The indications for mechanical ventilation (MV) include excessive work of breathing, with or without evidence of respiratory muscle fatigue. The setting of the MV is still a challenge because it is based on criteria understudied, often subjective and observer-dependent. Despite several studies, to our knowledge has never been done before is the precise definition of the optimal range of ventilatory support. Novel and recognizable diagnostic techniques will be applied. No single parameter of the breathing pattern has good accuracy for the adjustment of ventilatory support. Non-invasive measures such as P0.1 and rate of muscle relaxation may have good accuracy for the adjustment of ventilatory support.

Use of excessive pressure support

Inclusion Criteria:

• patients under invasive mechanical ventilation for 48h
• patients without the objective of complete rest of the respiratory muscles. This decision will be on the discretion of the attending physician,
• spontaneous breathing,
• clinically stability.

Exclusion Criteria:

• Previous disease of the central nervous system that can lead to respiratory changes.
• Previous disease of the peripheral nervous system that can lead to respiratory changes
• Previous muscular disease.