title: In vivo calibration of esophageal pressure in the mechanically ventilated patient makes measurements reliable.
abstract: BACKGROUND
  Esophageal pressure (Pes) can provide information to guide mechanical ventilation in acute respiratory failure. However, both relative changes and absolute values of Pes can be affected by inappropriate filling of the esophageal balloon and by the elastance of the esophagus wall. We evaluated the feasibility and effectiveness of a calibration procedure consisting in optimization of balloon filling and subtraction of the pressure generated by the esophagus wall (Pew).
  
  
  METHODS
  An esophageal balloon was progressively filled in 36 patients under controlled mechanical ventilation. VBEST was the filling volume associated with the largest tidal increase of Pes. Esophageal wall elastance was quantified and Pew was computed at each filling volume. Different filling strategies were compared by performing a validation occlusion test.
  
  
  RESULTS
  Fifty series of measurements were performed. VBEST was 3.5 ± 1.9 ml (range 0.5-6.0). Esophagus elastance was 1.1 ± 0.5 cmH2O/ml (0.3-3.1). Both Pew and the result of the occlusion test differed among filling strategies. At filling volumes of 0.5, VBEST and 4.0 ml respectively, Pew was 0.0 ± 0.1, 2.0 ± 1.9, and 3.0 ± 1.7 cmH2O (p < 0.0001), whereas the occlusion test was satisfactory in 22%, 98%, and 88% of cases (p < 0.0001).
  
  
  CONCLUSIONS
  Under mechanical ventilation, an increase of balloon filling above the conventionally recommended low volumes warrants complete transmission of Pes swings, but is associated with significant elevation of baseline. A simple calibration procedure allows finding the filling volume associated with the best transmission of tidal Pes change and subtracting the associated baseline artifact, thus making measurement of absolute values of Pes reliable.
authors.affiliation: Anesthesia and Intensive Care, Emergency Department, Fondazione IRCCS Policlinico S. Matteo, Pavia, Italy. francesco.mojoli@unipv.it.|Anesthesia, Intensive Care and Pain Therapy, Department of Clinical, Surgical, Diagnostic and Pediatric Sciences, University of Pavia, Pavia, Italy. francesco.mojoli@unipv.it.
authors.forename: Francesco
authors.initials: F
authors.lastname: Mojoli
authors.affiliation: Anesthesia and Intensive Care, Emergency Department, Fondazione IRCCS Policlinico S. Matteo, Pavia, Italy.
authors.forename: Giorgio Antonio
authors.initials: GA
authors.lastname: Iotti
authors.affiliation: Anesthesia, Intensive Care and Pain Therapy, Department of Clinical, Surgical, Diagnostic and Pediatric Sciences, University of Pavia, Pavia, Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: Torriglia
authors.affiliation: Anesthesia and Intensive Care, Emergency Department, Fondazione IRCCS Policlinico S. Matteo, Pavia, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Pozzi
authors.affiliation: Anesthesia and Intensive Care, Department of Morphology, Surgery and Experimental Medicine, University of Ferrara, Arcispedale Sant'Anna, Ferrara, Italy.
authors.forename: Carlo Alberto
authors.initials: CA
authors.lastname: Volta
authors.affiliation: Anesthesia, Intensive Care and Pain Therapy, Department of Clinical, Surgical, Diagnostic and Pediatric Sciences, University of Pavia, Pavia, Italy.
authors.forename: Stefania
authors.initials: S
authors.lastname: Bianzina
authors.affiliation: Anesthesia and Intensive Care, Emergency Department, Fondazione IRCCS Policlinico S. Matteo, Pavia, Italy.|Anesthesia, Intensive Care and Pain Therapy, Department of Clinical, Surgical, Diagnostic and Pediatric Sciences, University of Pavia, Pavia, Italy.
authors.forename: Antonio
authors.initials: A
authors.lastname: Braschi
authors.affiliation: Keenan Research Centre, Li Ka Shing Knowledge Institute, St. Michael's Hospital, Toronto, ON, Canada.|Interdepartmental Division of Critical Care Medicine, University of Toronto, Toronto, ON, Canada.
authors.forename: Laurent
authors.initials: L
authors.lastname: Brochard
mesh_terms: D002138:Calibration / Q000592:standards*; D004947:Esophagus / Q000473:pathology*; D006801:Humans; D008991:Monitoring, Physiologic / Q000379:methods*; D011175:Positive-Pressure Respiration / Q000379:methods; D011312:Pressure; D012121:Respiration, Artificial / Q000379:methods; D015656:Respiratory Mechanics / Q000502:physiology
keywords: Calibration; Esophageal artifact; Esophageal balloon catheter; Esophageal elastance; Esophageal pressure; Mechanical ventilation; Pleural pressure; Protective ventilation; Transpulmonary pressure; Ventilator-induced lung injury