Estimation of functional residual capacity at the bedside using standard monitoring equipment: A modified nitrogen washout/washin technique requiring a small change of the inspired oxygen fraction

  • Olegård C
  • Söndergaard S
  • Houltz E
 et al. 
  • 37


    Mendeley users who have this article in their library.
  • 100


    Citations of this article.


We developed a modified nitrogen washin/washout technique based on standard monitors using inspiratory and end-tidal gas concentration values for functional residual capacity (FRC) measurements in patients with acute respiratory failure (ARF). For validation we used an oxygen-consuming lung model ventilated with an inspiratory oxygen fraction (Fio(2)) between 0.3 and 1.0. The respiratory quotient of the lung model was varied between 0.7 and 1.0. Measurements were performed changing Fio(2) with fractions of 0.1, 0.2, and 0.3. In 28 patients with ARF, duplicate measurements were performed. In the lung model, an Fio(2) change of 0.1 resulted in a value of 103 +/- 5% of the reference FRC value of the lung model, and the precision was equally good up to an Fio(2) of 1.0 with a value of 103 +/- 7%. In the patients, duplicate measurements showed a bias of -5 mL with a 95% confidence interval [-38; 29 mL ]. A comparison of a change in Fio(2) of 0.1 with 0.3 showed a bias of -9 mL and limits of agreement of [-365; 347 mL]. This study shows good precision of FRC measurements with standard monitors using a change in Fio(2) of only 0.1. Measurements can be performed with equal precision up to an Fio(2) of 1.0.

Get free article suggestions today

Mendeley saves you time finding and organizing research

Sign up here
Already have an account ?Sign in

Find this document


  • Cecilia Olegård

  • Sören Söndergaard

  • Erik Houltz

  • Stefan Lundin

  • Ola Stenqvist

Cite this document

Choose a citation style from the tabs below

Save time finding and organizing research with Mendeley

Sign up for free