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Objective:
To compare 13 commercially available, new-generation, intensive-care-unit (ICU) ventilators in terms of trigger function, pressurization capacity during pressure-support ventilation (PSV), accuracy of pressure measurements, and expiratory resistance.
Design and Setting:
Bench study at a research laboratory in a university hospital.
Methods:
Four turbine-based ventilators and nine conventional servo-valve compressed-gas ventilators were tested using a two-compartment lung model. Three levels of effort were simulated. Each ventilator was evaluated at four PSV levels (5, 10, 15, and 20cm H2O), with and without positive end-expiratory pressure (5cm H2O). Trigger function was assessed as the time from effort onset to detectable pressurization. Pressurization capacity was evaluated using the airway pressure–time product computed as the net area under the pressure–time curve over the first 0.3s after inspiratory effort onset. Expiratory resistance was evaluated by measuring trapped volume in controlled ventilation.
Results:
Significant differences were found across the ventilators, with a range of triggering delays from 42 to 88 ms for all conditions averaged (P<0.001). Under difficult conditions, the triggering delay was longer than 100ms and the pressurization was poor for five ventilators at PSV5 and three at PSV10, suggesting an inability to unload patient's effort. On average, turbine-based ventilators performed better than conventional ventilators, which showed no improvement compared to a bench comparison in 2000.
Conclusion:
Technical performance of trigger function, pressurization capacity, and expiratory resistance differs considerably across new-generation ICU ventilators. ICU ventilators seem to have reached a technical ceiling in recent years, and some ventilators still perform inadequately (Figs 1, 4 and 6).
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Figure 1: a Evaluation of trigger performance. Pressure signal showing the inspiratory delay (DI), which is the sum of the triggering delay (DT) from the beginning of the simulated patient effort to the beginning of ventilator pressurization and the pressurization delay (DP) from the maximum airway pressure drop (ΔP) to the return to baseline pressure. b Evaluation of pressurization capacity. Pressure signal showing the pressurization capacity represented by the positive area over the first 0.3s of the simulated patient effort (hatched area). The red signal illustrates poor pressurization capacity: the time needed to reach the set pressure is longer and the positive area is smaller. (Reprinted from Thille AW, Lyazidi A, Richard J-CM, et al. A bench study of intensive-care-unit ventilators: new versus old and turbine-based versus compressed gas-based ventilators. Intensive Care Med. 2009;35:1368-1376, with kind permission from Springer Science+Business Media.)
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Figure 4: True delivered pressure support at different levels of pressure support. Each ventilator was tested for preset pressure supports of 5, 10, 15, and 20cm H2O. (Reprinted from Thille AW, Lyazidi A, Richard J-CM, et al. A bench study of intensive-care-unit ventilators: new versus old and turbine-based versus compressed gas-based ventilators. Intensive Care Med. 2009;35:1368-1376, with kind permission from Springer Science+Business Media.)
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Figure 6: Comparison of the nine compressed-gas ventilators (black squares) and the four turbine-based ventilators (white squares) regarding trigger performance assessed in terms of triggering delay and pressurization capacity assessed as the pressure–time product (PTP) over the first 0.3s after the start of the simulated effort. Trigger performance and pressurization capacity were significantly better with the turbine-based ventilators. (Reprinted from Thille AW, Lyazidi A, Richard J-CM, et al. A bench study of intensive-care-unit ventilators: new versus old and turbine-based versus compressed gas-based ventilators. Intensive Care Med. 2009;35:1368-1376, with kind permission from Springer Science+Business Media.)
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