Validity of Perfusion Index as a Predictor of Fluid Responsiveness by Echocardiography in Hypotensive Patients in Intensive Care

Background: Fluid responsiveness assessment is crucial in managing hypotensive critically ill patients. While transthoracic echocardiography (TTE) is widely used, the perfusion index (PI) offers a simple, non-invasive alternative. Objectives: To evaluate the validity of the perfusion index as a predictor of fluid responsiveness compared to echocardiographic assessment. Methods: This prospective observational study included 55 spontaneously breathing hypotensive ICU patients in the early period of ICU admission who received a 500 mL crystalloid fluid challenge. Stroke volume changes were assessed via velocity time integral (VTI) using transthoracic echocardiography. PI was recorded before and after fluid administration, and the percentage change in PI (ΔPI) was calculated. Results: Of 55 patients, 40 (72.7%) were responders and 15 (27.3%) non-responders. Baseline PI was not significantly different between groups (2.84 ± 1.50 vs. 2.31 ± 0.98; p = 0.21). After fluid administration, PI significantly increased in responders (3.99 ± 1.76) compared to non-responders (2.48 ± 1.04; p = 0.003). ΔPI was significantly higher in responders (54.06%) than non-responders (8.57%) (p = 0.001). ROC analysis showed ΔPI effectively discriminates between responders and non-responders with an AUC of 0.9183. The optimal cutoff of 13.79% yielded 85% sensitivity and 86.7% specificity. Conclusion: ΔPI% is a reliable, non-invasive predictor of fluid responsiveness in spontaneously breathing hypotensive ICU patients early in ICU admission, with strong correlation to changes in VTI and agreement with echocardiographic assessment.