Effects of tidal volume challenge on the reliability of plethysmography variability index in hepatobiliary and pancreatic surgeries: a prospective interventional study

Background The plethysmography variability index (PVI) is a non-invasive, real-time, and automated parameter for evaluating fluid responsiveness, but it does not reliably predict fluid responsiveness during low tidal volume (V T ) ventilation. We hypothesized that in a ‘tidal volume challenge’ with a transient increase in tidal volume from 6 to 8 ml Kg − 1 , the changes in PVI could predict fluid responsiveness reliably. Method We performed a prospective interventional study in adult patients undergoing hepatobiliary or pancreatic tumor resections and receiving controlled low V T ventilation. The values for PVI, perfusion index, stroke volume variation, and stroke volume index (SVI) were recorded at baseline V T of 6 ml Kg − 1 , 1 min after the V T challenge (8 ml Kg − 1 ), 1 min after V T 6 ml Kg − 1 reduced back again, and then 5 min after crystalloid fluid bolus 6 ml kg − 1 (actual body weight) administered over 10 min. The fluid responders were identified by SVI rise ≥ 10% after the fluid bolus. Results The area under the receiver operating characteristic curve for PVI value change (ΔPVI 6–8 ) after increasing V T from 6 to 8 ml Kg − 1 was 0.86 (95% confidence interval, 0.76–0.96), P < 0.001, 95% sensitivity, 68% specificity, and with best cut-off value of absolute change (ΔPVI 6–8 ) = 2.5%. Conclusion In hepatobiliary and pancreatic surgeries, tidal volume challenge improves the reliability of PVI for predicting fluid responsiveness and changes in PVI values obtained after tidal volume challenge are comparable to the changes in SVI.