Effect of end-inspiratory pause duration on plateau pressure in mechanically ventilated patients

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Abstract
Objective. To compare the values of plateau pressure (Pplat) recorded at different times after end-inspiratory occlusion and those of static elastance (Est,rs) and total resistance (Rrs) of the respiratory system. Design. Physiological study. Setting. Medical intensive care unit of a university hospital. Patients. Eleven patients with ARDS and ten patients with COPD requiring tracheal intubation and mechanical ventilation were investigated. COPD patients were investigated on zero end-expiratory pressure (ZEEP) and ARDS patients on both ZEEP and positive end-expiratory pressure (PEEP). Measurements and results. Respiratory mechanics were assessed using the rapid airway occlusion technique. Tracheal pressure (Ptr) was measured downstream the endotracheal tube. Ptr was recorded 0.5 s, 1 s, 2 s, 3 s, and 5 s after a 5-s end-inspiratory occlusion. Est,rs and Rrs were computed at the same times using standard formula. In ARDS patients on ZEEP, Pplat amounted to 20±5, 20±5, 19±5, 19±5, and 18±5 cmH2O at 0.5, 1, 2, 3 and 5 s, respectively (P 2O, 17±4 cmH2O, 17±4 cmH2O, 16±4 cmH2O, and 16±4 cmH2O (P 2O, regardless of the time of measurement. As compared to 5 s, measurements at 0.5 s resulted in overestimation of Est,rs by 14% and 29% and in underestimation of Rrs by 34% and 24%, in ARDS and COPD patients, respectively. Conclusions. Very early post-occlusion values of Pplat were statistically greater than at 3 s or 5 s. This probably has no major impact on the occurrence of volutrauma. Clinicians must be aware, however, that Est,rs and Rrs are greatly modified by the time of recording of Pplat.