Postoperative morbidity after suspected grade III perioperative immediate hypersensitivity reactions with completed surgery: a matched case-control study.

BACKGROUND: Severe immediate perioperative hypersensitivity reactions (POH) are uncommon but potentially life-threatening events. Postoperative morbidity after suspected grade III POH when surgery is completed remains uncertain. This study compared postoperative morbidity between patients with suspected grade III POH whose surgery was completed and matched controls. METHODS: We conducted a retrospective, single-centre, matched case-control study at Lille University Hospital between 2012 and 2023. Cases were adults with suspected grade III POH, defined by a Hypersensitivity Clinical Scoring Scheme (HCSS) score ≥11, whose surgery was completed after haemodynamic stabilisation. Controls without POH were matched for age, sex, surgical procedure, body mass index, ASA physical status, and surgical period. Thirty-day postoperative morbidity and mortality were assessed by medical record review. Associations were analysed using conditional logistic regression. RESULTS: Thirty-five cases were matched with 101 controls. The composite outcome occurred in 25.7% of cases and 10.9% of controls (odds ratio 3.54; 95% confidence interval 1.14-11.00; p = 0.029). In patients with documented mast cell activation, the association was not statistically significant (odds ratio 1.57; 95% confidence interval 0.24-10.31; p = 0.64). DISCUSSION: Patients with suspected grade III POH whose surgery was completed had a higher incidence of postoperative morbidity than matched controls undergoing similar surgical procedures. The association was not statistically significant in patients with documented mast cell activation, but the estimate was imprecise. These findings provide additional outcome data relevant to the 2025 French recommendations for the management of stabilised grade III POH. Multicentre studies are needed to confirm these findings and define their perioperative implications.