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

Objective: To describe histologically pulmonary barotrauma in mechanic ally ventilated patients with severe acute respiratory failure. Design : Assessment of histologic pulmonary barotrauma. Setting: A 14-bed sur gical intensive care unit (SICU) Patients: The lungs of 30 young criti cally ill patients (mean age 34 +/- 10 years) were histologically exam ined in the immediate post-mortem period. None of them were suspected of pre-existing emphysema. Measurements and results: Clinical events a nd ventilatory settings used during mechanical ventilation were compar ed with lung histology. Airspace enlargement, defined as the presence of either alveolar overdistension in aerated lung areas or intraparenc hymal 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 pn eumothorax (8 versus 2, p < 0.05), were ventilated using higher peak a irway 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 e xposed significantly longer to toxic levels of oxygen (8.6 +/- 9.4 day s 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 m ild airspace enlargement (1 - 2.5 mm internal diameter). Conclusion: U nderlying histologic lesions responsible for clinical lung barotrauma consist of pleural cysts, bronchiolar dilatation, alveolar overdistens ion and intraparenchymal pseudocysts. Mechanical ventilation appears t o be an aggravating factor, particularly when high peak airway pressur es and large tidal volumes are delivered by the ventilator.