title: Pulse Pressure Variation Adjusted by Respiratory Changes in Pleural Pressure, Rather Than by Tidal Volume, Reliably Predicts Fluid Responsiveness in Patients With Acute Respiratory Distress Syndrome.
abstract: OBJECTIVE
  1) To evaluate the ability of pulse pressure variation adjusted by respiratory changes in pleural pressure to predict fluid responsiveness compared with pulse pressure variation alone. 2) To identify factors explaining the poor performance of pulse pressure variation in acute respiratory distress syndrome.
  
  
  METHODS
  Prospective study.
  
  
  METHODS
  Forty-bed university hospital general ICU.
  
  
  METHODS
  Ninety-six mechanically ventilated acute respiratory distress syndrome patients requiring fluid challenge.
  
  
  METHODS
  Fluid challenge, 500 mL saline over 20 minutes.
  
  
  RESULTS
  Before fluid challenge, esophageal pressure was measured at the end-inspiratory and end-expiratory occlusions. Change in pleural pressure was calculated as the difference between esophageal pressure measured at end-inspiratory and end-expiratory occlusions. Hemodynamic measurements were obtained before and after the fluid challenge. Patients were ventilated with tidal volume 7.0 ± 0.8 mL/kg predicted body weight. The fluids increased cardiac output by greater than 15% in 52 patients (responders). Adjusting pulse pressure variation for changes in pleural pressure (area under the receiver operating characteristic curve, 0.94 [0.88-0.98]) and the ratio of chest wall elastance to total respiratory system elastance (area under the receiver operating characteristic curve, 0.93 [0.88-0.98]) predicted fluid responsiveness better than pulse pressure variation (area under the receiver operating characteristic curve, 0.78 [0.69-0.86]; all p < 0.01). The gray zone approach identified a range of pulse pressure variation/changes in pleural pressure values (1.94-2.1) in 3.1% of patients for whom fluid responsiveness could not be predicted reliably. On logistic regression analysis, two independent factors affected the correct classification of fluid responsiveness at a 12% pulse pressure variation cutoff: tidal volume (adjusted odds ratio 1.57/50 mL; 95% CI, 1.05-2.34; p = 0.027) and chest wall elastance/respiratory system elastance (adjusted odds ratio, 2.035/0.1 unit; 95% CI, 1.36-3.06; p = 0.001). In patients with chest wall elastance/respiratory system elastance above the median (0.28), pulse pressure variation area under the receiver operating characteristic curve was 0.94 (95% CI, 0.84-0.99) compared with 0.76 (95% CI, 0.61-0.87) otherwise (p = 0.02).
  
  
  CONCLUSIONS
  In acute respiratory distress syndrome patients, pulse pressure variation adjusted by changes in pleural pressure is a reliable fluid responsiveness predictor despite the low tidal volume (< 8 mL/kg). The poor predictive ability of pulse pressure variation in acute respiratory distress syndrome patients is more related to low chest wall elastance/respiratory system elastance ratios than to a low tidal volume.
authors.affiliation: 1Graduate School of Tianjin Medical University, Tianjin, China. 2Medical Intensive Care Unit, Pingjin Hospital, Logistics College of the Chinese People's Armed Police Forces, Tianjin, China. 3Surgical Intensive Care Unit, Pingjin Hospital, Logistics College of the Chinese People's Armed Police Forces, Tianjin, China. 4Tianjin Key Laboratory of Cardiovascular Remodeling and Target Organ Injury, Institute of Cardiovascular Disease and Heart Center, Pingjin Hospital, Logistics College of the Chinese People's Armed Police Forces, Tianjin, China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Liu
authors.forename: Lu-qing
authors.initials: LQ
authors.lastname: Wei
authors.forename: Guo-qiang
authors.initials: GQ
authors.lastname: Li
authors.forename: Xin
authors.initials: X
authors.lastname: Yu
authors.forename: Guo-feng
authors.initials: GF
authors.lastname: Li
authors.forename: Yu-ming
authors.initials: YM
authors.lastname: Li
mesh_terms: D005260:Female; D005440:Fluid Therapy / Q000379:methods*; D006439:Hemodynamics; D006785:Hospitals, University; D006801:Humans; D007362:Intensive Care Units; D008297:Male; D011446:Prospective Studies; D012121:Respiration, Artificial / Q000379:methods*; D012128:Respiratory Distress Syndrome / Q000628:therapy*; D015656:Respiratory Mechanics / Q000502:physiology*