Numerous decisions need to be made once it is determined that a patient requires mechanical ventilation, including the mode of mechanical ventilation. The mode refers to the method of inspiratory support. Its selection is generally based on clinician familiarity and institutional preferences since there is a paucity of evidence indicating that the mode affects clinical outcome.
Common modes of mechanical ventilation are described in this topic review (table 1). Other aspects of initiating mechanical ventilation are discussed separately. (See "Overview of mechanical ventilation".)
Volume-limited ventilation (also called volume-controlled or volume-cycled ventilation) requires the clinician to set the peak flow rate, flow pattern, tidal volume, respiratory rate, positive end-expiratory pressure (applied PEEP), and fraction of inspired oxygen (FiO2). Inspiration ends after delivery of the set tidal volume.
The inspiratory time and inspiratory to expiratory (I:E) ratio are determined by the peak inspiratory flow rate. Increasing the peak inspiratory flow rate will decrease inspiratory time, increase expiratory time, and decrease the I:E ratio.
Airway pressures (peak, plateau, and mean) depend on both the ventilator settings and patient-related variables (eg, compliance, airway resistance). High airway pressures may be a consequence of large tidal volumes, a high peak flow, poor compliance (eg, acute respiratory distress syndrome, minimal sedation), or increased airway resistance (figure 1 and waveform 1).