The reliability of the plethysmographic perfusion index for detecting fluid responsiveness in critically ill patients

Abstract

Background

The assessment of fluid responsiveness (FR) is critical during the initial management of acute circulatory failure (ACF). However, in resource-limited settings or emergency situations, advanced hemodynamic monitoring is often unavailable. The plethysmographic perfusion index (PPI), a non-invasive parameter derived from pulse oximetry, has been proposed as a surrogate marker for changes in cardiac output. The objective of this study was to evaluate the ability of the PPI to detect FR in critically ill patients with ACF during early resuscitation.

Methods

This was a prospective observational study conducted over seven months (February to September 2024) in a 10-bed intensive care unit. Adult patients with ACF requiring a 500-mL fluid bolus were enrolled. FR was assessed by transthoracic echocardiography, defined as a ≥ 15% increase in left ventricular outflow tract velocity-time integral (VTI). VTI and PPI values were obtained before and immediately after the completion of fluid administration. The diagnostic performance of changes in PPI (ΔPPI) was assessed using receiver operating characteristic (ROC) curve analysis and a gray zone approach.

Results

Fifty patients (29 males and 21 females) were included, with a median age of 65 years (interquartile range [IQR]: 57–77). Sepsis-related ACF accounted for 60% of cases. FR was observed in 33 patients (66%). The area under the ROC curve (AUC) for ΔPPI was 0.778 (95% CI: 0.638 to 0.883, P = 0.004). A ΔPPI threshold of 33% yielded 70% sensitivity and 82% specificity. The gray zone ranged from 0% to 88%, encompassing 30% of the cohort.

Conclusion

The PPI demonstrated moderate accuracy in detecting FR during early resuscitation of ACF. As a simple, non-invasive, and widely accessible tool, PPI holds promise for informing fluid management decisions in emergency and critical care settings. Further technological refinements may enhance its diagnostic performance and broaden its clinical applicability.

Trial registration Clinical Trials.gov Identifier: NCT06313671.