Pressure-volume curves in the management of acute respiratory distress syndrome.

The interpretation of P-V curves is uncertain for several reasons: the influence of chest wall compliance, differences in regional lung compliance and intrapulmonary gas distribution, lung volume history, lung recruitment beyond the LIP, peripheral airway fluid movement, expiratory-flow limitation, differences between inflation and deflation limb characteristics, and interobserver variability in curve analysis. In addition, many studies of acute lung injury have constructed P-V curves following disconnection from the ventilator. The inevitable lung volume changes that occur may alter the elastic and viscoelastic behavior so that the resulting P-V curve characteristics may not accurately reflect conditions during mechanical ventilation. More extensive research seems to be required before P-V curves are used as a routine guide for mechanical ventilation therapy in ARDS. Furthermore, this article suggests that titrating PEEP or VT according to the inflation-limb P-V curve should be done with caution, because the mechanical significance of this information is open to question. Current research suggests the possibility that PEEP could be targeted according to the slope of deflation-limb compliance, because this measure may more accurately reflect global alveolar closing pressures. This type of analysis can be done only by transferring data into software programs that can perform sophisticated curve fitting, and such programs are not readily available to most clinicians. From a practical standpoint, there is no compelling clinical evidence that adjusting mechanical ventilation according to the P-V curve improves mortality or morbidity in ARDS as much or more than can be achieved simply by decreasing the VT and Pplat.