A new ventilation inhomogeneity index from multiple breath indicator gas washout tests in mechanically ventilated patients

Crit Care Med. 1993 Aug;21(8):1149-58. doi: 10.1097/00003246-199308000-00013.


Objectives: a) To determine the validity of a new method to analyze indicator gas washout tests on mechanically ventilated patients. This method takes into account the difference between the end-expiratory gas fraction and the mean gas fraction in the lung and provides the end-expiratory lung volume and a new index of ventilation inhomogeneity called volumes regression index. b) To determine the validity of this index as a predictor of chronic obstructive pulmonary disease. c) To compare this index with the moment ratio index and Becklake index.

Design: Prospective study of diagnostic test. Criterium standards: Closed-circuit indicator gas dilution technique and Tiffeneau index.

Setting: Surgical intensive care unit of a university hospital.

Patients: A total of 38 mechanically ventilated postoperative patients, divided into two groups: the obstructive group (n = 21) and the nonobstructive group (n = 17), based on their preoperative lung function.

Interventions: None.

Measurements and main results: a) The mean coefficient of variation of all lung volume measurements in a group of nine healthy volunteers was 5%, and the difference between this technique and the closed-circuit helium dilution measurements was -2 +/- 5%. In patients, the mean coefficient of variation of the lung volume measurements was 3.5%. The volumes regression index was measured as 0.02 +/- 0.04 in a dummy lung, 0.37 +/- 0.08 in the healthy volunteers, 0.64 +/- 0.23 in the nonobstructive patients, and 1.1 +/- 0.3 in the obstructive patients. The volumes regression index provided a better correlation (r2 = .46) with preoperatively determined Tiffeneau index than the Becklake index (r2 = .11) or the moment ratio index (r2 = .18).

Conclusion: The proposed technique provides a means for accurate measurement of the end-expiratory lung volume and the amount of ventilation inhomogeneity in mechanically ventilated intensive care unit patients.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Body Height
  • Breath Tests / instrumentation
  • Breath Tests / methods*
  • Female
  • Helium
  • Humans
  • Lung Diseases, Obstructive / diagnosis*
  • Lung Diseases, Obstructive / epidemiology
  • Lung Diseases, Obstructive / physiopathology
  • Lung Diseases, Obstructive / therapy
  • Lung Volume Measurements / instrumentation
  • Lung Volume Measurements / methods*
  • Male
  • Mass Spectrometry
  • Middle Aged
  • Prospective Studies
  • Pulmonary Gas Exchange*
  • Reproducibility of Results
  • Respiration, Artificial*
  • Sensitivity and Specificity
  • Severity of Illness Index
  • Vital Capacity


  • Helium