Mechanism of Cardiac Arrest in Fatal Anaphylaxis

Anaphylaxis is a short duration, potentially catastrophic allergic reaction where a rapid return to a person's baseline can be expected if vital organ function can be supported. Fatal anaphylaxis is a rare but potentially preventable cause of death at all ages. The three main mechanisms of rapid organ system failure leading to cardiac arrest in anaphylaxis are upper airway obstruction, lower respiratory obstruction principally from bronchospasm and cardiovascular failure. We aimed to measure the frequency and timing of each organ failure type leading to fatal anaphylaxis to further inform treatment recommendations.

We performed a population-based retrospective cohort analysis for the period 1 January 2003 to 31 December 2022 using Australian clinical data contained within the National Coronial Information System. The primary outcome was the primary organ that failed leading to initial physiological decompensation. Secondary objectives were to compare the time course of deterioration and complications between allergen groups. Multivariate logistic regression was used to quantify adjusted odds ratios between allergen categories for each of the three organ failure types.

There were 371 anaphylaxis deaths for the study period (mean age 55.7 years, male 58.5%) with the primary outcome recorded in 250 (67.4%). In overall all-cause anaphylaxis fatalities, the most common organ failure was bronchospasm-induced respiratory failure (n = 153, 61.2%). Cardiovascular failure was less common (n = 73, 29.2%) and upper airway obstruction occurred in 24 (9.6%). There were significant differences in the primary organ system failure according to allergen trigger categories. Fatal food anaphylaxis was exclusively associated with respiratory failure (bronchospasm 94.8%, upper airway 5.2%).

We found that respiratory failure rather than cardiovascular failure was the most common cause of cardiorespiratory arrest in fatal anaphylaxis. Death from food-triggered anaphylaxis appears to be exclusively a primary respiratory event. International anaphylaxis guidelines require appropriate emphasis on respiratory symptoms and treatment to further reduce the risk of anaphylaxis fatalities.