Esophageal pressures in acute lung injury: do they represent artifact or useful information about transpulmonary pressure, chest wall mechanics, and lung stress?

Abstract

Acute lung injury can be worsened by inappropriate mechanical ventilation, and numerous experimental studies suggest that ventilator-induced lung injury is increased by excessive lung inflation at end inspiration or inadequate lung inflation at end expiration. Lung inflation depends not only on airway pressures from the ventilator but, also, pleural pressure within the chest wall. Although esophageal pressure (Pes) measurements are often used to estimate pleural pressures in healthy subjects and patients, they are widely mistrusted and rarely used in critical illness. To assess the credibility of Pes as an estimate of pleural pressure in critically ill patients, we compared Pes measurements in 48 patients with acute lung injury with simultaneously measured gastric and bladder pressures (Pga and P(blad)). End-expiratory Pes, Pga, and P(blad) were high and varied widely among patients, averaging 18.6 +/- 4.7, 18.4 +/- 5.6, and 19.3 +/- 7.8 cmH(2)O, respectively (mean +/- SD). End-expiratory Pes was correlated with Pga (P = 0.0004) and P(blad) (P = 0.0104) and unrelated to chest wall compliance. Pes-Pga differences were consistent with expected gravitational pressure gradients and transdiaphragmatic pressures. Transpulmonary pressure (airway pressure - Pes) was -2.8 +/- 4.9 cmH(2)O at end exhalation and 8.3 +/- 6.2 cmH(2)O at end inflation, values consistent with effects of mediastinal weight, gravitational gradients in pleural pressure, and airway closure at end exhalation. Lung parenchymal stress measured directly as end-inspiratory transpulmonary pressure was much less than stress inferred from the plateau airway pressures and lung and chest wall compliances. We suggest that Pes can be used to estimate transpulmonary pressures that are consistent with known physiology and can provide meaningful information, otherwise unavailable, in critically ill patients.

Recruitment Maneuvers and PEEP Titration

“…This can result in an increase in pleural pressure, and if pleural pressure is high relative to alveolar pressure, there is a potential for alveolar collapse. 81 Thus, it may be desirable to set PEEP greater than end-expiratory pleural pressure. The use of an esophageal balloon to estimate pleural pressure has been advocated to allow a more precise setting of PEEP (Fig.…”

Respiratory Mechanics in Mechanically Ventilated Patients

“…The traditional approach to assess P pl is the use of an esophageal balloon, [11][12][13][14][15][16][17][18] which consists of a thin catheter with multiple small holes in the distal 5-7 cm of its length. A 10-cm-long balloon is placed over the distal end of the catheter to prevent the holes in the catheter from being occluded by esophageal tissue and secretions, and the balloon is inflated with a small amount of air (0.5 mL).…”

“…The weight of the heart can bias the P es by as much as 5 cm H 2 O. 16 The results of Guérin and Richard 21 suggest that referencing absolute P es values to those obtained at the relaxation volume of the respiratory system might improve the customization of the correction of P es based on the physiologic and individual context, rather than using an invariant value of 5 cm H 2 O.…”

Two Steps Forward in Bedside Monitoring of Lung Mechanics: Transpulmonary Pressure and Lung Volume

“…Other studies suggest Pes measurement as a physi ologically defensible and reliable tool for estimating P TP in critically ill patients [13,14,16]. As an ex ample of such enthusiastic reports, Grasso et al [16] evaluated whether keeping end-inspi ratory P TP within a theoretically innocuous range might allow safe increases of PEEP in pursuit of improved oxygenation.…”