Diagnosis: Bilateral lung infiltrates on chest X-ray, no history of chronic lung disease, or clinical suspicion of left heart failure (i.e., pulmonary artery occlusion pressure <18 mmHg, when available), and a PaO2 to inspired O2 fraction (FiO2) ratio being less than 200 with the following initial ventilatory settings: pressure-controlled ventilation (PCV, Servo 900C or Servo 300, Stemens-Elema, Sweeden), tidal volume of 10 ml/kg, respiratory rate of 15, inspiratory to expiratory time ratio of 1/2, FiO2 of 1.0 and PEEP of 5 cm H2O.
Management: All patients are paralyzed with vecuronium (0.1 mg.kg-1.h-1) and sedated with midazolam (0.3 mg/kg/h). Radial artery was catheterized for monitoring arterial pressure (Viggo-Spectramed, USA), and blood sampling for blood gas analyses (ABL-500, Radiometer, Copenhagen, Denmark). PEEP titration was applied at 3 cm H2O increments until reaching 15 cm H2O. Our major aim was to keep PaO2 between 60 and 100 mmHg. Accordingly, FiO2 was manipulated to maintain PaO2 greater than 60 mmHg. Peak pressure was not permitted to increase more than 40 cm H2O. Blood gas analyses and gas exchange parameters were recorded at each PEEP level after a stabilization period of 20-30 minutes. The PEEP value which maintained the best oxygenation with the least hemodynamic effect was accepted.
Weaning: As clinical improvement permitted, the following parameters were gradually decreased in the following order: FiO2, peak airway pressure, and then PEEP. Patients were accepted into the weaning program when they were clinically and hemodynamically stable with FiO2 < 0.5, PEEP of ≤ 5 cm H2O, an arterial oxygen saturation of > 90%, and a maximal inspiratory pressure < -25 cm H2O. Pressure support ventilation (PSV) and CPAP were used in the early phase of weaning. Subsequently, we used procedures including high-flow oxygen through an open circuit (T-piece, high flow) and low-flow of oxygen model (easy-breath, humidifier). Mechanical ventilation was thus avoided in the late weaning phases.
Airway Management: Percutaneous dilatational tracheostomy was performed for patients who required prolonged mechanical ventilation.
Position: Patients were maintained in semi-recumbent (≥ 30º) position unless a diagnosis of ARDS had been made. In those patients, prone positioning was used routinely. We used prone position, because a previous study from our unit demonstrated that this position improved respiratory parameters without provoking adverse hemodynamic consequences.
Enteral nutrition: Early enteral nutrition was encouraged. Maximum nutritional intake was set at 2500 kcal/day to avoid excessive CO2 production.
Hemodynamic management: In general, MAP was maintained above 60 mmHg. For this purpose, the order of management was as follows: 1) crystalloids, and then colloids, were given at a rate sufficient to keep pulmonary-artery occlusion pressure in between 9 and 18 mmHg; and, 2) hemoglobin was maintained above 10 g/dL (unless clinically contrindicated).
Prevention of Hospital Infections