Abstract
BACKGROUND: The ratio of pulmonary dead space to tidal volume (VD/VT) in acute respiratory distress syndrome (ARDS) is reported to be between 0.35 and 0.55. However, VD/VT has seldom been measured with consideration to the evolving pathophysiology of ARDS.
METHODS: We made serial VD/VT measurements with 59 patients who required mechanical ventilation for ≥ 6 days. We measured VD/VT within 24 h of the point at which the patient met the American-European Consensus Conference criteria for ARDS, and we repeated the VD/VT measurement on ARDS days 2, 3, and 6 with a bedside metabolic monitor during volume-regulated ventilation. We analyzed the changes in VD/VT over the 6-day period to determine whether VD/VT has a significant association with mortality.
RESULTS: VD/VT was significantly higher in nonsurvivors on day 1 (0.61 ± 0.09 vs 0.54 ± 0.08, p < 0.05), day 2 (0.63 ± 0.09 vs 0.53 ± 0.09, p < 0.001), day 3 (0.64 ± 0.09 vs 0.53 ± 0.09, p < 0.001), and day 6 (0.66 ± 0.09 vs 0.51 ± 0.08, p < 0.001).
CONCLUSION: In ARDS a sustained VD/VT elevation is characteristic of nonsurvivors, so dead-space measurements made beyond the first 24 hours may have prognostic value.
- acute respiratory distress syndrome
- respiratory dead space
- dead-space
- dead-space-to-tidal volume ratio
- expired carbon dioxide
- acute lung injury
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: rkallet{at}sfghsom.ucsf.edu.
- Copyright © 2004 by Daedalus Enterprises Inc.
