Automated pre-ejection period variation indexed to tidal volume predicts fluid responsiveness after cardiac surgery

Reliable continuous monitoring of fluid responsiveness is an unsolved issue in patients ventilated with low tidal volume. We hypothesised that variations in the pre-ejection period (PEP) defined as the time interval between electrocardiogram (ECG) R-wave and onset of systolic upstroke in arterial blood pressure could reliably predict fluid responsiveness in patients ventilated with moderately low tidal volume. Furthermore, we hypothesised that indexing dynamic parameters to tidal volume would improve their prediction. The aim was to refine and automate a previously suggested algorithm for PEP variation (Delta PEP) and to test this new parameter indexed to tidal volume (PEPV), as a marker of fluid responsiveness along with central venous pressure (CVP), pulse pressure variation (PPV) and Delta PEP. Additionally, the aim was to evaluate the concept of indexing dynamic parameters to tidal volume. Arterial pressure, CVP, ECG and cardiac index (CI) were acquired from 23 mechanically ventilated post-cardiac surgery patients scheduled for volume expansion. PEPV, PPV and Delta PEP were extracted. Using responder/non-responder classification (response=change in CI >+15%), sensitivity and specificity were 100% and 83%, respectively, for PEPV, 94% and 83% for Delta PEP, and 94% and 83% for PPV. CVP offered no relevant information. Tidal volume indexing improved sensitivity for Delta PEP to 100%. In this study in post-cardiac surgery patients, a refined parameter, PEPV, predicted fluid responsiveness better than PPV and Delta PEP. Our results suggest that dynamic parameters using variations in PEP should be indexed to tidal volume.