Abstract
BACKGROUND:
We tested the association between pulmonary dead-space fraction (ratio of dead space to tidal volume [VD/VT]) and mortality in subjects with ARDS (Berlin definition, PaO2 /FIO2 ≤ 300 mm Hg; PEEP ≥ 5 cm H2O) enrolled into a clinical trial incorporating lung-protective ventilation.
METHODS:
We conducted a prospective, multi-center study at medical-surgical ICUs in the United States. A total of 126 ALI subjects with acute lung injury were enrolled into a phase 3 randomized, placebo-controlled study of aerosolized albuterol. VD/VT and pulmonary mechanics were measured within 4 h of enrollment and repeated daily on study days 1 and 2 in subjects requiring arterial blood gases for clinical management.
RESULTS:
At baseline, non-survivors had a trend toward higher VD/VT compared with survivors (0.62 ± 0.11 vs 0.56 ± 0.11, respectively, P = .08). Differences in VD/VT between non-survivors and survivors became significant on study days 1 (0.64 ± 0.12 vs 0.55 ± 0.11, respectively, P = .01) and 2 (0.67 ± 0.12 vs 0.56 ± 0.11, respectively, P = .004). Likewise, the association between VD/VT and mortality was significant on study day 1 (odds ratio per 0.10 change in VD/VT [95% CI]: 6.84 [1.62–28.84] P = .01; and study day 2: 4.90 [1.28–18.73] P = .02) after adjusting for VD/VT, PaO2 /FIO2 , oxygenation index, vasopressor use, and the primary risk for ARDS. Using a Cox proportional hazard model, VD/VT was associated with a trend toward higher mortality (HR = 4.37 [CI 0.99–19.32], P = .052) that became significant when the analysis was adjusted for daily oxygenation index (HR = 1.74 [95% CI 1.12–3.35] P = .04).
CONCLUSIONS:
Markedly elevated VD/VT (≥ 0.60) in early ARDS is associated with higher mortality. Measuring VD/VT may be useful in identifying ARDS patients at increased risk of death who are enrolled into a therapeutic trial.
Keywords
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