title: Pulse pressure variations to predict fluid responsiveness: influence of tidal volume.
abstract: OBJECTIVE
  To evaluate the influence of tidal volume on the capacity of pulse pressure variation (DeltaPP) to predict fluid responsiveness.
  
  
  METHODS
  Prospective interventional study.
  
  
  METHODS
  A 31-bed university hospital medico-surgical ICU.
  
  
  METHODS
  Sixty mechanically ventilated critically ill patients requiring fluid challenge, separated according to their tidal volume.
  
  
  METHODS
  Fluid challenge with either 1,000 ml crystalloids or 500 ml colloids.
  
  
  RESULTS
  Complete hemodynamic measurements including DeltaPP were obtained before and after fluid challenge. Tidal volume was lower than 7 ml/kg in 26 patients, between 7-8 ml/kg in 9 patients, and greater than 8 ml/kg in 27 patients. ROC curve analysis was used to evaluate the predictive value of DeltaPP at different tidal volume thresholds, and 8 ml/kg best identified different behaviors. Overall, the cardiac index increased from 2.66 (2.00-3.47) to 3.04 (2.44-3.96) l/min m(2) ( P <0.001). It increased by more than 15% in 33 patients (fluid responders). Pulmonary artery occluded pressure was lower and DeltaPP higher in responders than in non-responders, but fluid responsiveness was better predicted with DeltaPP (ROC curve area 0.76+/-0.06) than with pulmonary artery occluded pressure (0.71+/-0.07) and right atrial (0.56+/-0.08) pressures. Despite similar response to fluid challenge in low (<8 ml/kg) and high tidal volume groups, the percent of correct classification of a 12% DeltaPP was 51% in the low tidal volume group and 88% in the high tidal volume group.
  
  
  CONCLUSIONS
  DeltaPP is a reliable predictor of fluid responsiveness in mechanically ventilated patients only when tidal volume is at least 8 ml/kg.
authors.affiliation: Department of Intensive Care, Erasme University Hospital of the Free University of Brussels, Route de Lennik 808, 1070 Brussels, Belgium. ddebacke@ulb.ac.be
authors.forename: Daniel
authors.initials: D
authors.lastname: De Backer
authors.forename: Sarah
authors.initials: S
authors.lastname: Heenen
authors.forename: Michael
authors.initials: M
authors.lastname: Piagnerelli
authors.forename: Marc
authors.initials: M
authors.lastname: Koch
authors.forename: Jean-Louis
authors.initials: JL
authors.lastname: Vincent
mesh_terms: D000368:Aged; D001530:Belgium; D001794:Blood Pressure / Q000502:physiology*; D002302:Cardiac Output; D003422:Critical Care; D005260:Female; D005440:Fluid Therapy / Q000379:methods*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012372:ROC Curve; D012121:Respiration, Artificial; D012128:Respiratory Distress Syndrome / Q000628:therapy; D013990:Tidal Volume / Q000502:physiology*