Abstract
BACKGROUND: Volumetric capnography is an alternative method of measuring expired carbon dioxide partial pressure (PeCO2) and physiologic dead-space-to-tidal-volume ratio (VD/VT) during mechanical ventilation. In this method, PeCO2 is measured at the Y-adapter of the ventilator circuit, thus eliminating the effects of compression volume contamination and the need to apply a correction factor. We investigated the accuracy of volumetric capnography in measuring VD/VT, compared to both uncorrected and corrected measurements, using a metabolic monitor in patients with acute respiratory distress syndrome (ARDS).
METHODS: There were 90 measurements of VD/VT made in 23 patients with ARDS. The PeCO2 was measured during a 5-min expired-gas collection period with a Delta-trac metabolic monitor, and was corrected for compression volume contamination using a standard formula. Simultaneous measurements of PeCO2 and VD/VT were obtained using volumetric capnography.
RESULTS: VD/VT measured by volumetric capnography was strongly correlated with both the uncorrected (r2 = 0.93, p < 0.0001) and corrected (r2 = 0.89, p < 0.0001) measurements of VD/VT made using the metabolic monitor technique. Measurements of VD/VT made with volumetric capnography had a bias of 0.02 and a precision of 0.05 when compared to the VD/VT corrected for estimated compression volume contamination.
CONCLUSION: Volumetric capnography measurements of VD/VT in mechanically-ventilated patients with ARDS are as accurate as those obtained by metabolic monitor technique.
- acute respiratory distress syndrome
- dead-space fraction
- dead-space-to-tidal volume ratio
- volumetric capnography
- metabolic
- monitor
Footnotes
- Correspondence: Richard H Kallet MSc RRT FAARC, Respiratory Care Services, San Francisco General Hospital, NH: GA–2, 1001 Potrero Avenue, San Francisco CA 94110. E-mail: richkallet{at}earthlink.net.
- Copyright © 2005 by Daedalus Enterprises Inc.
