Measurement of functional residual capacity and pulmonary carbon monoxide diffusing capacity during mechanical ventilation with PEEP.

First, our new simplified method to measure FRC and DLCO simultaneously during mechanical ventilation was described in detail. Secondly, we applied the method to ARDS patients and observed the effects of PEEP on arterial blood gases (ABGs), FRC and DLCO of these patients. As reported hitherto, FRC was consistently increased by PEEP, whereas ABGs in some cases were not necessarily improved with increase in FRC. DLCO/FRC remained unchanged, although DLCO increased with PEEP. We concluded that the dissociation of FRC and ABG data in a group of patients could be caused by wasted ventilation which might be attributed to VA/Q unevenness.