Postoperative Acute Kidney Injury in Children Undergoing Major Non-cardiac Surgery

Incidence of postoperative AKI

Incidence of postoperative AKI, defined according to the Kidney Disease: Improving Global Outcomes (KDIGO) creatinine criteria, based on changes in plasma/serum creatinine concentration from baseline within the postoperative period: * AKI Stage 1: Increase in plasma/serum creatinine ≥ 0.3 mg/dL (26.5 µmol/L) within 48 hours postoperatively OR 1.5-1.9 times baseline plasma/serum creatinine within 7 postoperative days. * AKI Stage 2: Increase in plasma/serum creatinine 2-2.9 times baseline p/s creatinine within 7 postoperative days. * AKI Stage 3: Increase in plasma/serum creatinine \> 3 times baseline plasma/serum creatinine within 7 postoperative days OR increase in plasma/serum creatinine to 4.0mg/dL (353.6 µmol/L) OR Initiation of renal replacement therapy OR decrease in eGFR to \< 35mL/min per 1.73 m2. All within 7 postoperative days. Baseline creatinine is defined as a plasma/serum creatinine value obtained within 24 hours prior of commencement of surgery.

Agreement and association between changes in plasma/serum creatinine and urinary biomarkers of renal injury.

Examples of urinary biomarkers: Neutrophil gelatinase-associated lipocalin (NGAL) Kidney injury molecule-1 (KIM-1) Tissue inhibitor of metalloproteinase 2 (TIMP-2) Insulin-like growth factor binding protein-7 (IGFBP-7) S100 calcium-binding protein A8 (S100A8) Osteoprotegerin (OPG) Galectin 3 Elastase Cystatin C Albumin/Creatinine-ratio

Time from surgery to first AKI-qualifying creatinine

Perioperative risk factors associated with postoperative AKI

Diagnostic accuracy of plasma cystatin C for postoperative AKI and agreement with creatinine-based definitions.

These analyses aim to evaluate how well urinary biomarkers discriminate AKI versus no AKI within the postoperative window. Biomarker distributions will be assessed and skewed biomarkers will be log-transformed as appropriate. Defined rules for values below/above assay limits (LLOQ/ULOQ) will be applied (e.g., imputation at LLOQ/2 for below LLOQ, or use of censored methods if needed) based on approach specified per assay. If urine dilution adjustment is used (e.g., indexing to urine creatinine), both raw and indexed values will be examined and available in main text or in supplement. The primary diagnostic measure will be the area under the receiver operating characteristic curve (AUROC) with 95% CI (e.g., DeLong method). ROC curves will be presented for each biomarker. If clinically meaningful cut-offs are available, sensitivity, specificity, positive/negative predictive values, and likelihood ratios will be reported with 95% CIs. If no established cut-offs exist, an "optimal" cut-of

Incidence of postoperative dysnatraemia and associated risk factors

Incidence of postoperative dyschloremia and associated risk factors.

Incidence of postoperative dyskalemia and associated risk factors.

Incidence of postoperative AKI defined by urine output

Urine output criteria for AKI will be recorded where available, but creatinine-based KDIGO criteria constitute the primary diagnostic definition. If patient age at time of surgery ≥ 28 days: AKI Stage 1: \<0.5 mL/kg/h for 6-12h AKI Stage 2: \<0.5 mL/kg/h for ≥ 12h AKI Stage 3: \<0.3 mL/kg/h for ≥24h or anuria ≥12h If patient age at time of surgery \< 28 days: AKI Stage 1: \<1 mL/kg/h for ≥24h AKI Stage 2: \<0.5 mL/kg/h for ≥24h AKI Stage 3: \<0.3 mL/kg/h for ≥24h or anuria ≥12h