The impact of the inspiratory-to-expiratory ratio on mechanical power in ARDS patients

Objective: Mechanical power (MP) is a promising parameter that may guide lung-protective ventilation strategies. The MP equation encompasses all variables involved in the pathogenesis of ventilator-induced lung injury (VILI), as well as the inspiratory-to-expiratory (I:E) ratio. Shortening the inspiratory time—by altering the I:E ratio—increases gas flow and may lead to lung injury. The optimal I:E ratio for preventing VILI remains uncertain. The present study aimed to investigate the effects of different I:E ratios on inspiratory gas flow and MP in patients with acute respiratory distress syndrome (ARDS). Materials and Methods: This study was conducted on 19 adult patients diagnosed with moderate ARDS who were admitted to the intensive care unit and received mechanical ventilation. Patients were ventilated at a PEEP level of 10 cmH2O, a tidal volume of 6 mL/kg, and three sequentially applied I:E ratios (1:2, 1:1, and 1.5:1), each maintained for 10 minutes. MP and respiratory parameters across the three I:E groups were compared using repeated-measures ANOVA. Results: Compared with the I:E ratio of 1:2, ventilation with an I:E ratio of 1:1 resulted in slower inspiratory gas flow, lower inspiratory resistance and peak inspiratory pressure, higher dynamic compliance, and lower MP values. Plateau pressure and driving pressure did not differ significantly. When comparing I:E 1:1 with I:E 1.5:1, a persistent slowing of inspiratory gas flow was observed, but no significant difference in MP was detected. Conclusion: In patients with ARDS, transitioning the I:E ratio from the conventional 1:2 to 1:1 or 1.5:1 resulted in progressively slower inspiratory gas flow and lower resistive and total mechanical power, suggesting that reducing inspiratory flow may enhance lung-protective ventilation.