Validity of Pleth Variability Index to Predict Fluid Responsiveness in Patients Undergoing Cervical Spine Surgery in the Modified Prone Position

<i>Background and Objective</i>: The modified prone position, which is an alteration of the standard prone position, reduces cardiac preload. Dynamic variables including stroke volume variation (SVV), pulse pressure variation (PPV), and pleth variability index (PVI) are reliable predictors for fluid responsiveness during surgery. To the best of our knowledge, no studies assessing dynamic variables for fluid responsiveness have been conducted in the modified prone position. This study aimed to evaluate the ability of PVI to predict fluid responsiveness in the modified prone position during cervical spine surgery. <i>Materials and Methods:</i> PVI, SVV, and PPV were recorded at the following times: before and after a 4 mL/kg crystalloid load in the supine position (T1, T2); after placement in the modified prone position (T3); and before and after a 4 mL/kg crystalloid administration in the modified prone position (T4, T5). Fluid responsiveness was defined as stroke volume (SV) ≥ 15%, assessed by the FloTrac/Vigileo™ (Edwards Lifesciences Corp, Irvine, CA, USA). Receiver operating characteristic (ROC) curves were analyzed to identify changes in each dynamic variable that could predict fluid responsiveness in the modified prone position. <i>Results:</i> Data from a total of 43 subjects were analyzed. In the supine position, 21 subjects were responders. After subjects were placed in the modified prone position, SV significantly decreased, while PVI, SVV, and PPV significantly increased (<i>p</i> < 0.001 for all). In the modified prone position, 13 subjects were responders, and the areas under the ROC curves for ΔPVI, ΔSVV, and ΔPPV after fluid loading were 0.524 (95% confidence interval [CI] 0.329-0.730, <i>p</i> = 0.476), 0.749 (95% CI 0.566-0.931, <i>p</i> = 0.004), and 0.790 (95% CI 0.641-0.938, <i>p</i> < 0.001), respectively. <i>Conclusions:</i> Crystalloid pre-loading could not mitigate the decrease in SV caused by the modified prone position. Changes in PVI were less reliable in predicting fluid responsiveness in the modified prone position.