Diagnostic accuracy of Plethysmographic Variability Index for the prediction of high pulse pressure variation in neurosurgery using a gray-zone approach: a retrospective study

BACKGROUND: Unlike pulse pressure variation (PPV), the Plethysmographic Variability Index (PVI) has shown limited and heterogenous reliability in predicting fluid responsiveness, especially during dynamic intraoperative periods.METHODS: This retrospective study assessed the accuracy of PVI in predicting high PPV (>13%) using high resolution vital records acquired during neurosurgery. In addition, a new set of cut-off values of PVI for predicting PPV >13% was derived using a gray-zone approach. This study included consecutive patients who underwent neurosurgery with both PPV and PVI monitoring in a single operating room. Vital data from each individual were aggregated after 1000 repeated random samplings to generate a pooled data set. The discriminative power of PVI was assessed using receiver operating characteristic (ROC) curves. A new set of cut-offs was derived, in which sensitivity or specificity was ≥0.90.RESULTS: A total of 730,000 seconds of data from 73 patients were analyzed. The Spearman correlation co-efficient between PPV and PVI in the pooled data set was 0.356 and repeated measures correlation was 0.199. The optimal cut-off of PVI for >13% PPV was 14.5, with a sensitivity of 0.67 and a specificity of 0.70 (area under the ROC curve [AUC] 0.739). The newly determined lower and upper cut-offs for the gray-zone approach were 9 and 21, respectively.CONCLUSIONS: A single cut-off value of PVI may not accurately predict fluid responsiveness. Using a gray-zone approach, PVI <9 or >21 can rule in or rule out high PPV and may be more useful in actual clinical practice.