Original Contributions The Spontaneous Breathing Pattern and Work of Breathing of Patients With Acute Respiratory Distress Syndrome and Acute Lung Injury

BACKGROUND: The spontaneous breathing pattern and its relationship to compliance, resistance, and work of breathing (WOB) has not been examined in patients with acute respiratory distress syndrome (ARDS) or acute lung injury (ALI). Clinically, the ratio of respiratory frequency to tidal volume (f/VT) during spontaneous breathing may reflect adaptation to altered compliance, resis-tance, and increased WOB. We examined the relationship between f/VT, WOB, and respiratory system mechanics in patients with ARDS/ALI. METHODS: Data from spontaneous breathing trials were collected from 33 patients (20 with ARDS, 13 with ALI) at various points in their disease course. WOB and respiratory system mechanics were measured with a pulmonary mechanics monitor that incorporates Campbell diagram software. Differences between the patients with ARDS and ALI were assessed with 2-sided unpaired t tests. Multivariate linear regression models were constructed to assess the relationship between f/VT and other pulmonary-related variables. RE-SULTS: Patients with ARDS had significantly lower compliance than those with ALI (24 6 mL/ cm H2O vs 40 13 mL/cm H2O, respectively, p < 0.001), but this did not translate into significant differences in either WOB (1.70 0.59 J/L vs 1.43 0.90 J/L, respectively, p 0.30) or f/VT (137 82 vs 107 49, respectively, p 0.23). Multivariate linear regression modeling revealed tha