Postoperative adverse events may be associated with substantial morbidity and mortality. However, inconsistent definitions of complications and unexpected events have limited accurate analysis of surgical outcomes. In 2004, the Clavien-Dindo classification for postoperative complications has been introduced and has since then been validated in numerous studies, with more than 20.000 citations.

Despite the appraisal of the Clavien-Dindo classification in the pediatric surgical literature, some criticize the transfer of grading systems for adults into a pediatric cohort without modification or validation. In a recent study we have shown that few items of the classification do not offer relevant information in pediatric cohorts and we have added organizational and management errors, not integrated in the initial proposal by Dindo et al. Especially, the variety of options for the management of complications based on institutional protocols and logistics is emphasized and a more focused and detailed assessment of the invasiveness of procedures in children is introduced.

Inclusion Criteria:

• All patients with unexpected events within the study period, treated at the department of pediatric surgery (preterms - 17 years of age), Hannover Medical School

Exclusion Criteria:

• None;

Data on all patients (preterm infants to 18 years of age) who experienced unexpected events at the Department of Pediatric Surgery Hannover Medical School from 1st January 2017 to 31st December 2021 were documented prospectively.