To evaluate the efficacy of individualized mini-fluid challenge test in determining the fluid responsiveness in the patients undergoing surgery in prone position.

A total of 47 patients of either sex, aged > 18 yr, with boy mass index of 18-30 kg/m^2, of American Society of Anesthesiologists Physical Status classification Ⅰ or Ⅱ, undergoing elective spinal surgery in prone position, were included. The volume-controlled mode was used for mechanical ventilation, and the tidal volume was set at 8 ml/kg. The hemodynamic parameters were monitored by FloTrac/Vigileo system. The patient was changed to prone position at 5 min after endotracheal intubation (T₁), hydroxyethyl starch 130/0.4 sodium chloride injection 2 ml/kg was intravenously given at 5 min of prone position (T₂), and fluid 3 ml/kg was continuously infused at 1 min after 2 ml/kg fluid infusion (T₃), and both infusion rates were 0.5 ml·kg^-1·min^-1. A mini-fluid challenge test was performed during T₂-T₃ period, the standard volume therapy (total infusion of liquid 5 ml/kg) was carried out from T₂ to 1 min after infusion of liquid 3 ml/kg (T₄). The rate of change in SV at T₃ time point (ΔSVT₃) was calculated relative to T₂ time point, and the rate of change in SV at T₄ time point (ΔSVT₄) was calculated relative to T₂ time point. Positive fluid responsiveness test was defined as an increase in ΔSVT₄≥10%, and patients were divided into volume response group (Rs group) and non-volume response group (NRs group). ΔSVT₃, ΔSVT₄ and stroke volume variation and pulse pressure variation at T₃ and T₄ time points were selected, the receiver operating characteristic curve predicting fluid responsiveness was generated, and the area under the receiver operating characteristic curve (AUC) was calculated.

Forty-one patients were finally enrolled, including 18 cases in Rs group and 23 cases in NRs group. The AUC of ΔSVT₃ determining fluid responsiveness was 0.976, with the sensitivity 0.944 and specificity 0.957. The AUC of ΔSVT₄ determining fluid responsiveness was 0.971, with sensitivity 0.889 and specificity 0.95. The AUC of stroke volume variation at T₃ and T₄ in predicting fluid responsiveness was 0.632 and 0.609, respectively. The AUC of pulse pressure variation at T₃ and T₄ predicting fluid responsiveness was 0.470 and 0.380, respectively.

Individualized mini-fluid challenge test (2 mg/kg colloidal solution) can accurately determine the fluid responsiveness in the patients undergoing surgery in prone position.

Fluid therapy; Prone position; Vascular capacitance