Objective:To analyze the changes of peripheral perfusion index (PPI) with late-onset sepsis (LOS) in very low birth weight infants during hospitalization.Methods:Very low birth weight infants admitted to the neonatal intensive care unit of Children′s Hospital of Fudan University from August 1, 2021 to August 31, 2022 were consecutively included.Infants with admission age ≥three days and unstable circulation, or positive blood culture within three days after birth were excluded.From the day of admission, the PPI values of the right hand and either foot of the infants were measured with Masimo SET Radical-7 everyday while whether LOS occurred during hospitalization was observed.The mean PPI curve of very and extremely low birth weight infants without LOS was plotted.For those with LOS confirmed by blood culture, the PPI change trajectory three days before and after the occurrence of LOS was drawn, and the change trend of PPI before the occurrence of LOS was analyzed by trend chi-square test.Non-parametric test was used to analyze the effect of LOS on pre- and post-ductal PPI values.Results:A total of 107 very low birth weight infants were included in the final analysis.Among them, there were 11 infants confirmed as LOS by blood culture, 37 infants diagnosed as clinical LOS, and 59 infants without LOS.Pre-and post-ductal PPI values of very low birth weight infants without LOS were 2.06±1.30 and 1.72±0.92, respectively; those with clinical LOS were 1.90±0.94 and 1.58±0.83, respectively; those with LOS confirmed by blood culture were 1.92±1.11 and 1.62±0.82, respectively.For infants with LOS confirmed by blood culture, the pre-and post-ductal PPI values showed a continuous downward trend during three days before the onset of disease, with the lowest PPI values on the first day before the diagnosis of blood culture.The downtrend of pre-ductal PPI was statistically significant ( χtrend2=5.57, P<0.05). Conclusion:The PPI value of very low birth weight infants show a downward trend when LOS occurs.It should be observed dynamically in clinical practice, which is helpful to suspect or identify LOS as early as possible.