| Abstrakt: |
A 13-month-old, 10.5-kg infant with pediatric acute respiratory distress syndrome secondary to pneumonia underwent a positive end-expiratory pressure (PEEP) decrease monitored with electrical impedance tomography (Enlight 1800; Timpel). Under assistcontrol ventilation, PEEP was lowered from 13 cm H2O to 5 cm H2O, in steps of 2 cm H2O every 3 minutes, maintaining 10 cm H2O of driving pressure. From PEEP 9 cm H2O, electrical impedance tomography showed progressive lung collapse. At PEEP 5 cm H2O, respiratory instability was evident (Figure 1). Pendelluft, a phenomenon characterized by the movement of air between different lung regions, was recognized. Typically, dependent lung regions inflate first, causing deflation of nondependent areas at the start of inspiration. Toward the end of inspiration, the pressure gradient reverses as the diaphragm relaxes, causing the "extra air" to return to nondependent lung regions (Figure 2, PEEP 5). VT was kept at ~6-8 ml/kg. Restoring PEEP to 11 cm H2O did not resolve the pendelluft. Conversely, applying PEEP of 20 cm H2O for 5 minutes and later setting PEEP to 11 cm H2O minimized the pendelluft (Figure 2, recruitment maneuver1PEEP 11) (Video E1 in the online supplement). Pendelluft, described here for the first time in an infant, is a potentially harmful phenomenon that emerges in the context of lung injury and increased inspiratory efforts. The negative swings in pleural pressures concentrate close to the dependent lung zones, indicating that pleural pressures are not evenly transmitted through collapsed lungs (solid-like behavior). As a consequence, local overstretch, tidal recruitment, and inflammation can occur even when the set VT is protective (1--3). Higher PEEP decreases pendelluft owing to improved lung homogeneity (also homogenizing regional time constants), diminished respiratory drive, and flattening of the diaphragm (decreasing the efficiency of neuromechanical coupling) (2-4). Pendelluft detection can alert caregivers to the possibility of effort-dependent lung injury even with protective ventilatory settings by current standards (5). [ABSTRACT FROM AUTHOR] |
