Effect of inspiratory synchronization during pressure-controlled ventilation on lung distension and inspiratory effort.

Background: In pressure-controlled (PC) ventilation, tidal volume (V ) and transpulmonary pressure (P ) result from the addition of ventilator pressure and the patient's inspiratory effort. PC modes can be classified into fully, partially, and non-synchronized modes, and the degree of synchronization may result in different V and P despite identical ventilator settings. This study assessed the effects of three PC modes on V , P , inspiratory effort (esophageal pressure-time product, PTP), and airway occlusion pressure, P . We also assessed whether P can be used for evaluating patient effort.

Methods: Prospective, randomized, crossover physiologic study performed in 14 spontaneously breathing mechanically ventilated patients recovering from acute respiratory failure (1 subsequently withdrew). PC modes were fully (PC-CMV), partially (PC-SIMV), and non-synchronized (PC-IMV using airway pressure release ventilation) and were applied randomly; driving pressure, inspiratory time, and set respiratory rate being similar for all modes. Airway, esophageal pressure, P , airflow, gas exchange, and hemodynamics were recorded.

Results: V was significantly lower during PC-IMV as compared with PC-SIMV and PC-CMV (387 ± 105 vs 458 ± 134 vs 482 ± 108 mL, respectively; p < 0.05). Maximal P was also significantly lower (13.3 ± 4.9 vs 15.3 ± 5.7 vs 15.5 ± 5.2 cmHO, respectively; p < 0.05), but PTP was significantly higher in PC-IMV (215.6 ± 154.3 vs 150.0 ± 102.4 vs 130.9 ± 101.8 cmHO × s × min, respectively; p < 0.05), with no differences in gas exchange and hemodynamic variables. PTP increased by more than 15% in 10 patients and by more than 50% in 5 patients. An increased P could identify high levels of PTP.

Conclusions: Non-synchronized PC mode lowers V and P in comparison with more synchronized modes in spontaneously breathing patients but can increase patient effort and may need specific adjustments. Clinical Trial Registration Clinicaltrial.gov # NCT02071277.