Predictive value of allergy tests for neuromuscular blocking agents: tackling an unmet need

Diagnostic procedure after an immediate hypersensitivity reaction in the operating room

The diagnosis of a perioperative allergic reaction is based on clinical features associated with a suggestive timeline, the exclusion of other diagnoses, elevated concentrations of degranulation markers (histamine, tryptase), and positive allergy assessments (skin tests, specific IgE). After initiating appropriate treatment, the anesthesiologist should take blood samples to measure histamine and tryptase concentrations just after the reaction and repeat them 1-2hours later to validate the diagnosis of immediate hypersensitivity. A delayed measurement of basal tryptase is useful to rule out mastocytosis and to interpret moderate tryptase levels. The anesthesiologist must inform the patient of the reaction to obtain adhesion and consent to subsequent investigations and must record the timing of the reaction and of the blood sampling, the possible causal agents, and the treatment administered. These data must be shared with the laboratory and the allergist. An adverse drug reaction report must be filed. The gold standard for allergy assessment is skin testing. These tests should be done in an appropriate facility, with experienced staff and in compliance with current guidelines. Specific IgE assays and cellular assays can help when clinical features and skin tests are discordant. Provocation tests are sometimes required. After allergy assessment, the safest protocol for subsequent anesthesia is determined in collaboration with the anesthesiologist. The patient must be informed and carry an allergy alert card.

[Allergy to neuromuscular blocking agents]

Allergy to neuromuscular blocking agents (NMBAs) has been the first cause of perioperative anaphylaxis for decades, in most countries. The most frequently involved agents are suxamethonium and rocuronium. The allergy work-up is compulsory to demonstrate or rule out allergy to NMBAs, if there is a compatible clinical history. Doing otherwise exposes the patient to death if the same or related NMBA is re-injected. In cases of true allergy, assessing cross-reactivity to other NMBAs is mandatory. The cross-sensitization hypothesis is presently being investigated and if confirmed, it could allow primary prevention measures to be implemented.

Perioperative anaphylaxis: what should be known?

Perioperative anaphylaxis is a unique condition as a result of the additive cardiovascular effects of anesthetics on the cardiovascular disturbances of anaphylaxis. It occurs mainly in adulthood, primarily follows anesthetic induction, and for the most part, is an IgE-mediated pathomechanism. Neuromuscular blocking agents (NMBAs) and antibiotics are the main culprit drugs, while latex is now infrequently involved. The Ring and Messmer scale is a useful tool for demonstrating the clinical severity of perioperative immediate hypersensitivity and guiding its management. Grades III and IV are life-threatening and are referred to as anaphylaxis. Three different clinical patterns of grade III may be observed, where cardiovascular collapse is the cardinal sign. Grade IV presents as cardiac arrest. The initial diagnosis is presumptive, whereas the etiological assessment is linked to the clinical presentation, tryptase levels, and skin test results. Since anaphylaxis presents with significant hypovolemia and vasoplegia, aggressive fluid therapy and epinephrine are the cornerstones of management. Whenever possible, anesthetic discontinuation is also recommended. Scientific evidence in favor of preemptive therapeutic strategies to prevent anaphylaxis in the operative setting is lacking.

Flowcytometric diagnosis of atracurium-induced anaphylaxis

BACKGROUND

Allergy to atracurium is a rare condition with serious consequences of diagnostic error. However, correct diagnosis is not always straightforward. The aim of this study is to assess the utility of the basophil activation test (BAT) in atracurium sensitization and to investigate its role in identifying cross-reactivity between muscle relaxants.

METHODS

For validation, eight patients with perioperative anaphylaxis to atracurium and seven individuals experiencing perioperative anaphylaxis but not exposed to neuromuscular blocking agents (NMBA) were included. Furthermore, five other patient groups were included in the study, and all individuals exposed to different NMBA, either sensitized or not to the drug. Basophil activation with atracurium was analysed flow cytometrically.

RESULTS

ROC analyses between eight atracurium-sensitized patients and seven nonexposed controls allowed identification of 5% as the decision threshold for BAT positivity. For this cutoff, the BAT attained a sensitivity of 63%, specificity of 100%, positive predictive value of 100% and negative predictive value of 70%. Of the atracurium-exposed individuals with a negative atracurium skin test (ST), two individuals had a clear positive BAT. BAT atracurium was positive in one cisatracurium-sensitized patient and negative in all cisatracurium-exposed patients with a negative ST to cisatracurium. All rocuronium- and suxamethonium-sensitized patients displayed a negative BAT with atracurium.

CONCLUSIONS

The BAT proves to be a useful diagnostic for atracurium-induced anaphylaxis and may be complementary to STs. The technique enables quick and simultaneous testing of potentially crossreactive NMBA and the identification of safe alternatives for future surgery.