Assessment of Fluid Responsiveness in Prone Neurosurgical Patients Undergoing Protective Ventilation: Role of Dynamic Indices, Tidal Volume Challenge, and End-Expiratory Occlusion Test.

BACKGROUND: In patients in the prone position, the reliability of pulse pressure variation and stroke volume variation (PPV and SVV) and the use of functional hemodynamic tests to predict fluid responsiveness have not previously been established. Perioperatively, in this setting, optimizing fluid management can be challenging, and fluid overload is associated with both intraoperative and postoperative complications. We designed this study to assess the sensitivity and specificity of baseline PPV and SVV, the tidal volume (VT) challenge (VTC) and the end-expiratory occlusion test (EEOT) in predicting fluid responsiveness during elective spinal surgery. METHODS: The study protocol was started during a period of intraoperative hemodynamic stability after prone positioning and before the administration of any vasopressor: (1) at baseline, the controlled ventilation was set at 6 mL/kg of predicted body weight (PBW) (T0); (2) patients underwent the first EEOT (EEOT6) by interrupting the mechanical ventilation for 30 seconds; (3) the ventilation was set again at 6 mL/kg PBW for 1 minute (T1); (4) the VTC was applied by increasing the VT up to 8 mL/kg PBW for 1 minute; (5) the ventilation was kept at 8 mL/kg PBW for 1 minute (T2); (6) a second EEOT (EEOT8) was performed; (7) the VT was reduced back to 6 mL/kg PBW for 1 minute (T3); (8) a fluid challenge of 250 mL of Ringer's solution was infused over 10 minutes. After each step, a complete set of hemodynamic measurements was recorded. RESULTS: Neither PPV and SVV values recorded at T3 nor the EEOT6 or the EEOT8 predicted fluid responsiveness. The change in PPV after VTC application predicted fluid responsiveness with an area under the curve of 0.96 (95% confidence interval, 0.87-1.00), showing a sensitivity of 95.2% and a specificity of 94.7%, using a cutoff increase of 12.2%. The change in SVV after VTC application predicted fluid responsiveness with an area under the curve 0.96 (95% confidence interval, 0.89-1.00) showing a sensitivity of 95.2% and a specificity of 94.7%, using a cutoff increase of 8.0%. A linear correlation between stroke volume index changes after fluid challenge administration and the changes in PPV and SVV after VTC application was observed (r = 0.71; P < .0001 and r = 0.68; P < .0001, respectively). CONCLUSIONS: In prone elective neurosurgical patients, the baseline values of PPV and SVV and the EEOT fail to predict fluid responsiveness, while the VTC is a very reliable functional hemodynamic test and could be helpful in guiding intraoperative fluid therapy.

Tidal volume challenge to predict fluid responsiveness in the operating room: An observational study.

BACKGROUND: Pulse pressure variation (PPV) and stroke volume variation (SVV) do not predict fluid responsiveness when using a protective ventilation strategy: the use of functional haemodynamic tests can be useful to overcome this limitation. OBJECTIVES: We tested the use of a tidal volume challenge (VTC), during 6 ml kg [predicted body weight (PBW)] ventilation, and the end-expiratory occlusion test (EEOT) for prediction of fluid responsiveness. DESIGN: An interventional prospective study. SETTING: Supine elective neurosurgical patients. INTERVENTIONS: The study protocol was, first, the initial EEOT test was performed during baseline 6 ml kg PBW ventilation; second, VTC was performed by increasing the VT up to 8 ml kg PBW and PPV and SVV changes were recorded after 1 min; third, a second EEOT was performed during 8 ml kg PBW ventilation; and VT was reduced back to 6 ml kg PBW and a third EEOT was performed. Finally, a 250 ml fluid challenge was administered over 10 min to identify fluid responders (increase in stroke volume index ≥10%). RESULTS: In the 40 patients analysed, PPV and SVV values at baseline and EEOT performed at 6 ml kg PBW did not predict fluid responsiveness. A 13.3% increase in PPV after VTC predicted fluid responsiveness with a sensitivity of 94.7% and a specificity of 76.1%, while a 12.1% increase in SVV after VTC predicted fluid responsiveness with a sensitivity of 78.9% and a specificity of 95.2%. After EEOT performed at 8 ml kg PBW, a 3.6% increase in cardiac index predicted fluid responsiveness with a sensitivity of 89.4% and a specificity of 85.7%, while a 4.7% increase in stroke volume index (SVI) with a sensitivity of 89.4% and a specificity of 85.7%. CONCLUSION: The changes in PPV and SVV obtained after VTC are reliable and comparable to the changes in CI and SVI obtained after EEOT performed at 8 ml kg PBW in predicting fluid responsiveness in neurosurgical patients. TRIAL REGISTRATION: ACTRN12618000351213.