부산대학교 도서관

This thesis is organized as a compendium of publications. It includes three original studies and a review paper. All of these papers follow the same line of clinical research. Such research analyzed different therapeutic strategies in patients with severe acute respiratory failure during invasive mechanical ventilation. Specifically, we mainly focused on three aspects. First we studied the acute physiological effects of lung recruitment maneuvers (RM) performed at high airway pressures in patients with acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). Second, we evaluated the effects on respiratory mechanics and gas exchange of the use of different humidification devices in ALI and ARDS. Third, we compared the effects of these different types of humidification on the airflow resistance of the endotracheal tube and the consequent increased work of breathing during withdrawal of mechanical ventilation. The main results observed were: - The use of RM performed at high airway pressures may improve oxygenation of patients in early stage of ALI and ARDS. However, it may worsen respiratory mechanics in some. The response is heterogeneous and is unpredictable (in terms of plateau pressures and lung compliance). In addition, the RM procedure can cause significant hemodynamic instability. The use of ventilatory parameters that combine moderate levels of tidal volume and positive end-expiratory makes unnecessary the routine use of these maneuvers. - The change of a passive humidification device to an active humidification system is a simple and useful strategy to reduce the instrumental dead space and, consequently, the levels of arterial carbon dioxide. This effect allowed to decrease the tidal volume, with the consequent decrease in driving pressures. The analysis of changes in respiratory mechanics after instrumental dead space and tidal volume reduction strongly suggest a decrease in alveolar overdistension. - The increase in airflow resistance of the endotracheal tube caused by the adhesion of respiratory secretions adhesion during routine mechanical ventilation showed no difference between active and passive humidification devices. The increase in resistances, however, may be clinically relevant during the weaning phase of mechanical ventilation. All these results have provided relevant clinical data for the understanding of the pathophysiology of acute respiratory failure in patients undergoing mechanical ventilation. Furthermore, our results can be extrapolated to the routine practice of mechanical ventilation in every intensive care department.