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TECHNOLOGY, COMPUTING, AND SIMULATION

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

Hermann Heinze, MD^*, Bernhard Schaaf, MD, Jochen Grefer, MD^*, Karl Klotz, MD^*, and Wolfgang Eichler, MD^*

From the Departments of *Anesthesiology and Medicine III, University of Luebeck, Luebeck, Germany.

Address correspondence and reprint requests to Hermann Heinze, MD, Department of Anesthesiology, University of Luebeck, Ratzeburger Allee 160, 23538 Luebeck, Germany. Address e-mail to Hermannheinze{at}ngi.de.

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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