Functional residual capacity and absolute lung volume.

Abstract

To discuss the role of measuring functional residual capacity (FRC) during mechanical ventilation to improve patient ventilator settings in order to prevent ventilator-induced lung injury. Nowadays, FRC can be measured without the use of tracer gases and without disconnection from the ventilator. It is shown that FRC can provide additional information to optimize the ventilator setting; for example, FRC measurements can differentiate between responders and nonresponders after a recruitment maneuver, and in combination with dynamic compliance one can differentiate between recruitment and overdistention during a positive end-expiratory pressure trial. In addition, FRC measurements enable not only to estimate stress and strain at the bedside, but also to estimate ventilation inhomogeneity. In conclusion, measuring FRC could be extremely valuable during mechanical ventilation, but clinical studies are needed to prove whether this technique will improve outcome.