Background:Although the surgical outcomes of free flap reconstruction have improved over time,vascular compromise remains a devastating complication.Near-infrared spectroscopy(NIRS)is a promising new free flap monitoring technique with the potential for better outcomes than clinical monitoring(CM).This systematic re-view aims to provide a comprehensive review of the current evidence regarding the use of NIRS for free flap monitoring.Methods:A systematic literature review was performed,according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines,on existing NRIS studies,including the clinical outcomes of NIRS moni-toring,speed of detection,diagnostic accuracy,variables affecting NIRS accuracy,and cost-effectiveness.Results:A total of 24 articles were included in this analysis.In most instances of flap compromise,NIRS enabled earlier detection of compromise than did CM,by an average of 8.1(0.5-32.0)h.The flap salvage rate of flaps monitored with CM and NIRS(87.2%)was significantly higher than that of flaps monitored with CM alone(50.0%)(P<0.01).The overall survival rate for flaps monitored with CM and NIRS(98.1%)was also significantly higher than that for flaps monitored with CM alone(96.3%)(P=0.02).Blood oxygen saturation was the only variable with a significant effect on NIRS results.Conclusion:NIRS is an objective and reliable flap monitoring technique that provides superior flap salvage and survival rates compared with CM,which translates to cost savings and a reduction in workload for healthcare staff.Further large-scale studies are needed to standardize flap compromise criterion values and efficacy for different flap types.