The Impact of Different Step Changes of Inspiratory Fraction of Oxygen on Functional Residual Capacity Measurements Using the Oxygen Washout Technique in Ventilated Patients

Abstract

Functional residual capacity (FRC) measurements may help to guide respiratory therapy. Using the oxygen washout technique, FRC can be assessed at bedside during spontaneous breathing. High repeatability, crucial for monitoring, has not been shown in ventilated patients. A large step change of inspiratory fraction of oxygen (FiO(2)) (DeltaFiO(2)) may impede the clinical use in patients ventilated with high FiO(2). We investigated the repeatability of FRC measurements and the impact of different DeltaFiO(2) on this repeatability. The LUFU system (Draeger Medical, Luebeck, Germany) estimates FRC by oxygen washout, a variant of multiple-breath-nitrogen-washout during a fast DeltaFiO(2). In 20 postoperative cardiac surgery patients, FRC was measured in duplicate using DeltaFiO(2) of 0.1, 0.2, and 0.6. There were no differences between repeated measurements of FRC, neither using a DeltaFiO(2) of 0.1, 0.2 nor 0.6(Delta0.1: 2.62 L +/- 0.58, 2.62 L +/- 0.59, P = 0.995; Delta0.2: 2.70 L +/- 0.59, 2.66 L +/- 0.56, P = 0.258; Delta0.6: 2.61 L +/- 0.58, 2.59 L +/- 0.58, P = 0,639). Coefficients of variation were 6.6%, 5.6%, and 6.6%, respectively. FRC can be measured in ventilated patients using the oxygen washout technique with a clinically acceptable repeatability. Repeatability is not significantly influenced whether using a DeltaFiO(2) of 0.1, 0.2, or 0.6.