The Accuracy of the Oxygen Washout Technique for Functional Residual Capacity Assessment During Spontaneous Breathing

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Abstract

BACKGROUND:

Measurement of functional residual capacity (FRC) is of considerable interest for monitoring patients with lung injury. The lack of instruments has impeded routine bedside FRC measurement. Recently, a simple automated method for FRC assessment by O2 washout has been introduced. We designed this study to evaluate the accuracy of FRC measurement using the O2 washout technique.

METHODS:

The LUFU system (Draeger, Luebeck, Germany) estimates FRC by O2 washout, a variant of multiple breath nitrogen washout. This technique uses a sidestream O2-analyzer to calculate FRC from end-inspired and end-expired O2 concentrations during fast changes of Fio2. We measured FRC in 23 healthy, spontaneously breathing volunteers in the sitting position using three techniques: 1) helium dilution (FRC-He), 2) body plethysmography (FRC-bp), 3) oxygen washout (FRC-O2).

RESULTS:

FRC-O2 (mean 4.1 ± 1.1 L, range 2.4–6.9 L) corresponds with FRC-He (mean 4.0 ± 1.0 L, range 2.4–6.2 L; bias of FRC-O2: −0.2 ± 0.4 L) and FRC-bp (mean 4.2 ± 1.0 L, range 2.8–6.1 L; bias of FRC-O2: 0.1 ± 0.6 L).

CONCLUSIONS:

The bias and precision of the O2 washout technique using the LUFU system were clinically acceptable when compared with FRC-He and FRC-bp for FRC assessment in spontaneously breathing volunteers.

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