Cycling-off modes during pressure support ventilation: effects on breathing pattern, patient effort, and comfort

Expiratory asynchrony during pressure support ventilation (PSV) has been recognized as a cause of patient discomfort, increased workload, and impaired weaning process. We evaluated breathing pattern, patient comfort, and patient effort during PSV comparing 2 flow termination criteria: fixed at 5% of peak inspiratory flow vs automatic, real-time, breath-by-breath adjustment within the range of 5% to 55%.

Randomized crossover clinical trial. Sixteen awake patients, in the process of weaning, under PSV for more than 24 hours were subjected to 3 phases of PSV, each lasting 1 hour and using 1 of the 2 aforementioned termination criteria.

Effective pressure support during automatic adjustment (AA) was 12.5±3.2 cm H2O vs 12.5±3.9 cm H2O (P=.9) with the fixed termination criterion, and external positive end-expiratory pressure was 6.2±1.8 vs 6.8±2 (P<.05). The effective termination criterion was higher during AA (31% [23-39] vs 12% [6-23]; P<.01), but without producing premature breath terminations. Pressure overshoots and alternative cycling-off were also decreased. Throughout the AA period, we observed a higher respiratory rate (24±8 breaths/min vs 19±6 breaths/min; P<.001), lower tidal volume (484 ± 88 mL vs 518±102 mL; P<.001), and shorter inspiratory times (1.0±0.3 seconds vs 1.3±0.3 seconds; P<.001). Automatic adjustment was associated with lower airway occlusion pressure after 0.1 second (P0.1) (1.8±0.9 cm H2O vs 2.4±1 cm H2O; P<.01), lower pressure-time product to trigger the ventilator, and lower subjective discomfort (visual analog scale, 3.7±1.3 vs 4.5±1.2; P<.001).

When compared with a fixed termination criterion, the use of a variable, real-time-adjusted termination criterion improved some indices of patient-ventilator synchrony, producing better breathing pattern, less discomfort, and slightly lower patient effort during PSV.