Neural Pressure Support and Non-invasive Estimation of Transpulmonary Pressure in Spontaneous Ventilation Modes

The transition from controlled mechanical ventilation to assisted ventilation is one of the most complex and compromised phases of the ventilatory management during mechanical ventilation, affected by factors such as: * Asynchronies, due to patient-respirator dis-synchrony in ins- and expiratory neural and mechanical times, as well as inadequate levels of assistance. * Risks of self-induced lung injury resulting from uncontrolled increases in transpulmonary pressure when high inspiratory efforts are combined with inappropriate levels of inspiratory pressure assistance. Current monitoring of assisted ventilation is complex and not well resolved by most conventional ventilators. Asynchronies are difficult to monitor with the pressure or flow/time curves present in conventional ventilators requiring an advanced level of expertise. Measurements of the patient's muscular effort and therefore of transpulmonary pressure, requires the use of esophageal manometry with cumbersome handling and interpretation. NAVA (Neurally Adjusted Ventilatory Assist) is a ventilator mode that uses electrical activity of the diaphragm (EAdi), monitored via a modified nasogastric feeding catheter, to control and assist the respiratory cycle by the ventilator. Recently, a "hybrid" mode between the conventional pressure support assisted mode (PSV) and NAVA called Neural-Pressure Support Ventilation (N-PSV) has been developed. This mode uses a neural trigger based on the EAdi to match the patient's and ventilator's in- and expiratory time, but unlike NAVA, assisting in the same way as in pressure support. In addition the EAdi allows to assess the extent to which the patient's muscle strength contributes to the patient-ventilator breath (PVBC), and it has recently been suggested that on the basis of PVBC it may also be possible to directly estimate the patient's transpulmonary pressure (PL). Hypothesis: 1. EAdi allows direct estimation of PL during the assisted ventilation phase without the n