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

Abstract

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.

Lung stress and strain calculations in mechanically ventilated patients in the intensive care unit

“…A PEEP of 15 cmH 2 O was applied for 15 min to achieve a steady‐state situation, by means of a stable carbon dioxide volume (VCO 2 ) signal for at least 10 min. Steady state was based on VCO 2 as this is the main parameter in the formula to calculate EELV,4 which is integrated in the Engström Care station. The first PEEP level was set to 15 cmH 2 O to avoid peak inspiratory pressures above 30 cmH 2 O.…”

“…We measured EELV using the NMBW technique devised by Olegard et al 4. The Engström Carestation ventilator is equipped with an integrated COVX module, which delivers data required to calculate EELV.…”

Measurement of Alveolar Recruitment at the Bedside: The Beginning of a New Era in Respiratory Monitoring?

“…16 The PEEP releasing maneuver is replaced by the measurement of endexpiratory lung volume using the nitrogen wash-out/ wash-in technique. 17,18 The ventilator is equipped with a sensor specifically designed for measuring intratracheal pressure. By excluding inspiratory resistance of the endotracheal tube, measuring intratracheal pressure makes possible the accurate measurement of dynostatic PV curves in dynamic conditions.…”

Regional lung derecruitment after endotracheal suction during volume- or pressure-controlled ventilation: a study using electric impedance tomography

“…A modified technique of nitrogen (N 2 ) washout/washin by a stepwise change in FiO 2 was used to measure FRC [92]. By increasing FiO 2 by 10 % and then by lowering it again, an FRC value was obtained by dividing the washout/washin volume of N 2 with the change in fraction (∆F) of N 2 (FRC N2 ).…”

“…The nitrogen washout/washin method for FRC measurements used (Papers III and IV) is new but promising and evaluated in a number of studies [87,92]. It is computerized and currently in clinical use, incorporated into modern ventilators and therefore suitable for our studies.…”