Prevalence of Acute Lung Injury Among Medical Patients in the Emergency Department : ACUTE LUNG INJURY IN THE ED

In patients with the acute respiratory distress syndrome, massive alveolar collapse and cyclic lung reopening and overdistention during mechanical ventilation may perpetuate alveolar injury. We determined whether a ventilatory strategy designed to minimize such lung injuries could reduce not only pulmonary complications but also mortality at 28 days in patients with the acute respiratory distress syndrome. We randomly assigned 53 patients with early acute respiratory distress syndrome (including 28 described previously), all of whom were receiving identical hemodynamic and general support, to conventional or protective mechanical ventilation. Conventional ventilation was based on the strategy of maintaining the lowest positive end-expiratory pressure (PEEP) for acceptable oxygenation, with a tidal volume of 12 ml per kilogram of body weight and normal arterial carbon dioxide levels (35 to 38 mm Hg). Protective ventilation involved end-expiratory pressures above the lower inflection point on the static pressure-volume curve, a tidal volume of less than 6 ml per kilogram, driving pressures of less than 20 cm of water above the PEEP value, permissive hypercapnia, and preferential use of pressure-limited ventilatory modes. After 28 days, 11 of 29 patients (38 percent) in the protective-ventilation group had died, as compared with 17 of 24 (71 percent) in the conventional-ventilation group (P<0.001). The rates of weaning from mechanical ventilation were 66 percent in the protective-ventilation group and 29 percent in the conventional-ventilation group (P=0.005): the rates of clinical barotrauma were 7 percent and 42 percent, respectively (P=0.02), despite the use of higher PEEP and mean airway pressures in the protective-ventilation group. The difference in survival to hospital discharge was not significant; 13 of 29 patients (45 percent) in the protective-ventilation group died in the hospital, as compared with 17 of 24 in the conventional-ventilation group (71 percent, P=0.37). As compared with conventional ventilation, the protective strategy was associated with improved survival at 28 days, a higher rate of weaning from mechanical ventilation, and a lower rate of barotrauma in patients with the acute respiratory distress syndrome. Protective ventilation was not associated with a higher rate of survival to hospital discharge.

Although ventilation with small tidal volumes is recommended in patients with established acute lung injury, most others receive highly variable tidal volume aimed in part at normalizing arterial blood gas values. We tested the hypothesis that acute lung injury, which develops after the initiation of mechanical ventilation, is associated with known risk factors for ventilator-induced lung injury such as ventilation with large tidal volume. Retrospective cohort study. Four intensive care units in a tertiary referral center. Patients who received invasive mechanical ventilation for > or = 48 hrs between January and December 2001. None. The main outcome of interest, acute lung injury, was assessed by independent review of daily digital chest radiographs and arterial blood gases. Ventilator settings, hemodynamics, and acute lung injury risk factors were extracted from the Acute Physiology and Chronic Health Evaluation III database and the patients' medical records. Of 332 patients who did not have acute lung injury from the outset, 80 patients (24%) developed acute lung injury within the first 5 days of mechanical ventilation. When expressed per predicted body weight, women were ventilated with larger tidal volume than men (mean 11.4 vs. 10.4 mL/kg predicted body weight, p <.001) and tended to develop acute lung injury more often (29% vs. 20%, p =.068). In a multivariate analysis, the main risk factors associated with the development of acute lung injury were the use of large tidal volume (odds ratio 1.3 for each mL above 6 mL/kg predicted body weight, p <.001), transfusion of blood products (odds ratio, 3.0; p < 0.001), acidemia (pH < 7.35; odds ratio, 2.0; p =.032) and a history of restrictive lung disease (odds ratio, 3.6; p =.044). The association between the initial tidal volume and the development of acute lung injury suggests that ventilator-associated lung injury may be an important cause of this syndrome. Height and gender should be considered when setting up the ventilator. Strong consideration should be given to limiting large tidal volume, not only in patients with established acute lung injury but also in patients at risk for acute lung injury.

To further understanding of the epidemiology of acute respiratory distress syndrome (ARDS), we prospectively identified 695 patients admitted to our intensive care units from 1983 through 1985 meeting criteria for seven clinical risks, and followed them for development of ARDS and eventual outcome. ARDS occurred in 179 of the 695 patients (26%). The highest incidence of ARDS occurred in patients with sepsis syndrome (75 of 176; 43%) and those with multiple emergency transfusions (> or = 15 units in 24 h) (46 of 115; 40%). Of patients with multiple trauma, 69 of 271 (25%) developed ARDS. If any two clinical risks for trauma were present, the incidence of ARDS was 23 of 57, or 40%. During the study period, we identified 48 patients with ARDS who did not have one of the defined clinical risks, yielding a sensitivity of 79% (179 of 227). Secondary factors associated with increased risk for ARDS in clinical risk subgroups include an elevated Acute Physiologic and Chronic Health Evaluation II (APACHE II) score in patients with sepsis and increased APACHE II and Injury Severity Scores (ISS) in trauma victims. Mortality was threefold higher when ARDS was present (62%) than among patients with clinical risks who did not develop ARDS (19%; p < 0.05). The difference in mortality if ARDS developed was particularly striking in patients with trauma (56% versus 13%), but less in those with sepsis (69% versus 49%). The mortality data should be interpreted with caution, since the fatality rate in ARDS patients appears to have decreased in our institution from the time that these data were collected.(ABSTRACT TRUNCATED AT 250 WORDS)