Journal of Clinical Monitoring and Computing

, Volume 20, Issue 4, pp 251–260 | Cite as

Monitoring of Functional Residual Capacity by an Oxygen Washin/Washout; Technical Description and Evaluation

  • Dieter Weismann
  • Hajo Reißmann
  • Stefan Maisch
  • Bernd Füllekrug
  • Jochen Schulte


Objective. It was the goal of this study to develop and test an automated method for measuring functional residual capacity (FRC) by an oxygen washin/washout in intensive care settings. Such a method is required to work with conventional ventilator breathing systems and to use only medical grade sensors. Methods. The oxygen setting on a standard intensive care ventilator is changed by at least 10percnt;. Ventilatory pressure and flow are measured by the built-in sensors of the intensive care ventilator. Oxygen concentration is measured by a diverting medical oxygen analyzer. In order to overcome the known problem that synchrony between flow and concentration measurement is corrupted by the change of gas viscosity and by the cyclic change of airway pressure, a physical/mathematical model of the pneumatic circuit of the analyzer was developed. With this model, the change of sample flow is calculated continuously. Thus, synchrony between flow and gas concentration measurement is restored. This allows the determination of volumetric gas fluxes as needed for the FRC measurement. The setup was tested in the laboratory with a lung simulator. Simulated lung compliance, breathing frequency and tidal volume were varied. Results. The mean difference between measured and simulated FRC (range 1.7 to 5 L) was less than 1percnt; at tidal volumes greater than 400 mL. This difference ranged from −5percnt; to 8percnt;, depending on simulated lung compliance and ventilator setting. The variability of consecutive measurements was about 2.5percnt;. Conclusions. A method has been developed for reliable measurement of the FRC with an oxygen washin/washout technique. This method is sufficiently easy to use to suit for application in intensive care units. It does not require any action by the operator except a manual change of inspired oxygen concentration. Accuracy and sensitivity of the method have been proven sufficient to meet clinical and scientific requirements. Future clinical studies will reveal the applicability of the chosen procedure under clinical conditions.


functional residual capacity oxygen washin/washout mechanical ventilation 


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. 1.
    Hedenstierna G. The recording of FRC – is it of importance and can it be made simple? Intensive Care Med 1993; 19: 365–366.Google Scholar
  2. 2.
    Mitchell RR, Ross MW, Holzapfel L, Benis AM, Sierra D, Osborn JJ. Oxygen wash-in for monitoring functional residual capacity. Crit. Care Med 1982; 10(8): 529–533.Google Scholar
  3. 3.
    Jonmarker C, Jansson L, Jonson B, Larsson A, Werner O. Measurement of functional capacity by sulfur hexafluoride washout. Anesthesiology 1985; 63: 89–95.Google Scholar
  4. 4.
    Larsson A, Linnarson D, Jonmaker C, Jonson B, Larsson H, Werner O. Measurement of lung volume by sulfur hexafluoride washout during spontaneous and controlled Ventilation: Further development of a method. Anesthesiology 1987; 67: 543–550.Google Scholar
  5. 5.
    Zinserling J, Wrigge H, Varelmann D, Hering R, Putensen C. Measurement of functional residual capacity by nitrogen washout during partial ventilatory support. Intensive Care Med 2003; 29(5): 720–726.Google Scholar
  6. 6.
    Fretschner R, Deusch H, Weitnauer A, Brunner JX. A simple method to estimate functional residual capacity in mechanically ventilated patients. Intensive Care Med 1993; 19: 372–376.Google Scholar
  7. 7.
    Eichler W, Schumacher J, Roth-Isigkeit A, Braun J, Kuppe H, Klotz KF. Automated evaluation of functional residual capacity by oxygen washout. J Clin Monit Comput 2002; 17(3–4): 195–201.Google Scholar
  8. 8.
    Brunner JX, Wolff G, Cumming G, Langenstein H. Accurate measurement of N2 volume during N2 washout requires dynamic adjustment of delay time. J Appl Physiol 1985; 59(3): 1008–1012.Google Scholar
  9. 9.
    Ibanez J, Raurich JM, Moris SG. Measurement of functional residual capacity during mechanical ventilation. Comparison of a computerized open nitrogen washout method with a closed helium dilution method. Int Care Med 1983; 9: 91–93.Google Scholar
  10. 10.
    Snow M. Determination of functional residual capacity. Respiratory Care 1989; 34(7): 586–596.Google Scholar
  11. 11.
    Farmery AD, Hahn CEW. A method of reconstruction of clinical gas-analyzer signals corrupted by positive-pressure ventilation. J. Appl. Physiol 2001; 90: 1282–1290.Google Scholar
  12. 12.
    Lundin G. Nitrogen elimination during oxygen breathing. Acta Physiol Scand Suppl 1953; 111: 130–143.Google Scholar

Copyright information

© Springer Science + Business Media, Inc. 2006

Authors and Affiliations

  • Dieter Weismann
    • 1
  • Hajo Reißmann
    • 2
  • Stefan Maisch
    • 2
  • Bernd Füllekrug
    • 2
  • Jochen Schulte
    • 2
  1. 1.Drägerwerk AGLübeckGermany
  2. 2.Klinik und Poliklinik für AnästhesiologieUniversitätsklinikum Hamburg-EppendorfHamburgGermany

Personalised recommendations