Discussion
end-expiratory occlusion, ARDS, airway occlusion
ARDS
We have shown the feasibility and accuracy of using airway occlusion maneuvers to estimate respiratory effort in mechanically ventilated children with ARDS. Overall, we found Pocc, measured as the net negative deflection in airway pressure during inspiratory effort following an end-expiratory occlusion, showed the best correlation with esophageal pressure in all age groups and ventilation modes. PMI and P0.1 had reasonable correlations with esophageal pressure, but there was some variability as a function of age and mode of ventilation. Overall, the occlusion maneuvers that were conducted during expiratory holds (Pocc and P0.1) had a lower failure rate than PMI (inspiratory hold) and could be calculated on many more patients than PMI, which requires the patient to become passive during end-inspiration. We believe these findings support using Pocc more systematically to estimate respiratory effort amongst ventilated children, including potential use in clinical trials which require a measure of respiratory effort. We believe that using the equation ∆Pes = 0.66 × Pocc (Table There are multiple calculations which can be done with esophageal manometry to estimate patient effort, including work of breathing (which integrates esophageal pressure and spirometry and may incorporate respiratory rate), effort of breathing (pressure–time product, pressure rate product), and ∆Pes (peak to trough change in esophageal pressure) [These three airway occlusion parameters are related to one another but do represent different physiologic concepts. We found that Pocc had the strongest correlation with ∆Pes, which is expected. During airway occlusion, the total change in airway pressure should closely estimate the total change in esophageal pressure [P0.1 reflects the change in airway pressure during the first 100 ms of an inspiratory effort and is thought to reflect both respiratory effort and drive [PMI is calculated as the difference between plateau pressure and peak pressure during an end-inspiratory hold, and primarily reflects the elastic component of the respiratory system [There are several limitations to this study. First, it is primarily a physiologic study to evaluate the relationship between these parameters and ∆Pes. Hence, we do not know whether these parameters will be useful in clinical practice as we did not evaluate any relationship between these parameters and outcome, although that is a logical next step. Second, esophageal balloon calibration was conducted prior to measurements [