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Expiratory Pause Maneuver to Assess Inspiratory Muscle Pressure During Assisted Mechanical Ventilation: A Bench Study

BACKGROUND: The generation of excessive inspiratory muscle pressure (Pmus) during assisted mechanical ventilation in patients with respiratory failure may result in acute respiratory muscle injury and/or fatigue, and exacerbate ventilator-induced lung injury. A readily available noninvasive surrogate measure of Pmus may help in titrating both mechanical ventilation and sedation to minimize these risks. This bench study explored the feasibility and accuracy of using a ventilator’s expiratory pause hold function to measure Pmus across multiple operators. METHODS: A standardized technique for executing a brief (<1 s) expiratory pause maneuver was used to measure the airway occlusion pressure change (Δ Paw) by using 3 simulated Pmus (Δ Pmus: 5, 10, 15 cm H2O) under (1) pressure support ventilation (0, 10, 15 cm H2O), (2) volume and pressure-regulated volume ventilation, (3) flow and pressure-triggering, and (4) varying levels of PEEP and pressure-rise time. Individual and grouped measurements were made by 4–7 clinicians on 3 different ventilators. The concordance between occlusion Δ Paw and Δ Pmus was arbitrarily set at ≤ 2 cm H2O. Data were evaluated by using analysis of variance and the Tukey-Kramer posttest. Correlation was assessed by using the Pearson R test; bias and precision were assessed by using the Bland-Altman method. Alpha was set at 0.05. RESULTS: Grouped expiratory pause maneuver measurements of occlusion Δ Paw across simulated Δ Pmus, mode and level of ventilatory support showed reasonable concordance, regardless of the ventilator used. Occlusion Δ Paw accuracy frequently decreased by ∼3 cm H2O when both pressure support ventilation and Δ Pmus reached 15 cm H2O. Expiratory pause maneuver accuracy was not affected by trigger mechanism and/or sensitivity, PEEP, or the post-trigger pressurization rate. In general, only small differences in Δ Paw occurred among the individual operators. CONCLUSIONS: The expiratory pause maneuver generally provided reproducible, stable approximations of Δ Pmus across ventilators and ventilator settings, and a range of simulated effort. Technique standardization produced relatively consistent results across multiple operators. The expiratory pause maneuver seemed feasible for general use in monitoring inspiratory effort during assisted mechanical ventilation.