Pleth Variability Index or Inferior Vena Cava Collapsibility Index? Prospective Observational Study in Volume Control and Follow-Up Acute Kidney Injury

<i>Background and Objective</i>: Acute kidney injury (AKI) is a serious condition requiring prompt fluid resuscitation, yet both under- and over-treatment carry risks. Accurate volume assessment is essential, especially in emergency settings. The Inferior Vena Cava Collapsibility Index (IVCCI) is commonly used but has limitations. The Pleth Variability Index (PVI) offers a non-invasive alternative, though its role in AKI remains unclear. To compare the efficacy of the Pleth Variability Index (PVI) and Inferior Vena Cava Collapsibility Index (IVCCI) in assessing fluid responsiveness and predicting in-hospital mortality in patients with acute kidney injury. <i>Materials and Methods</i>: This prospective observational study enrolled 50 adult AKI patients presenting to a tertiary emergency department. All patients received sequential fluid resuscitation with 1000 mL and 2000 mL of isotonic saline. PVI, IVCCI, mean arterial pressure (MAP), peripheral oxygen saturation (SpO₂, perfusion index (PI), and shock index (SI) were recorded at baseline and after each fluid bolus. Changes in these parameters were analyzed to assess their utility in fluid responsiveness. Additionally, the prognostic value of baseline PVI for in-hospital mortality was investigated. <i>Results</i>: PVI demonstrated a significant and dose-responsive decrease following fluid administration, outperforming IVCCI, MAP, PI, SpO₂, and SI in sensitivity (<i>p</i> < 0.001). Baseline PVI values were significantly associated with mortality (AUC: 0.821, <i>p</i> < 0.001), whereas post-resuscitation PVI values showed no prognostic significance. IVCCI and PI showed comparable reliability but were less sensitive to incremental volume changes. <i>Conclusions</i>: PVI is a sensitive, non-invasive marker of fluid responsiveness in non-intubated AKI patients and may also serve as an early prognostic indicator. Its use in emergency departments could support fluid management decisions, but further large-scale, multicenter studies are needed to validate these findings.