Passive leg raising test induced changes in plethysmographic variability index to assess fluid responsiveness in critically ill mechanically ventilated patients with acute circulatory failure

Background: Passive leg raising (PLR) reliably predicts fluid responsiveness but requires a real-time cardiac index (CI) measurement or the presence of an invasive arterial line to achieve this effect. The plethysmographic variability index (PVI), an automatic measurement of the respiratory variation of the perfusion index, is non-invasive and continuously displayed on the pulse oximeter device. We tested whether PLR-induced changes in PVI (Delta PVIPLR) could accurately predict fluid responsiveness in mechanically ventilated patients with acute circulatory failure.Methods: This was a secondary analysis of an observational prospective study. We included 29 mechanically ventilated patients with acute circulatory failure in this study. We measured PVI (Radical-7 device; Masimo Corp., Irvine, CA) and CI (Echocardiography) before and during a PLR test and before and after volume expansion of 500 mL of crystalloid solution. A volume expansion-induced increase in CI of >15% defined fluid responsiveness. To investigate whether Delta PVIPLR can predict fluid responsiveness, we determined areas under the receiver operating characteristic curves (AUROCs) and gray zones for Delta PVIPLR.Results: Of the 29 patients, 27 (93.1%) received norepinephrine. The median tidal volume was 7.0 [IQR: 6.6-7.6] mL/kg ideal body weight. Nineteen patients (65.5%) were classified as fluid responders (increase in CI > 15% after volume expansion). Relative Delta PVIPLR accurately predicted fluid responsiveness with an AUROC of 0.89 (95%CI: 0.72-0.98, p < 0.001). A decrease in PVI <= -24.1% induced by PLR detected fluid responsiveness with a sensitivity of 95% (95%CI: 74-100%) and a specificity of 80% (95%CI: 44-97%). Gray zone was acceptable, including 13.8% of patients. The correlations between the relative Delta PVIPLR and changes in CI induced by PLR and by volume expansion were significant (r = -0.58, p < 0.001, and r = -0.65, p < 0.001; respectively).Conclusions: In sedated and mechanically ventilated ICU patients with acute circulatory failure, PLR-induced changes in PVI accurately predict fluid responsiveness with an acceptable gray zone.