HISTOLOGIC ASPECTS OF PULMONARY BAROTRAUMA IN CRITICALLY ILL PATIENTS WITH ACUTE RESPIRATORY-FAILURE

Objective: To describe histologically pulmonary barotrauma in mechanically ventilated patients with severe acute respiratory failure. Design: Assessment of histologic pulmonary barotrauma. Setting: A 14-bed surgical intensive care unit (SICU) Patients: The lungs of 30 young critically ill patients (mean age 34 +/- 10 years) were histologically examined in the immediate post-mortem period. None of them were suspected of pre-existing emphysema. Measurements and results: Clinical events and ventilatory settings used during mechanical ventilation were compared with lung histology. Airspace enlargement, defined as the presence of either alveolar overdistension in aerated lung areas or intraparenchymal pseudocysts in non-aerated lung areas, was found in 26 of the 30 lungs examined (86%). Patients with severe airspace enlargement (2.6 - 40 mm internal diameter) had a significantly greater incidence of pneumothorax (8 versus 2, p < 0.05), were ventilated using higher peak airway pressures (56 +/- 18 cmH2O versus 44 +/- 10 cmH2O, p < 0.05) and tidal volumes (12 +/- 3 ml/kg versus 9 +/- 2 ml/kg, p < 0.05), were exposed significantly longer to toxic levels of oxygen (8.6 +/- 9.4 days versus 1.9 +/- 2 days at FIO2 > 0.6, p < 0.05) and lost more weight (6.3 +/- 9.2 kg versus 0.75 +/- 5.8 kg, p < 0.05) than patients with mild airspace enlargement (1 - 2.5 mm internal diameter). Conclusion: Underlying histologic lesions responsible for clinical lung barotrauma consist of pleural cysts, bronchiolar dilatation, alveolar overdistension and intraparenchymal pseudocysts. Mechanical ventilation appears to be an aggravating factor, particularly when high peak airway pressures and large tidal volumes are delivered by the ventilator.