In patients with acute respiratory distress syndrome (ARDS), mechanical ventilation is a life support therapy; however, its use is associated with ventilator-induced lung injury (VILI). VILI is the final manifestation of changes in lung mechanics that occurs in each ventilatory cycle in a damaged lung parenchyma. In each respiratory cycle, a certain amount of mechanical energy is transferred to the lung, which is used primarily to overcome airway resistance and expand the chest wall.This mechanical energy multiplied by the respiratory rate (RR) is what is known as mechanical power (MP), which reflects the amount of energy applied to the respiratory system per minute during mechanical ventilation (MV). The amount of energy transferred from the ventilator to the patient is measured in joules (J), while MP is defined as the amount of energy transferred per unit of time (J/minute). MP is a summary variable that includes: tidal volume (TV), RR, flow, positive end-expiratory pressure (PEEP) and driving pressure (difference between plateau pressure and PEEP). An experimental study showed that the increase in MP, through the increase in RR, was associated with VILI. There is also evidence that MP can predict the risk of mortality in mechanically ventilated patients with and without ARDS. In addition, a constant increase in the risk of death has been found with MP greater than 17.0 J/min. In turn, since this value could vary according to lung size, it has been proposed that MP normalized to lung size (assessed through lung compliance) may have better performance. One way to optimize the MP would be to limit the RR and TV. However, the decrease in any of these ventilatory variables can lead to inefficient ventilation and an increase in the arterial pressure of carbon dioxide (PaCO2). In recent years, the ventilatory ratio (VR) has been assessed. VR is a unitless ratio that it can be easily calculated using routine bedside variables. Its value reflects the ability of the lungs to excrete CO2 adequately. Higher values of VR were associated with higher pulmonary dead space and with mortality. In the ventilatory setting, the optimization of MP would lead to an increase in VR.In addition, and since the components of MP contribute unequally to its value, it would be important to be able to establish the variables that could be decisive in the ventilatory setting. For this reason, the primary outcome is to assess the relationship between PM and VR. The secondary outcomes are: to estimate the relationship between PM in relation to static compliance (PM/C) and VR, and to assess the differences in respiratory variables considering a MP of 17 J/min as cut-off point.
Mechanical power (MP) and ventilatory ratio (VR) are variables associated with outcomes in patients with acute respiratory distress syndrome (ARDS). In respiratory setting, the optimization of MP should lead to an increase in VR. Therefore, the objectives of this study are: to assess the relationship between MP and VR and to compare the components of MP (ventilatory variables) according to a level of MP (17 J/minute) considered harmful.