title: The occlusion tests and end-expiratory esophageal pressure: measurements and comparison in controlled and assisted ventilation.
abstract: BACKGROUND
  Esophageal pressure is used as a reliable surrogate of the pleural pressure. It is conventionally measured by an esophageal balloon placed in the lower part of the esophagus. To validate the correct position of the balloon, a positive pressure occlusion test by compressing the thorax during an end-expiratory pause or a Baydur test obtained by occluding the airway during an inspiratory effort is used. An acceptable catheter position is defined when the ratio between the changes in esophageal and airway pressure (∆Pes/∆Paw) is close to unity. Sedation and paralysis could affect the accuracy of esophageal pressure measurements. The aim of this study was to evaluate, in mechanically ventilated patients, the effects of paralysis, two different esophageal balloon positions and two PEEP levels on the ∆Pes/∆Paw ratio measured by the positive pressure occlusion and the Baydur tests and on the end-expiratory esophageal pressure and respiratory mechanics (lung and chest wall).
  
  
  METHODS
  Twenty-one intubated and mechanically ventilated patients (mean age 64.8 ± 14.0 years, body mass index 24.2 ± 4.3 kg/m(2), PaO2/FiO2 319.4 ± 117.3 mmHg) were enrolled. In step 1, patients were sedated and paralyzed during volume-controlled ventilation, and in step 2, they were only sedated during pressure support ventilation. In each step, two esophageal balloon positions (middle and low, between 25-30 cm and 40-45 cm from the mouth) and two levels of PEEP (0 and 10 cmH2O) were applied. The ∆Pes/∆Paw ratio and end-expiratory esophageal pressure were evaluated.
  
  
  RESULTS
  The ∆Pes/∆Paw ratio was slightly higher (+0.11) with positive occlusion test compared with Baydur's test. The level of PEEP and the esophageal balloon position did not affect this ratio. The ∆Pes and ∆Paw were significantly related to a correlation coefficient of r = 0.984 during the Baydur test and r = 0.909 in the positive occlusion test. End-expiratory esophageal pressure was significantly higher in sedated and paralyzed patients compared with sedated patients (+2.47 cmH2O) and when esophageal balloon was positioned in the low position (+2.26 cmH2O). The esophageal balloon position slightly influenced the lung elastance, while the PEEP reduced the chest wall elastance without affecting the lung and total respiratory system elastance.
  
  
  CONCLUSIONS
  Paralysis and balloon position did not clinically affect the measurement of the ∆Pes/∆Paw ratio, while they significantly increased the end-expiratory esophageal pressure.
authors: Dipartimento di Anestesia, Rianimazione (Intensiva e Subintensiva) e Terapia del Dolore, Fondazione IRCCS Ca' Granda - Ospedale Maggiore Policlinico, Via F. Sforza 35, Milan, Italy. chiumello@libero.it.|Dipartimento di Fisiopatologia Medico-Chirurgica e dei Trapianti, Università degli Studi di Milano, Milan, Italy. chiumello@libero.it.
authors: Davide
authors: D
authors: Chiumello
authors: Unità Operativa di Epidemiologia, Fondazione IRCCS Ca' Granda-Ospedale Maggiore Policlinico, Milan, Italy.
authors: Dario
authors: D
authors: Consonni
authors: Dipartimento di Anestesia, Rianimazione (Intensiva e Subintensiva) e Terapia del Dolore, Fondazione IRCCS Ca' Granda - Ospedale Maggiore Policlinico, Via F. Sforza 35, Milan, Italy.|Dipartimento di Fisiopatologia Medico-Chirurgica e dei Trapianti, Università degli Studi di Milano, Milan, Italy.
authors: Silvia
authors: S
authors: Coppola
authors: Dipartimento di Anestesia, Rianimazione (Intensiva e Subintensiva) e Terapia del Dolore, Fondazione IRCCS Ca' Granda - Ospedale Maggiore Policlinico, Via F. Sforza 35, Milan, Italy.|Dipartimento di Fisiopatologia Medico-Chirurgica e dei Trapianti, Università degli Studi di Milano, Milan, Italy.
authors: Sara
authors: S
authors: Froio
authors: Dipartimento di Fisiopatologia Medico-Chirurgica e dei Trapianti, Università degli Studi di Milano, Milan, Italy.
authors: Francesco
authors: F
authors: Crimella
authors: Dipartimento di Fisiopatologia Medico-Chirurgica e dei Trapianti, Università degli Studi di Milano, Milan, Italy.
authors: Andrea
authors: A
authors: Colombo
keywords: ARDS; Esophageal pressure; PEEP; Respiratory mechanics; Transpulmonary pressure