title: Prone position affects stroke volume variation performance in predicting fluid responsiveness in neurosurgical patients.
abstract: BACKGROUND
  Stroke volume variation (SVV) during mechanical ventilation predicts preload responsiveness. We hypothesized that the prone position would alter the performance of this dynamic indicator.
  
  
  METHODS
  Two parallel groups of ventilated neurosurgical patients with low tidal volume (6-8 ml.kg-1) were studied before surgical incision. SVV was measured at T0, T15 and T30 min during a fluid volume expansion (250 mL hetastarch 6% over 30 min) with patients in either the supine (N.=29; Supine group) or prone position (N.=23; Prone group). Fluid responsiveness was defined as an increase in the stroke volume index (SVI) of ≥20% at T30. Receiver-operating characteristics (ROC) curves were generated for SVV.
  
  
  RESULTS
  Prone positioning significantly increased SVV. Volume expansion in the Prone group increased SVI but led to a decline in SVV from 16% (12-22; median, 25-75th percentile) at T0 to 9% (8-13%) at T30. These effects on SVI and SVV were more pronounced compared to those obtained in the Supine group (P ≤0.05). Fluid responsiveness was predicted by SVV >12% at T0 (sensitivity 88%, specificity 62%) in the Supine group. In the Prone group, the area under the ROC curve of SVV (0.53; 95% confidence interval 0.27-0.79) did not allow the determination of a threshold SVV value.
  
  
  CONCLUSIONS
  In ventilated patients with low tidal volume, a prone position may have a direct effect on the heart that alters the performance of SVV in predicting fluid responsiveness. External factor such as prone position renders difficult the interpretation of SVV as a dynamic indicator of cardiac preload.
authors.affiliation: Department of Anesthesia and Critical Care, Michallon Hospital, and Joseph Fourier University, Grenoble, France - jfpayen@ujf-grenoble.fr.
authors.forename: K
authors.initials: K
authors.lastname: Berger
authors.forename: G
authors.initials: G
authors.lastname: Francony
authors.forename: P
authors.initials: P
authors.lastname: Bouzat
authors.forename: C
authors.initials: C
authors.lastname: Halle
authors.forename: C
authors.initials: C
authors.lastname: Genty
authors.forename: M
authors.initials: M
authors.lastname: Oddoux
authors.forename: E
authors.initials: E
authors.lastname: Gay
authors.forename: P
authors.initials: P
authors.lastname: Albaladejo
authors.forename: J F
authors.initials: JF
authors.lastname: Payen
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D005440:Fluid Therapy / Q000379:methods*; D006801:Humans; D008297:Male; D008875:Middle Aged; D019635:Neurosurgical Procedures / Q000379:methods*; D016684:Prone Position; D011446:Prospective Studies; D012121:Respiration, Artificial; D013318:Stroke Volume; D016683:Supine Position; D013990:Tidal Volume