190 Chapter 8 patients was stored in Castor EDC [13]. The patient reports were read by a dedicated PhD-candidate (LES), in case of doubt a paediatric surgeon (JD) was consulted. Data extraction The occurrence of SBO was based on the surgical report describing adhesions as the cause for obstruction without any other causes for obstruction (e.g., intestinal stenosis). Time from the primary surgery until SBO development was noted as was total followup duration, the diagnostic used for SBO diagnosis and (non-)surgical reinterventions. An anomaly was deemed congenital following the WHO definition (stating “all diseases that occurred during intrauterine life”) or as acquired after birth [14]. The primary operation was defined as the major operation for the first disease that occurred in an infant (e.g., pull-through in Hirschsprung’s disease (HD)). No procedures were excluded. Operative reports were searched to determine: operative approach (a conversion was quantified as laparotomy), age at primary surgery, if the primary surgery was an emergency procedure, if an anastomosis was created or if intestine was resected during primary surgery, the duration of surgery in hours, if the patient had a history of prematurity (gestational age <37 weeks) or a history of stoma formation/reversal, if an infection occurred following primary surgery and how many abdominal procedures were performed in total. If an operation was executed unscheduled and within 72 hours following admissions, it was seen as an emergency. Wound infection and wound dehiscence were combined into superficial infections, anastomotic leakage and intra-abdominal abscess were combined into deep infections and central line infections were grouped separately. Infectious complications were based on patient files as well as radiology reports. Line infections were noted only if they reported a positive blood culture and the patient reported fever above 38°C without another mentioned focus. Total number of abdominal procedures were categorized (1, 2, 3 or more) and were corrected for redo surgery for SBO. If specific data was missing within a patient this was indicated as “missing”. Statistical analysis Descriptive characteristics were reported as median with range in case of non-normally distributed variables or mean ± standard deviation (SD) in normally distributed variables. Since the first SBO occurred at eight days following primary surgery a minimum followup of at least 8 days was followed for the inclusion into the incidence analysis of SBO. One-way ANOVA was used to analyse if SBO incidence differed over the years comparing patients operated within a consecutive four-year period starting from 1998. Multivariate Cox regression was performed on the outcome of SBO. The proportional hazard assumption was graphically checked by log-minus-log plot for every included variable. Forward Wald selection was used for selection of variables and assessment of confounding (increase in B-coefficient of >10%) and effect modification (significant interaction term).
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