title: Validation of pulse pressure variation and corrected flow time as predictors of fluid responsiveness in patients in the prone position.
abstract: BACKGROUND
  The aim of this prospective trial was to investigate the ability of pulse pressure variation (PPV) and corrected flow time (FTc) to predict fluid responsiveness in the prone position.
  
  
  METHODS
  Forty-four patients undergoing lumbar spine surgery in the prone position on a Wilson frame were prospectively studied. PPV and FTc were measured before and after a colloid bolus (6 ml kg(-1)) both in the supine and in the prone positions. Fluid responsiveness was defined as an increase in the stroke volume index of ≥ 10% as measured by oesophageal Doppler.
  
  
  RESULTS
  In the supine position, 26 patients were responders and the areas under the curve (AUC) of the receiver-operator characteristic (ROC) curves of PPV and FTc were 0.935 [95% confidence interval (CI): 0.870-0.999, P<0.001] and 0.822 (95% CI: 0.682-0.961, P<0.001), respectively. The optimal cut-off PPV and FTc values were 15% (sensitivity 73%, specificity 94%) and 358 ms (sensitivity 88%, specificity 78%), respectively. In the prone position, 34 patients were responders and the AUCs of PPV and FTc were 0.969 (95% CI: 0.912-1.000, P<0.001) and 0.846 (95% CI: 0.706-0.985, P=0.001), respectively. The optimal cut-off PPV and FTc values were 14% (sensitivity 97%, specificity 90%) and 331 ms (sensitivity 77%, specificity 90%), respectively.
  
  
  CONCLUSIONS
  While the predictability of PPV was significantly higher than that of FTc in the prone position, both variables showed high predictability and remained as useful indices for guiding fluid therapy in prone patients with minimal alterations in their optimal cut-off values to predict fluid responsiveness. Clinical trial registration URL: http://www.clinicaltrials.gov/ct2/show/NCT01646359?term=NCT01646359&rank=1 and unique identification number NCT01646359.
authors.affiliation: Department of Anaesthesiology and Pain Medicine, Chung-Ang University College of Medicine, Seoul, Republic of Korea.
authors.forename: S-Y
authors.initials: SY
authors.lastname: Yang
authors.forename: J-K
authors.initials: JK
authors.lastname: Shim
authors.forename: Y
authors.initials: Y
authors.lastname: Song
authors.forename: S-J
authors.initials: SJ
authors.lastname: Seo
authors.forename: Y-L
authors.initials: YL
authors.lastname: Kwak
mesh_terms: D000328:Adult; D000368:Aged; D001794:Blood Pressure / Q000502:physiology; D005260:Female; D005440:Fluid Therapy / Q000379:methods*; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D007430:Intraoperative Care / Q000379:methods; D008159:Lumbar Vertebrae / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods*; D016684:Prone Position / Q000502:physiology; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D013123:Spinal Fusion; D013318:Stroke Volume / Q000502:physiology; D016683:Supine Position / Q000502:physiology; D055815:Young Adult