Risk stratification and closed-loop ventilation in critically ill patients

This thesis reports the results of three posthoc analyses on the prognostic value of variables related to oxygenation and ventilation in patients with ARDS, and the results of one non-inferiority randomized clinical trial on the quality of breathing during postoperative ventilation using closed-loop ventilation in patients after cardiac surgery. In the first part of this thesis we focused on the prognostic capacity of the ratio of the arterial oxygen tension (PaO₂) or peripheral oxygen saturation (SpO₂) to the fraction of inspired oxygen (FiO₂), i.e., PaO₂/FiO₂ or SpO₂/FiO₂, and the positive end–expiratory pressure for prognostication in mechanically ventilated patients with the acute respiratory distress syndrome at different time-points. Furthermore, we evaluated, whether changes in PaO₂/FiO₂, deadspace (V_D/V_T) and driving pressure (ΔP) induced by prone positioning could be used to predict mortality. In the second part we compared the quality of breathing during postoperative ventilation using two different sensor techniques for end–tidal CO₂ monitoring with INTELLiVENT–Adaptive Support Ventilation in cardiac surgery patients. We hypothesized that (1) SpO₂/FiO₂ could be used for risk stratification in patients with ARDS, and that the prognostic capacity would improve over time, (2) changes in PaO₂/FiO₂, V_D/V_T, and ΔP induced by prone positioning could be used for predicting mortality, and that (3) the quality of breathing using sidestream capnography is comparable to the quality of breathing using mainstream capnography with postoperative closed-loop ventilation in cardiac surgery patients.