Functional residual capacity and absolute lung volume

PURPOSE OF REVIEW: 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. RECENT FINDINGS: 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. SUMMARY: In conclusion, measuring FRC could be extremely valuable during mechanical ventilation, but clinical studies are needed to prove whether this technique will improve outcome.