Pulse pressure variation predicts fluid responsiveness during general anesthesia
MedWire News: The gray zone approach applied to pulse pressure variation (PPV) is an accurate predictor of fluid responsiveness during general anesthesia, suggest study findings.
Respiratory arterial PPV is the best predictor of fluid responsiveness in mechanically ventilated patients during general anesthesia. However, previous studies determining a single cutoff point for responders (patients who will benefit from additional fluid loading) and non-responders have been conducted in a small numbers of patients.
To further test the predictive value of PPV, Maxime Cannesson (University of California, Irvine, USA) and co-authors studied 413 patients in four centers during general anesthesia and mechanical ventilation. PPV, central venous pressure, and cardiac output (CO) were recorded before and after volume expansion (VE). Response to VE was defined as more than a 15% increase in cardiac output.
In addition, the team applied the 'gray zone' approach to assess diagnostic accuracy of PPV for the prediction of fluid responsiveness using two cutoffs: one that with near certainty identifies non-responders and another cutoff that with near-certainty identifies responders. The impact of changes in the benefit-risk balance of VE on the gray zone were then evaluated.
A significant relationship was seen between PPV at baseline and percent change in CO induced by VE, suggesting that the higher the PPV value, the bigger the increase in CO induced by VE.
When response to VE was defined as an increase in CO greater than 15%, 51% of patients were responders and 49% were non-responders.
PPV was confirmed as significantly better for predicting fluid responsiveness compared with central venous pressure, with corresponding area under receiver operating characteristic curve values of 0.89 versus 0.57, respectively.
The PPV gray zone ranged from 9% to 13%, with 24% of patients falling within these limits. When the team assessed changes in gray zone limits, comparing tight fluid control versus liberal fluid control, the gray zones changed to 11-14% and 8-11%, respectively.
When the researchers assessed changes in gray zone limits according to the increase in CO considered clinically significant after fluid loading, the width of the gray zones was relatively conserved among the range of values tested to define fluid responsiveness. Indeed, if an increase of 7% in CO were considered clinically relevant, the gray zone for PPV would no longer be 9-13% (as calculated for an increase of 15%) but 5-8%.
In an associated editorial, Stefan De Hert (Ghent University, Belgium) said: "The gray zone approach introduces a new conceptual way of looking at PPV that is more in line with the physiologic hemodynamic principles and clinical reality than using a single cutoff value."
"It is to be expected that this new approach of assessing diagnostic accuracy of dynamic variables of fluid responsiveness will be of great help in future clinical decision-making."
By Ingrid Grasmo