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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, resistance, 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., Results: 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 that peak negative esophageal pressure, central respiratory drive, duration of ARDS/ALI, minute ventilation deficit between mechanical ventilation and spontaneous breathing, and female gender were the strongest predictors of f/VT., Conclusion: The characteristic rapid shallow breathing pattern in patients with ARDS/ALI occurs in the context of markedly diminished compliance, elevated respiratory drive, and increased WOB. That f/VT had a strong, inverse relationship to peak negative esophageal pressure also may reflect the influence of muscle weakness.

Objective: To assess the effects of step-changes in tidal volume on work of breathing during lung-protective ventilation in patients with acute lung injury (ALI) or the acute respiratory distress syndrome (ARDS)., Design: Prospective, nonconsecutive patients with ALI/ARDS., Setting: Adult surgical, trauma, and medical intensive care units at a major inner-city, university-affiliated hospital., Patients: Ten patients with ALI/ARDS managed clinically with lung-protective ventilation., Interventions: Five patients were ventilated at a progressively smaller tidal volume in 1 mL/kg steps between 8 and 5 mL/kg; five other patients were ventilated at a progressively larger tidal volume from 5 to 8 mL/kg. The volume mode was used with a flow rate of 75 L/min. Minute ventilation was maintained constant at each tidal volume setting. Afterward, patients were placed on continuous positive airway pressure for 1-2 mins to measure their spontaneous tidal volume., Measurements and Main Results: Work of breathing and other variables were measured with a pulmonary mechanics monitor (Bicore CP-100). Work of breathing progressively increased (0.86 +/- 0.32, 1.05 +/- 0.40, 1.22 +/- 0.36, and 1.57 +/- 0.43 J/L) at a tidal volume of 8, 7, 6, and 5 mL/kg, respectively. In nine of ten patients there was a strong negative correlation between work of breathing and the ventilator-to-patient tidal volume difference (R = -.75 to -.998)., Conclusions: : The ventilator-delivered tidal volume exerts an independent influence on work of breathing during lung-protective ventilation in patients with ALI/ARDS. Patient work of breathing is inversely related to the difference between the ventilator-delivered tidal volume and patient-generated tidal volume during a brief trial of unassisted breathing.

Background: Pressure-control ventilation (PCV) and pressure-regulated volume-control (PRVC) ventilation are used during lung-protective ventilation because the high, variable, peak inspiratory flow rate (V (I)) may reduce patient work of breathing (WOB) more than the fixed V (I) of volume-control ventilation (VCV). Patient-triggered breaths during PCV and PRVC may result in excessive tidal volume (V(T)) delivery unless the inspiratory pressure is reduced, which in turn may decrease the peak V (I). We tested whether PCV and PRVC reduce WOB better than VCV with a high, fixed peak V (I) (75 L/min) while also maintaining a low V(T) target., Methods: Fourteen nonconsecutive patients with acute lung injury or acute respiratory distress syndrome were studied prospectively, using a random presentation of ventilator modes in a crossover, repeated-measures design. A target V(T) of 6.4 + 0.5 mL/kg was set during VCV and PRVC. During PCV the inspiratory pressure was set to achieve the same V(T). WOB and other variables were measured with a pulmonary mechanics monitor (Bicore CP-100)., Results: There was a nonsignificant trend toward higher WOB (in J/L) during PCV (1.27 + 0.58 J/L) and PRVC (1.35 + 0.60 J/L), compared to VCV (1.09 + 0.59 J/L). While mean V(T) was not statistically different between modes, in 40% of patients, V(T) markedly exceeded the lung-protective ventilation target during PRVC and PCV., Conclusions: During lung-protective ventilation, PCV and PRVC offer no advantage in reducing WOB, compared to VCV with a high flow rate, and in some patients did not allow control of V(T) to be as precise.

Objective: To assess the impact of implementing a low tidal volume ventilation strategy on hospital mortality for patients with acute lung injury or acute respiratory distress syndrome., Design: Retrospective, uncontrolled study., Setting: Adult medical-surgical and trauma intensive care units at a major inner city, university-affiliated hospital., Patients: A total of 292 patients with acute lung injury or acute respiratory distress syndrome., Interventions: Between the years 2000 and 2003, 200 prospectively identified patients with acute lung injury/acute respiratory distress syndrome were managed by the ARDS Network low tidal volume protocol. A historical control group of 92 acute respiratory distress syndrome patients managed by routine practice from 1998 to 1999 was used for comparison., Measurements and Main Results: Patients managed with the ARDS Network protocol had a lower hospital mortality compared with historical controls (32% vs. 51%, respectively; p = .004). Multivariate logistic regression estimated an odds ratio of 0.32 (95% CI, 0.17-0.59; p = .0003) for mortality risk with use of the ARDS Network protocol. Protocol-managed patients had a lower tidal volume (6.2 +/- 1.1 vs. 9.8 +/- 1.5 mL/kg; p < .0001) and plateau pressure (27.5 +/- 6.4 vs. 33.8 +/- 8.9 cm H2O; p < .0001) than historical controls., Conclusion: Adoption of the ARDS Network protocol for routine ventilator management of acute lung injury/acute respiratory distress syndrome patients was associated with a lower mortality compared with recent historical controls.

Background: The international consensus definitions for acute respiratory distress syndrome (ARDS) have formed the basis for recruitment into randomized, controlled trials and, more recently, standardized the protocols for ventilatory treatment of acute lung injury. Although possibly appropriate for sepsis-induced ARDS, these criteria may not be appropriate for posttraumatic ARDS if the disease patterns are widely divergent. This study tests the hypothesis that standard ARDS criteria applied to the trauma population will capture widely disparate forms of acute lung injury and are too nonspecific to identify a population at risk for prolonged respiratory failure and associated complications., Methods: Patients with and Injury Severity Score > or = 16 ventilated for > 12 hours were prospectively enrolled. Clinical data, including elements of cardiovascular, renal, hepatic, hematologic, neurologic, and pulmonary function, were collected daily. Two hundred fifty-four patients were enrolled over a 36-month period, of whom 70 met the consensus definitions of ARDS. Patients from whom support was withdrawn within 48 hours were excluded. The remaining 61 patients were stratified into two groups on the basis of intubation (n = 12) days., Results: There was considerable disparity in severity and clinical course. A mild, limited form of ARDS was characterized by earlier onset (group 1, 2 days; group 2, 4 days; p = 0.002), fewer intubation days (7 days vs. 28 days; p < 0.001), and less severe derangements in lung mechanics. A significant difference between the two groups was also seen in systemic inflammatory response syndrome score, incidence of sepsis, and incidence of multiple organ failure., Conclusion: The criteria for ARDS, when applied to the trauma population, capture a widely disparate group and has poor specificity for identifying patients at risk. Recruitment of trauma patients for ARDS studies or preemptive ventilatory management based solely on these criteria may be ill-advised.

Objective: The purpose of this study was to determine the incidence of acute lung injury (ALI) in trauma patients with severe traumatic brain injury (TBI), to evaluate the impact of ALI on mortality and neurologic outcome after severe traumatic brain injury (TBI), and to identify whether the development of ALI correlates with the severity of TBI., Methods: Clinical data were collected prospectively over a 4-year period in a Level I trauma center. Patients included in the study met the following criteria: mechanical ventilation > 24 hours, head Abbreviated Injury Scale score >or= 3, no other body region Abbreviated Injury Scale score >or= 3, and age between 18 and 54 years. ALI was defined using international consensus criteria. Glasgow Outcome Scale scores were assessed at 3 and 12 months. Bivariate comparisons were made between ALI and non-ALI groups. Multivariate analysis with stepwise logistical regression was used to assess independent factors on mortality. The patient's admission head computed tomographic (CT) scan was graded using the Marshall system, and the presence and size of specific intracranial abnormality was noted. Glasgow Coma Scale (GCS) score, Marshall CT scan score, and intracranial abnormality were correlated with the development of ALI., Results: One hundred thirty-seven patients with isolated head trauma were enrolled in the study over a 4-year period. Thirty-one percent of patients with severe TBI developed ALI. Head trauma patients with ALI had a significantly higher ISS, a greater number of days on the ventilator, and a worse neurologic outcome for those who survived their hospitalization. Mortality was 38% in the ALI group and 15% in the non-ALI group (p = 0.004). Only 3 of 16 (19%) of the deaths within the ALI group were directly related to ALI. By multivariate analysis, only the presence of ALI, older age, and lower initial GCS score were associated with higher mortality. There was no association between ISS, the presence of arterial hypotension (arterial systolic pressure < 90 mm Hg) at admission to the hospital, or the amount of blood transfused and mortality. No correlation was found between the severity of head injury (GCS score, Marshall score, or intracranial abnormality) and development of ALI., Conclusion: The development of ALI is a critical independent factor affecting mortality in patients suffering traumatic brain injury and is associated with a worse long-term neurologic outcome in survivors. The risk of developing ALI is not associated with specific anatomic lesions diagnosed by cranial CT scanning.