Pleural effusion complicates monitoring of respiratory mechanics*

Abstract

When pleural effusion is present, respiratory mechanics must be interpreted cautiously and sufficient positive end-expiratory pressure should be applied to prevent extensive collapse and intratidal cycles of recruitment/derecruitment.

Pleural Effusion in Patients With Acute Lung Injury

“…However, there is no reason why pleural effusion should change the intrinsic mechanical characteristics either of the chest wall or of the lung. In fact, we may consider the pleural effusion just a pressure generator which drives the chest wall (including the diaphragm) pushing it outward and the lung pushing it inward (6,17,26).…”

PEEP Titration: New Horizons

“…Computed tomography data suggest that PEEP recruited dependent lung units in the ipsilateral and contralateral lungs and decreased tidal recruitment in areas directly compressed by effusion. 30 These changes were not evident on static compliance measurements, suggesting that FRC improvement may be a better marker of optimal PEEP in this setting.…”

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

“…For example, estimates of P TP based on Pes measurements are almost certain to imprecisely represent all stresses within an asymmetrically compromised lung [11]. Th e volumealtering eff ects of unilat eral pleural eff usion were radically diff erent for the two lungs of experimental animals, and yet the calculated P TP was little aff ected by fl uid instillation [11].…”

“…Whether in obstructive disease, ALI/ARDS, or other volumereduced states (e.g., surgical reduction of lung tissue, eff usion-compressed lung), knowledge of FRC also enables calculation of specifi c resistance and provides better information regarding airway status [43,44]. Additionally, non-symmetrical disorders of the chest wall (e.g., unilateral pleural eff usion and increased IAP) may cause P TP and FRC to dissociate from each other [11]. Such dissociation may also be characteristic of some other lung disorders (e.g., secretion plugging, unilateral pneumonia, atele ctasis, embolism, pneumothorax, etc.).…”

“…Additionally, Pes represents the least positive local pressure along its own horizontal (gravitational) plane in the upright position [4]; even with position unchanged, absolut e P TP values elsewhere in the chest are the oretically diff erent. For such reasons, the ability of Pes to track global average changes in pleural pressure may be limited when supine and in the presence of asymmetrical lung disease [11].…”