Tidal Volume Challenge to Assess Volume Responsiveness with Dynamic Preload Indices During Non-Cardiac Surgery: A Prospective Study

<b>Background/Objectives</b>: The aim of this study is to assess whether changes in Pulse Pressure Variation (PPV) and Stroke Volume Variation (SVV) following a VtC can predict the response to fluid administration in patients undergoing surgery under general anesthesia with protective mechanical ventilation. <b>Methods</b>: A total of 40 patients undergoing general surgery or vascular surgery without clamping the aorta were enrolled. Protective mechanical ventilation was applied, and the radial artery was catheterized in all patients. The protocol began one hour after the induction of general anesthesia and the stabilization of hemodynamic parameters. The parameters PPV₆ and SVV₆ were recorded during ventilation with a Vt of 6 mL/kg Ideal Body Weight (IBW) (T1). Then, the Vt was increased to 8 mL/kg IBW for 3 min without changing other respiratory parameters. After the VtC, the parameters PPV₈ and SVV₈ (T2) were recorded. After the stabilization of hemodynamic parameters, volume expansion (VE) was administered with colloid fluid of 6 mL/kg IBW. Parameters before (T3) and 5 min after fluid challenge (T4) were recorded. The change in the Stroke Volume Index (SVI) before and after VE was used to indicate fluid responsiveness. Patients were classified as fluid responders (SVI ≥ 10%) or non-responders (SVI < 10%). <b>Results</b>: The parameter ΔPPV(6-8) demonstrated good predictive ability to predict fluid responsiveness, evidenced by an Area Under the Curve (AUC) of 0.86 [95% Confidence Interval (CI) 0.74 to 0.95, <i>p</i> < 0.0001]. The threshold of ΔPPV(6-8) exceeding 2% identified responders with a sensitivity of 83% (95% CI 0.45 to 1.0, <i>p</i> < 0.0001) and a specificity of 73% (95% CI 0.48 to 1.0, <i>p</i> < 0.0001). The parameter ΔSVV(6-8) also revealed good predictive ability, reflected by an AUC of 0.82 (95% CI 0.67 to 0.94, <i>p</i> < 0.0001). The criterion ΔSVV(6-8) greater than 2% pinpointed responders with a sensitivity of 83% (95% CI 0.71 to 1.0, <i>p</i> < 0.001) and a specificity of 77% (95% CI 0.44 to 1.0, <i>p</i> < 0.001). <b>Conclusions</b>: This study demonstrates that VtC possesses good predictive ability for fluid responsiveness in patients undergoing general surgery.