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

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 (V T ) 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 V T 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 V T of 6 ml/kg and 1 min after the V T challenge. The V T 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 V T 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 V T 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 V T are superior to PVI value measured alone for predicting fluid responsiveness during low-V T ventilation. Also, ICON and FTc can be used as good and reliable predictors of fluid responsiveness.