The Science Journal of the American Association for Respiratory Care

2003 OPEN FORUM Abstracts

Sustained Elevation in Pulmonary Dead-Space-to-Tidal Volume Ratio (VD/VT) Characterizes Non-survivors with Acute Respiratory Distress Syndrome

RH Kallet, JA Alonso, JF Pittet, TJ Nuckton, BM Daniel, MD Eisner and MA Matthay. Cardiovascular Research Institute, University of California San Francisco,.

Introduction: We previously reported that VD/VT was elevated early in acute respiratory distress syndrome (ARDS) and higher VD/VT levels were associated with increased mortality (NEJM 346:128;2002). We have now investigated whether elevated VD/VT is a consistent characteristic of non-survivors over the first 6 days of ARDS. 

Methods:
 VD/VT was measured in 59 patients within 24 h of meeting American-European Consensus Conference criteria for ARDS and repeated on days 2,3 and 6. VD/VT was measured using a bedside metabolic monitor and corrected for compression volume. Patients were ventilated at approximately 10 mL/kg. Data were analyzed by one-way ANOVA and Tukey-Kramer multiple comparison test. Paired comparisons were made with the Mann-Whitney test. Alpha was set at 0.05. 

RESULTS:
 VD/VT was significantly elevated when non-survivors were compared to survivors on each day. Nonsurvivors were characterized by a mean VD/VT that was > 0.60 and tended to increase as the disease progressed to the subacute phase. In contrast, survivors had mean VD/VT < 0.55 throughout the first week of ARDS. Approximately 25% (7/29) of survivors had an initial VD/VT of 0.67 ± 0.05 that trended down to 0.61 ± 0.07 by Day 6. Likewise, in 7/30 nonsurvivors the initial VD/VT was 0.51 ± 0.04 but had increased to 0.63 ± 0.10 (p=0.035) by Day 6.




CONCLUSION:
 The markedly elevated VD/VT that characterizes nonsurvivors is sustained beyond the early phase of ARDS. Our results suggest that measuring VD/VT beyond the first day of ARDS may provide useful prognostic information. Supported by NIH R01HL 51856

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