis.
💎 Clinical pearls
- Penicillin allergy + need for cephalosporin: 1-2% cross-reactivity for 1st-gen; lower for later generations.
- Rocuronium has higher anaphylaxis incidence than cisatracurium.
- Latex precautions: scheduled first case of the day, latex-free OR.
- Allergy testing referral post-event with tryptase + skin testing 6 weeks later.
Recap
- Penicillin allergy + need for cephalosporin: 1-2% cross-reactivity for 1st-gen; lower for later generations.
- Rocuronium has higher anaphylaxis incidence than cisatracurium.
- Latex precautions: scheduled first case of the day, latex-free OR.
- Allergy testing referral post-event with tryptase + skin testing 6 weeks later.
Mark each section done to complete the module.