Background:Perfusion index (PI) is a noninvasive measure of perfusion. ΔPI (difference between pre- A nd postductal PI) may identify hemodynamically significant PDA. However, studies are limited to brief and intermittent ΔPI sampling. Our objective is to assess the value of continuous high resolution ΔPI monitoring in the diagnosis of PDA.Methods:Continuous ΔPI monitoring in preterm infants was prospectively performed using two high-resolution pulse oximeters. Perfusion Index measures (ΔPI mean and variability, pre- A nd postductal PI) were analyzed over a 4-h period prior to echocardiography. A cardiologist blinded to the results evaluated for PDA on echocardiography. Linear mixed regression models were utilized for analyses.Results:We obtained 31 echocardiography observations. Mean ΔPI (-0.23 vs. 0.16; P < 0.05), mean pre-PI (0.86 vs. 1.26; P < 0.05), and ΔPI variability (0.39 vs. 0.61; P = 0.05) were lower in infants with PDA compared to infants without PDA at the time of echocardiography.Conclusion:Mean ΔPI, ΔPI variability, and mean pre-PI measured 4 h prior to echocardiography detect PDA in preterm infants. PI is dynamic and should be assessed continuously. Perfusion index is a promising bedside measurement to identify PDA in preterm infants.