LUNG STRUCTURE AND FUNCTION IN DIFFERENT STAGES OF SEVERE ADULT-RESPIRATORY-DISTRESS-SYNDROME

Objective.-To assess the clinical consequences of duration of adult re spiratory distress syndrome (ARDS) on lung structure and function. Des ign.-Retrospective analysis. Setting.-A university hospital referral c enter for extracorporeal support. Patients.-A total of 84 patients wit h severe ARDS (Murray score > 2.5) recruited from 48 intensive care un its (1979 to 1992), who suffered ARDS and underwent mechanical ventila tion for up to 1 week (37 patients with early ARDS), between 1 and 2 w eeks (24 patients with intermediate ARDS), or more than 2 weeks (23 pa tients with late ARDS) and subsequently underwent extracorporeal suppo rt. Main Outcome Measures.-Before beginning extracorporeal support, we measured gas exchange, pulmonary mechanics, hemodynamics, oxygen tran sport and delivery, incidence of barotrauma (presence of one or more t horacic tubes for pneumothorax drainage), and organ dysfunctions. In a subgroup of 16 patients, we studied lung structure by computed tomogr aphic scan, scoring the densities and quantifying the emphysemalike le sions (bullae). Results.-Late ARDS showed lower respiratory compliance , higher dead space, higher Pace,, lower venous admixture, and lower p ositive end-expiratory pressure requirement compared with early ARDS ( P<.01). The incidence of pneumothorax (48.8% of the entire population) was significantly (P<.01) higher in late ARDS (87%) vs intermediate A RDS (46%) and early ARDS (30%). The mortality of patients with pneumot horax (66%) was significantly (P<.01) higher compared with patients wi thout pneumothorax (46%). The number of bullae per lung was significan tly higher in late ARDS vs intermediate and early ARDS (mean [SD], 8 [ 4], 4.3 [5], and 1.9 [3.9], respectively; P<.01), and they were prefer entially distributed in the dependent lung regions. The number of bull ae per lung was significantly higher in patients with pneumothorax vs those without pneumothorax (mean [SD], 13.6 [9.8] vs 1.4 [2.1]; P=.007 ). The mean (SD) duration of ARDS in patients with pneumothorax was 15 .3 (10.0) days vs 7.0 (6.6) days in those without pneumothorax (P=.000 1). No differences within the three groups were found in computed tomo graphic scan densities, hemodynamics, and number of organ system dysfu nctions. Conclusions.-The lung structure and function changes markedly with ARDS duration, and the late stages may be described as restricti ve lung disease with superimposed emphysemalike lesions. Presence of p neumothorax affects survival and appears to be related to the lung str uctural changes occurring with time.