Volume-cycled decelerating flow; An alternative form of mechanical ventilation

The linearly decelerating flow waveform for volume-cycled mechanical ventilation is an option on many modern ventilators. We have developed mathematical models for two available forms of volume-cycled decelerating- flow ventilation (VCDF). These equations use clinician-chosen ventilator settings as inputs (frequency, tidal volume, peak inspiratory flow or inspiratory time fraction, and end-inspiratory pause), and patient-determined inputs which describe the patient's ventilatory impedance (inspiratory [RI] and expiratory [RE] resistance and respiratory system compliance [C]. The equations predict key outcome variables: mean airway pressure; and peak, mean, and end-expiratory alveolar pressures. The mathematical expressions were validated in a mechanical lung analog. Values observed in the test lung were compared to values predicted by the mathematical models for a wide range of ventilator settings and impedance combinations (RI and RE, 5 to 40 cm H₂O·s/L; C, 0.02 to 0.10 L/cm H₂O). The correspondence between observed and predicted values was generally excellent across the broad range of inputs tested (r≥0.98). Outcome variables were quite sensitive to clinician-chosen inputs over certain critical ranges. Carefully applied, VCDF offers several theoretic advantages for the clinical setting; however, appropriate caution must be exercised to avoid the application of tissue-injuring pressure.