Messina A, Montagnini C, Cammarota G, et al. - Researchers evaluated the sensitivity as well as the specificity of baseline pulse pressure variation (PPV) and stroke volume variation (SVV), the tidal volume (V_T) challenge (V_TC) and the end-expiratory occlusion test (EEOT) for the prediction of fluid responsiveness during elective spinal surgery. They initiated the study protocol during a period of intraoperative hemodynamic stability following prone positioning and prior to the delivery of any vasopressor. The protocol comprised of 8 steps and following each step, a complete set of hemodynamic measurements was documented. Post-V_TC use, the alteration in PPV enabled the prediction of fluid responsiveness with an area under the curve of 0.96, demonstrating sensitivity and specificity of 95.2% and 94.7%, respectively, utilizing a cutoff increase of 12.2%. With an area under the curve 0.96, fluid responsiveness was predicted by alteration in SVV following V_TC use, with sensitivity and specificity of 95.2% and 94.7%, respectively, using a cutoff increase of 8.0%. Overall, fluid responsiveness in prone elective neurosurgical patients was not predicted by the baseline values of PPV and SVV and the EEOT. Findings highlighted the extreme reliability of V_TC as a functional hemodynamic test which could be valuable in guiding intraoperative fluid therapy.