Changes in occlusion pressure (P-0.1) and breathing pattern during pressure support ventilation

Background-The purpose of this study was to investigate changes in breathin g pattern, neuromuscular drive (P-0.1), and activity of the sternocleidomas toid muscles (SCM) during a gradual reduction in pressure support ventilati on (PSV) in patients being weaned off controlled mechanical ventilation. Methods-Eight non-COPD patients recovering from acute respiratory failure w ere included in this prospective interventional study. All patients were un able to tolerate discontinuation from mechanical ventilation. Each patient was evaluated during a period of spontaneous breathing and during PSV. Four successive levels of PSV were assessed in the following order: 20 cm H2O ( PS20), 15 cm H2O (PS15), 10 cm H2O (PS10), and 5 cm H2O (PS5). Results-When pressure support was reduced from PS20 to PS10 the respiratory rate (f) and the rapid shallow breathing index (f/VT) significantly increa sed and tidal volume (VT) significantly decreased. These parameters did not vary when pressure support was reduced from PS10 to PS5. Conversely, P-0.1 varied negligibly between PS20 and PS15 but increased significantly at low PSV levels. P-0.1 values were always greater than 2.9 cm H2O (4.1 (1.1) cm H2O) when SCM activity was present. When contraction of the SCM muscles re appeared the P-0.1 was the only parameter that changed significantly. Conclusions-in postoperative septic patients the value of P-0.1 seems to be more useful than breathing pattern parameters for setting the optimal leve l of pressure assistance during PSV.