ventilação mecanica Flashcards
Trigger - the factor that initiates inspiration. A breath can be pressure-triggered, flow-triggered, or time-triggered.
Phases of Mechanical Breathing
-Initiation phase is the start of the mechanical breath, whether triggered by the patient or the machine. With a patient initiated breath, you will notice a slight negative deflection (negative pressure, or sucking).
-Inspiratory phase is the portion of mechanical breathing during which there is a flow of air into the patient’s lungs to achieve a maximal pressure, the peak airway pressure (PIP or Ppeak), and a tidal volume (TV or VT).
-Plateau phase does not routinely occur in mechanically ventilated breaths, but may be checked as an important diagnostic maneuver to assess the plateau pressure (Pplat). With cessation of air flow, the plateau pressure and the tidal volume (TV or VT) are briefly held constant.
-Exhalation is a passive process in mechanical breathing. The start of the exhalation process can be either volume cycled (when a maximum tidal volume is achieved), time cycled (after a set number of seconds), or flow cycled (after achieving a certain flow rate).
Ventilator Settings
Peak Inspiratory Pressure (PIP or Ppeak) is the maximum pressure in the airways at the end of the inspiratory phase.
Since this value is generated during a time of airflow, the PIP is a determined by both airway resistance and compliance. By convention, all pressures in mechanical ventilation are reported in “cm H2O.” It is best to target a PIP < 35 cm H2O.
Plateau Pressure (Pplat) is the pressure that remains in the alveoli during the plateau phase, during which there is a cessation of air flow, or with a breath-hold. To calculate this value, the clinician can push the “inspiratory hold” button on the ventilator. The plateau pressure is effectively the pressure at the alveoli with each mechanical breath, and reflects the compliance in the airways. To prevent lung injury, the Pplat should be maintained at < 30 cm H2O.
Driving pressure (∆P) is the term that describes the pressure changes that occurs during inspiration, and is equal to the difference between the plateau pressure and PEEP (Pplat – PEEP). For example, a patient with a Pplat of 30 cm H2O and a PEEP of 10 cm H20 would have a driving pressure of 20 cm H2O. In other words, 20 cm H2O would be the pressure that extered to expand the lungs.
