1/17/2024 0 Comments Cmh2o peep definitionTo characterize the relationship between baseline PEEP and FiO 2, we divided baseline FiO 2 into 10 subsets, each with FiO 2 range of 0.10, and then displayed distributions of PEEP within each interval. We created a frequency-distribution of baseline PEEP levels. Baseline values usually occurred several or many hours after the criteria for ALI were initially met. Baseline ventilator settings were set by clinicians and were available within 4 hours before the time of randomization. Etiologic causes of ALI/ARDS were listed as pneumonia (41%), sepsis (24%), aspiration (15%), trauma (9%), and other causes (11%). We reviewed existing data from 2,443 patients enrolled in 4 ARDS Network clinical trials from 1996 to 2005 ( 2- 5). Parts of this study were presented previously in abstracts ( 16, 17). To address this concern we examined effects of two study interventions on subsets of ALI/ARDS patients with mild and severe hypoxemia. A secondary purpose was to address the concern that in patients with mild disease, potential effects of an intervention may be small or nonexistent. The primary purpose of the present study was to explore the potential value of adding PEEP and FiO 2 criteria to the AECC criteria to exclude patients with low risk of mortality. Exclusion criteria reduced heterogeneity of the enrolled populations, but patients were not excluded if they were on zero or low PEEPs or low FiO 2s. The National Institutes of Health ARDS Network used the AECC criteria as the inclusion criteria for most of its clinical trials since 1996 ( 2- 5, 14, 15). 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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