Introduction. Dynamic tests for predicting fluid responsiveness have generated increased interest in recent years. One of these tests, pulse pressure variation (PPV), is a parameter calculated from respiratory variations of pulse pressure. Another test, pleth variability index (PVI), is based on respiratory variations of the perfusion index and can be measured non-invasively by pulse oximeter. Previous studies have shown that both tests are valuable in determining fluid responsiveness.
Methods. In this observational prospective study, our aim was to compare the PVI and PPV in order to identify a convenient tool for determining fluid responsiveness. Our study was performed in a surgical and reanimation intensive care unit. We enrolled one hundred mechanically ventilated adult patients diagnosed with sepsis. Exclusion criteria included brain death, spontaneous breathing, cardiac arrhythmia, and impaired peripheral circulation. We measured the PPV by arterial monitorization and the PVI by using Masimo Radical 7 in the 45° semi-recumbent position (SP) and then 15° Trendelenbug position (TP). We performed correlation and ROC analysis using a >13% fluid responsiveness cut-off value for the PPV and >14% for the PVI.
Results. Between the SP and the TP, we did not observe significant decreases in PPV (from 14.17 ± 10.57 to 12.66 ± 9.64; p > 0.05), while we did observe significant decreases in PVI (from 21.91 ± 13.99 to 20.46 ± 14.12; p < 0.05). The PPV fluid responsiveness cut-off value in the SP and TP was 20% (78.95% sensitivity, 77.05% specificity) and 18% (76.67% sensitivity, 72.46% specificity), respectively. The PVI fluid responsiveness cut-off value in the SP and TP was 20% (80.49% sensitivity, 81.03% specificity) and 16% (81.25% sensitivity, 62.69% specificity), respectively. The area under the ROC of the PPV and PVI was 0.843 and 0.858 in the SP, respectively, and 0.760 and 0.747 in the TP, respectively. The PPV and PVI were correlated in the SP (r = 0.578; p = 0.001) and the TP (r = 0.517; p = 0.001).
Conclusions. Our results showed that the PPV and PVI were correlated independent of position change in sepsis patients. Both tests appear to be equivalently reliable. However, the ability of the PPV and PVI to predict fluid responsiveness decreased in the TP in our study.
Key words: pulse pressure variation, pleth variability index, fluid responsiveness, sepsis