Inhalation proceeds until a set tidal volume (TV) is delivered and is followed by passive exhalation. A feature of this mode is that gas is delivered with a constant inspiratory flow pattern, resulting in peak pressures applied to the airways higher than that required for lung distension (plateau pressure). Since the volume delivered is constant, applied airway pressures vary with changing pulmonary compliance (plateau pressure) and airway resistance (peak pressure).
Because the volume-cycled mode ensures a constant minute ventilation despite potentially abnormal lung compliance, it is a common choice as an initial ventilatory mode in the ED. A major disadvantage is that high airway pressures may be generated, potentially resulting in barotrauma. Close monitoring and use of pressure limits are helpful in avoiding this problem. Note that portable ventilators set to volume-cycled mode function well as monitors of patients' pulmonary compliance, which will be decreased in physiological states such as worsening ARDS, pneumothorax, right mainstem intubation, chest-wall rigidity, increased intra-abdominal pressure, and psychomotor agitation ("fighting the vent"). These pathophysiological states increase peak pressure and should be considered whenever pressure alarms are sounded.