Plasma NGAL-Detected Kidney Injury Following Paediatric Spine Surgery: Role of Intraoperative Hypotension

Background Post-operative acute kidney injury (AKI) remains a major complication in paediatric surgery. Serum creatinine is an insensitive marker, that increases only after significant impairment. Neutrophil gelatinase-associated lipocalin (NGAL) has emerged as an early biomarker capable of detecting tubular injury before functional decline. This study aimed to determine the incidence of AKI and subclinical AKI in paediatric spine surgery using plasma NGAL levels and to evaluate the associations of intraoperative hypotension with kidney injury. Methods In this prospective single-center study, 66 children (mean age 15.2 ± 1.7 years) who underwent elective posterior spinal instrumentation were enrolled. Plasma NGAL was measured after induction (T1, baseline), and subsequently at 6 and 24 hours after induction (T2 and T3, respectively). AKI was defined by the KDIGO criteria. ROC analysis was used to determine NGAL cut-off values; patients with NGAL above the threshold but without KDIGO-AKI were classified as having subclinical AKI. Risk factors, particularly intraoperative hypotension, were analyzed. Results Clinical AKI occurred in 12% of patients. The NGAL-T2 cut-off for AKI was 86 ng/mL (AUC = 0.817; sensitivity = 100%; specificity = 63.8%). Twenty-nine patients exceeded this threshold; 8 developed AKI and 21 (31.8%) had subclinical AKI. Intraoperative hypotension was the only independent predictor of kidney injury. Duration of MAP < 65 and < 70 mmHg were significantly longer in the AKI and subclinical AKI groups than in the non-AKI group. MAP < 60 mmHg was significantly prolonged only in the AKI group compared with both the subclinical AKI and non-AKI groups. Conclusions Although 12% of the children developed clinical AKI, one-third had subclinical AKI detectable only by NGAL. The plasma NGAL at the 6th hour showed excellent sensitivity for predicting AKI, with a threshold of 86 ng/mL. Intraoperative hypotension was a major predictor, with a MAP < 70 mmHg linked to tubular damage and a MAP < 60 mmHg associated with functional clinical AKI. This study is the first to define NGAL cut-off values and MAP thresholds for postoperative AKI in paediatric non-cardiac surgery.