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

Abstract The plethysmography variability index (PVI) is a safe, non-invasive, and useful parameter for evaluating fluid responsiveness but it does not reliably predict fluid responsiveness during low tidal volume (VT) ventilation. We hypothesized that in a ‘tidal volume challenge’ with a transient increase in tidal volume from 6 to 8 ml/kg, the changes in PVI will predict fluid responsiveness. We performed a prospective interventional study in adult patients undergoing hepatobiliary pancreatic tumor resections, having continuous cardiac output monitoring, and receiving controlled low VT ventilation. We recorded the values for PVI, perfusion index, corrected flow time (FTc), index of contractility (ICON), stroke volume variation, and stroke volume index at VT of 6 ml/kg and 1 min after the VT challenge. The VT was reduced to 6 ml/kg and a fluid bolus was given to identify fluid responders. The area under the receiver operating characteristic curve (AUC) for absolute change in PVI after increasing VT from 6 to 8 ml/kg was 0.86 (p-value < 0.001) with best cut-off value 2.5% with 95% sensitivity and 68% specificity after doing the tidal volume challenge. AUC for ICON and FTc at VT 8 ml/kg were 0.72 and 0.70 with p-value 0.008 and 0.01 and best cut-off values 40.7% and 332ms respectively. Changes in PVI value obtained by transiently increasing VT are superior to PVI value measured alone for predicting fluid responsiveness during low-VT ventilation. Also, ICON and FTc can be used as good and reliable predictors of fluid responsiveness.