Some investigators have speculated that the results of trials that enrolled ALI/ARDS patients using the AECC criteria without a minimum PEEP level were confounded by imbalances between study groups in patients with mild and severe lung injury that could not be detected without increasing PEEP ( 10). ![]() If so, then use of the AECC criteria to identify patients for ALI/ARDS trials, without PEEP and FiO 2 criteria, could reduce the power of clinical trials because potential effects of new interventions may be smaller in patients with mild disease. Thus, without standardized or minimum PEEP and FiO 2 criteria, the AECC criteria could identify a heterogeneous group of patients, some of whom are at low risk of adverse outcomes such as death. This suggests that among patients with similar PaO 2/FiO 2s, oxygenation failure is worse and risk of death is higher in those receiving higher FiO 2s. Moreover, in many patients with bilateral infiltrates, PaO 2/FiO 2s increased substantially when FiO 2s were raised from moderate to high levels ( 11, 13). In one study the mortality of these patients was considerably lower than those whose PaO 2/FiO 2s remained below 200 after raising PEEP ( 10). In these patients, atelectasis could have been an important cause of hypoxemia rather than shunt from consolidation and pulmonary edema. ![]() In some patients with bilateral infiltrates, PaO 2/FiO 2s were lower than 200 while they received mechanical ventilation with zero or low levels of PEEP, but PaO 2/FiO 2s then increased to greater than 200 or even 300 when low to moderate levels of PEEP were subsequently applied ( 9- 12). Many clinical studies of ALI/ARDS have used the AECC criteria to identify potentially eligible patients ( 2- 8). ![]() The American-European consensus conference (AECC) criteria for acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) include the acute onset of: ( 1) bilateral infiltrates on frontal chest radiograph, ( 2) PaO 2/FiO 2 less than or equal to 300 Torr (ALI) or 200 Torr (ARDS), and ( 3) absence of clinical indicators of left atrial hypertension ( 1).
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